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Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Browse Source 
Pull RCU changes for v3.4 from Ingo Molnar.  The major features of this
series are:

 - making RCU more aggressive about entering dyntick-idle mode in order
   to improve energy efficiency

 - converting a few more call_rcu()s to kfree_rcu()s

 - applying a number of rcutree fixes and cleanups to rcutiny

 - removing CONFIG_SMP #ifdefs from treercu

 - allowing RCU CPU stall times to be set via sysfs

 - adding CPU-stall capability to rcutorture

 - adding more RCU-abuse diagnostics

 - updating documentation

 - fixing yet more issues located by the still-ongoing top-to-bottom
   inspection of RCU, this time with a special focus on the CPU-hotplug
   code path.

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (48 commits)
  rcu: Stop spurious warnings from synchronize_sched_expedited
  rcu: Hold off RCU_FAST_NO_HZ after timer posted
  rcu: Eliminate softirq-mediated RCU_FAST_NO_HZ idle-entry loop
  rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections
  rcu: Allow nesting of rcu_idle_enter() and rcu_idle_exit()
  rcu: Remove redundant check for rcu_head misalignment
  PTR_ERR should be called before its argument is cleared.
  rcu: Convert WARN_ON_ONCE() in rcu_lock_acquire() to lockdep
  rcu: Trace only after NULL-pointer check
  rcu: Call out dangers of expedited RCU primitives
  rcu: Rework detection of use of RCU by offline CPUs
  lockdep: Add CPU-idle/offline warning to lockdep-RCU splat
  rcu: No interrupt disabling for rcu_prepare_for_idle()
  rcu: Move synchronize_sched_expedited() to rcutree.c
  rcu: Check for illegal use of RCU from offlined CPUs
  rcu: Update stall-warning documentation
  rcu: Add CPU-stall capability to rcutorture
  rcu: Make documentation give more realistic rcutorture duration
  rcutorture: Permit holding off CPU-hotplug operations during boot
  rcu: Print scheduling-clock information on RCU CPU stall-warning messages
  ...
This commit is contained in:
Linus Torvalds
2012-03-19 17:12:34 -07:00
parent 5ed59af850 bdd4431c8d
commit 5928a2b60c
29 changed files with 2909 additions and 586 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
kernel/lockdep.c
View File

@@ -4176,7 +4176,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
printk("-------------------------------\n");
printk("%s:%d %s!\n", file, line, s);
printk("\nother info that might help us debug this:\n\n");
printk("\nrcu_scheduler_active = %d, debug_locks = %d\n", rcu_scheduler_active, debug_locks);
printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
!rcu_lockdep_current_cpu_online()
? "RCU used illegally from offline CPU!\n"
: rcu_is_cpu_idle()
? "RCU used illegally from idle CPU!\n"
: "",
rcu_scheduler_active, debug_locks);
/*
* If a CPU is in the RCU-free window in idle (ie: in the section

26
kernel/rcu.h
View File

@@ -33,8 +33,27 @@
* Process-level increment to ->dynticks_nesting field. This allows for
* architectures that use half-interrupts and half-exceptions from
* process context.
*
* DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
* that counts the number of process-based reasons why RCU cannot
* consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
* is the value used to increment or decrement this field.
*
* The rest of the bits could in principle be used to count interrupts,
* but this would mean that a negative-one value in the interrupt
* field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
* We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
* that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
* The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
* initial exit from idle.
*/
#define DYNTICK_TASK_NESTING (LLONG_MAX / 2 - 1)
#define DYNTICK_TASK_NEST_WIDTH 7
#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
#define DYNTICK_TASK_NEST_MASK (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
#define DYNTICK_TASK_FLAG ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
#define DYNTICK_TASK_MASK ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
#define DYNTICK_TASK_EXIT_IDLE (DYNTICK_TASK_NEST_VALUE + \
DYNTICK_TASK_FLAG)
/*
* debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
@@ -50,7 +69,6 @@ extern struct debug_obj_descr rcuhead_debug_descr;
static inline void debug_rcu_head_queue(struct rcu_head *head)
{
WARN_ON_ONCE((unsigned long)head & 0x3);
debug_object_activate(head, &rcuhead_debug_descr);
debug_object_active_state(head, &rcuhead_debug_descr,
STATE_RCU_HEAD_READY,
@@ -76,16 +94,18 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
extern void kfree(const void *);
static inline void __rcu_reclaim(char *rn, struct rcu_head *head)
static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
{
unsigned long offset = (unsigned long)head->func;
if (__is_kfree_rcu_offset(offset)) {
RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
kfree((void *)head - offset);
return 1;
} else {
RCU_TRACE(trace_rcu_invoke_callback(rn, head));
head->func(head);
return 0;
}
}

5
kernel/rcupdate.c
View File

@@ -88,6 +88,9 @@ EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
* section.
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
*
* Note that rcu_read_lock() is disallowed if the CPU is either idle or
* offline from an RCU perspective, so check for those as well.
*/
int rcu_read_lock_bh_held(void)
{
@@ -95,6 +98,8 @@ int rcu_read_lock_bh_held(void)
return 1;
if (rcu_is_cpu_idle())
return 0;
if (!rcu_lockdep_current_cpu_online())
return 0;
return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);

26
kernel/rcutiny.c
View File

@@ -53,7 +53,7 @@ static void __call_rcu(struct rcu_head *head,
#include "rcutiny_plugin.h"
static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
static void rcu_idle_enter_common(long long oldval)
@@ -88,10 +88,16 @@ void rcu_idle_enter(void)
local_irq_save(flags);
oldval = rcu_dynticks_nesting;
rcu_dynticks_nesting = 0;
WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
DYNTICK_TASK_NEST_VALUE)
rcu_dynticks_nesting = 0;
else
rcu_dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
rcu_idle_enter_common(oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);
/*
* Exit an interrupt handler towards idle.
@@ -140,11 +146,15 @@ void rcu_idle_exit(void)
local_irq_save(flags);
oldval = rcu_dynticks_nesting;
WARN_ON_ONCE(oldval != 0);
rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
WARN_ON_ONCE(rcu_dynticks_nesting < 0);
if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
else
rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_idle_exit_common(oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);
/*
* Enter an interrupt handler, moving away from idle.
@@ -258,7 +268,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
/* If no RCU callbacks ready to invoke, just return. */
if (&rcp->rcucblist == rcp->donetail) {
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
ACCESS_ONCE(rcp->rcucblist),
need_resched(),
@@ -269,7 +279,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
/* Move the ready-to-invoke callbacks to a local list. */
local_irq_save(flags);
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
list = rcp->rcucblist;
rcp->rcucblist = *rcp->donetail;
*rcp->donetail = NULL;
@@ -319,6 +329,10 @@ static void rcu_process_callbacks(struct softirq_action *unused)
*/
void synchronize_sched(void)
{
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
!lock_is_held(&rcu_lock_map) &&
!lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_sched() in RCU read-side critical section");
cond_resched();
}
EXPORT_SYMBOL_GPL(synchronize_sched);

77
kernel/rcutiny_plugin.h
View File

@@ -132,6 +132,7 @@ static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
RCU_TRACE(.rcb.name = "rcu_preempt")
};
static void rcu_read_unlock_special(struct task_struct *t);
static int rcu_preempted_readers_exp(void);
static void rcu_report_exp_done(void);
@@ -146,6 +147,16 @@ static int rcu_cpu_blocking_cur_gp(void)
/*
* Check for a running RCU reader. Because there is only one CPU,
* there can be but one running RCU reader at a time. ;-)
*
* Returns zero if there are no running readers. Returns a positive
* number if there is at least one reader within its RCU read-side
* critical section. Returns a negative number if an outermost reader
* is in the midst of exiting from its RCU read-side critical section
*
* Returns zero if there are no running readers. Returns a positive
* number if there is at least one reader within its RCU read-side
* critical section. Returns a negative number if an outermost reader
* is in the midst of exiting from its RCU read-side critical section.
*/
static int rcu_preempt_running_reader(void)
{
@@ -307,7 +318,6 @@ static int rcu_boost(void)
t = container_of(tb, struct task_struct, rcu_node_entry);
rt_mutex_init_proxy_locked(&mtx, t);
t->rcu_boost_mutex = &mtx;
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
raw_local_irq_restore(flags);
rt_mutex_lock(&mtx);
rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
@@ -475,7 +485,7 @@ void rcu_preempt_note_context_switch(void)
unsigned long flags;
local_irq_save(flags); /* must exclude scheduler_tick(). */
if (rcu_preempt_running_reader() &&
if (rcu_preempt_running_reader() > 0 &&
(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
/* Possibly blocking in an RCU read-side critical section. */
@@ -494,6 +504,13 @@ void rcu_preempt_note_context_switch(void)
list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
if (rcu_cpu_blocking_cur_gp())
rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
} else if (rcu_preempt_running_reader() < 0 &&
t->rcu_read_unlock_special) {
/*
* Complete exit from RCU read-side critical section on
* behalf of preempted instance of __rcu_read_unlock().
*/
rcu_read_unlock_special(t);
}
/*
@@ -526,12 +543,15 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock);
* notify RCU core processing or task having blocked during the RCU
* read-side critical section.
*/
static void rcu_read_unlock_special(struct task_struct *t)
static noinline void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
int empty_exp;
unsigned long flags;
struct list_head *np;
#ifdef CONFIG_RCU_BOOST
struct rt_mutex *rbmp = NULL;
#endif /* #ifdef CONFIG_RCU_BOOST */
int special;
/*
@@ -552,7 +572,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
rcu_preempt_cpu_qs();
/* Hardware IRQ handlers cannot block. */
if (in_irq()) {
if (in_irq() || in_serving_softirq()) {
local_irq_restore(flags);
return;
}
@@ -597,10 +617,10 @@ static void rcu_read_unlock_special(struct task_struct *t)
}
#ifdef CONFIG_RCU_BOOST
/* Unboost self if was boosted. */
if (special & RCU_READ_UNLOCK_BOOSTED) {
t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
rt_mutex_unlock(t->rcu_boost_mutex);
if (t->rcu_boost_mutex != NULL) {
rbmp = t->rcu_boost_mutex;
t->rcu_boost_mutex = NULL;
rt_mutex_unlock(rbmp);
}
#endif /* #ifdef CONFIG_RCU_BOOST */
local_irq_restore(flags);
@@ -618,13 +638,22 @@ void __rcu_read_unlock(void)
struct task_struct *t = current;
barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */
--t->rcu_read_lock_nesting;
barrier(); /* decrement before load of ->rcu_read_unlock_special */
if (t->rcu_read_lock_nesting == 0 &&
unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
rcu_read_unlock_special(t);
if (t->rcu_read_lock_nesting != 1)
--t->rcu_read_lock_nesting;
else {
t->rcu_read_lock_nesting = INT_MIN;
barrier(); /* assign before ->rcu_read_unlock_special load */
if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
rcu_read_unlock_special(t);
barrier(); /* ->rcu_read_unlock_special load before assign */
t->rcu_read_lock_nesting = 0;
}
#ifdef CONFIG_PROVE_LOCKING
WARN_ON_ONCE(t->rcu_read_lock_nesting < 0);
{
int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
}
#endif /* #ifdef CONFIG_PROVE_LOCKING */
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
@@ -649,7 +678,7 @@ static void rcu_preempt_check_callbacks(void)
invoke_rcu_callbacks();
if (rcu_preempt_gp_in_progress() &&
rcu_cpu_blocking_cur_gp() &&
rcu_preempt_running_reader())
rcu_preempt_running_reader() > 0)
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
}
@@ -706,6 +735,11 @@ EXPORT_SYMBOL_GPL(call_rcu);
*/
void synchronize_rcu(void)
{
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
!lock_is_held(&rcu_lock_map) &&
!lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
#ifdef CONFIG_DEBUG_LOCK_ALLOC
if (!rcu_scheduler_active)
return;
@@ -882,7 +916,8 @@ static void rcu_preempt_process_callbacks(void)
static void invoke_rcu_callbacks(void)
{
have_rcu_kthread_work = 1;
wake_up(&rcu_kthread_wq);
if (rcu_kthread_task != NULL)
wake_up(&rcu_kthread_wq);
}
#ifdef CONFIG_RCU_TRACE
@@ -943,12 +978,16 @@ early_initcall(rcu_spawn_kthreads);
#else /* #ifdef CONFIG_RCU_BOOST */
/* Hold off callback invocation until early_initcall() time. */
static int rcu_scheduler_fully_active __read_mostly;
/*
* Start up softirq processing of callbacks.
*/
void invoke_rcu_callbacks(void)
{
raise_softirq(RCU_SOFTIRQ);
if (rcu_scheduler_fully_active)
raise_softirq(RCU_SOFTIRQ);
}
#ifdef CONFIG_RCU_TRACE
@@ -963,10 +1002,14 @@ static bool rcu_is_callbacks_kthread(void)
#endif /* #ifdef CONFIG_RCU_TRACE */
void rcu_init(void)
static int __init rcu_scheduler_really_started(void)
{
rcu_scheduler_fully_active = 1;
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
raise_softirq(RCU_SOFTIRQ); /* Invoke any callbacks from early boot. */
return 0;
}
early_initcall(rcu_scheduler_really_started);
#endif /* #else #ifdef CONFIG_RCU_BOOST */

91
kernel/rcutorture.c
View File

@@ -65,7 +65,10 @@ static int fqs_duration; /* Duration of bursts (us), 0 to disable. */
static int fqs_holdoff; /* Hold time within burst (us). */
static int fqs_stutter = 3; /* Wait time between bursts (s). */
static int onoff_interval; /* Wait time between CPU hotplugs, 0=disable. */
static int onoff_holdoff; /* Seconds after boot before CPU hotplugs. */
static int shutdown_secs; /* Shutdown time (s). <=0 for no shutdown. */
static int stall_cpu; /* CPU-stall duration (s). 0 for no stall. */
static int stall_cpu_holdoff = 10; /* Time to wait until stall (s). */
static int test_boost = 1; /* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */
static int test_boost_interval = 7; /* Interval between boost tests, seconds. */
static int test_boost_duration = 4; /* Duration of each boost test, seconds. */
@@ -95,8 +98,14 @@ module_param(fqs_stutter, int, 0444);
MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
module_param(onoff_interval, int, 0444);
MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable");
module_param(onoff_holdoff, int, 0444);
MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)");
module_param(shutdown_secs, int, 0444);
MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), zero to disable.");
module_param(stall_cpu, int, 0444);
MODULE_PARM_DESC(stall_cpu, "Stall duration (s), zero to disable.");
module_param(stall_cpu_holdoff, int, 0444);
MODULE_PARM_DESC(stall_cpu_holdoff, "Time to wait before starting stall (s).");
module_param(test_boost, int, 0444);
MODULE_PARM_DESC(test_boost, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
module_param(test_boost_interval, int, 0444);
@@ -129,6 +138,7 @@ static struct task_struct *shutdown_task;
#ifdef CONFIG_HOTPLUG_CPU
static struct task_struct *onoff_task;
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static struct task_struct *stall_task;
#define RCU_TORTURE_PIPE_LEN 10
@@ -990,12 +1000,12 @@ static void rcu_torture_timer(unsigned long unused)
rcu_read_lock_bh_held() ||
rcu_read_lock_sched_held() ||
srcu_read_lock_held(&srcu_ctl));
do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
if (p == NULL) {
/* Leave because rcu_torture_writer is not yet underway */
cur_ops->readunlock(idx);
return;
}
do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
if (p->rtort_mbtest == 0)
atomic_inc(&n_rcu_torture_mberror);
spin_lock(&rand_lock);
@@ -1053,13 +1063,13 @@ rcu_torture_reader(void *arg)
rcu_read_lock_bh_held() ||
rcu_read_lock_sched_held() ||
srcu_read_lock_held(&srcu_ctl));
do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
if (p == NULL) {
/* Wait for rcu_torture_writer to get underway */
cur_ops->readunlock(idx);
schedule_timeout_interruptible(HZ);
continue;
}
do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
if (p->rtort_mbtest == 0)
atomic_inc(&n_rcu_torture_mberror);
cur_ops->read_delay(&rand);
@@ -1300,13 +1310,13 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag)
"fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d "
"test_boost=%d/%d test_boost_interval=%d "
"test_boost_duration=%d shutdown_secs=%d "
"onoff_interval=%d\n",
"onoff_interval=%d onoff_holdoff=%d\n",
torture_type, tag, nrealreaders, nfakewriters,
stat_interval, verbose, test_no_idle_hz, shuffle_interval,
stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
test_boost, cur_ops->can_boost,
test_boost_interval, test_boost_duration, shutdown_secs,
onoff_interval);
onoff_interval, onoff_holdoff);
}
static struct notifier_block rcutorture_shutdown_nb = {
@@ -1410,6 +1420,11 @@ rcu_torture_onoff(void *arg)
for_each_online_cpu(cpu)
maxcpu = cpu;
WARN_ON(maxcpu < 0);
if (onoff_holdoff > 0) {
VERBOSE_PRINTK_STRING("rcu_torture_onoff begin holdoff");
schedule_timeout_interruptible(onoff_holdoff * HZ);
VERBOSE_PRINTK_STRING("rcu_torture_onoff end holdoff");
}
while (!kthread_should_stop()) {
cpu = (rcu_random(&rand) >> 4) % (maxcpu + 1);
if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) {
@@ -1450,12 +1465,15 @@ rcu_torture_onoff(void *arg)
static int __cpuinit
rcu_torture_onoff_init(void)
{
int ret;
if (onoff_interval <= 0)
return 0;
onoff_task = kthread_run(rcu_torture_onoff, NULL, "rcu_torture_onoff");
if (IS_ERR(onoff_task)) {
ret = PTR_ERR(onoff_task);
onoff_task = NULL;
return PTR_ERR(onoff_task);
return ret;
}
return 0;
}
@@ -1481,6 +1499,63 @@ static void rcu_torture_onoff_cleanup(void)
#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
/*
* CPU-stall kthread. It waits as specified by stall_cpu_holdoff, then
* induces a CPU stall for the time specified by stall_cpu.
*/
static int __cpuinit rcu_torture_stall(void *args)
{
unsigned long stop_at;
VERBOSE_PRINTK_STRING("rcu_torture_stall task started");
if (stall_cpu_holdoff > 0) {
VERBOSE_PRINTK_STRING("rcu_torture_stall begin holdoff");
schedule_timeout_interruptible(stall_cpu_holdoff * HZ);
VERBOSE_PRINTK_STRING("rcu_torture_stall end holdoff");
}
if (!kthread_should_stop()) {
stop_at = get_seconds() + stall_cpu;
/* RCU CPU stall is expected behavior in following code. */
printk(KERN_ALERT "rcu_torture_stall start.\n");
rcu_read_lock();
preempt_disable();
while (ULONG_CMP_LT(get_seconds(), stop_at))
continue; /* Induce RCU CPU stall warning. */
preempt_enable();
rcu_read_unlock();
printk(KERN_ALERT "rcu_torture_stall end.\n");
}
rcutorture_shutdown_absorb("rcu_torture_stall");
while (!kthread_should_stop())
schedule_timeout_interruptible(10 * HZ);
return 0;
}
/* Spawn CPU-stall kthread, if stall_cpu specified. */
static int __init rcu_torture_stall_init(void)
{
int ret;
if (stall_cpu <= 0)
return 0;
stall_task = kthread_run(rcu_torture_stall, NULL, "rcu_torture_stall");
if (IS_ERR(stall_task)) {
ret = PTR_ERR(stall_task);
stall_task = NULL;
return ret;
}
return 0;
}
/* Clean up after the CPU-stall kthread, if one was spawned. */
static void rcu_torture_stall_cleanup(void)
{
if (stall_task == NULL)
return;
VERBOSE_PRINTK_STRING("Stopping rcu_torture_stall_task.");
kthread_stop(stall_task);
}
static int rcutorture_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
@@ -1523,6 +1598,7 @@ rcu_torture_cleanup(void)
fullstop = FULLSTOP_RMMOD;
mutex_unlock(&fullstop_mutex);
unregister_reboot_notifier(&rcutorture_shutdown_nb);
rcu_torture_stall_cleanup();
if (stutter_task) {
VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task");
kthread_stop(stutter_task);
@@ -1602,6 +1678,10 @@ rcu_torture_cleanup(void)
cur_ops->cleanup();
if (atomic_read(&n_rcu_torture_error))
rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE");
else if (n_online_successes != n_online_attempts ||
n_offline_successes != n_offline_attempts)
rcu_torture_print_module_parms(cur_ops,
"End of test: RCU_HOTPLUG");
else
rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
}
@@ -1819,6 +1899,7 @@ rcu_torture_init(void)
}
rcu_torture_onoff_init();
register_reboot_notifier(&rcutorture_shutdown_nb);
rcu_torture_stall_init();
rcutorture_record_test_transition();
mutex_unlock(&fullstop_mutex);
return 0;

507
kernel/rcutree.c
View File

@@ -50,6 +50,8 @@
#include <linux/wait.h>
#include <linux/kthread.h>
#include <linux/prefetch.h>
#include <linux/delay.h>
#include <linux/stop_machine.h>
#include "rcutree.h"
#include <trace/events/rcu.h>
@@ -196,7 +198,7 @@ void rcu_note_context_switch(int cpu)
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
.dynticks_nesting = DYNTICK_TASK_NESTING,
.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
.dynticks = ATOMIC_INIT(1),
};
@@ -208,8 +210,11 @@ module_param(blimit, int, 0);
module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);
int rcu_cpu_stall_suppress __read_mostly;
int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
module_param(rcu_cpu_stall_suppress, int, 0644);
module_param(rcu_cpu_stall_timeout, int, 0644);
static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
static int rcu_pending(int cpu);
@@ -301,8 +306,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
return &rsp->node[0];
}
#ifdef CONFIG_SMP
/*
* If the specified CPU is offline, tell the caller that it is in
* a quiescent state. Otherwise, whack it with a reschedule IPI.
@@ -317,30 +320,21 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
static int rcu_implicit_offline_qs(struct rcu_data *rdp)
{
/*
* If the CPU is offline, it is in a quiescent state. We can
* trust its state not to change because interrupts are disabled.
* If the CPU is offline for more than a jiffy, it is in a quiescent
* state. We can trust its state not to change because interrupts
* are disabled. The reason for the jiffy's worth of slack is to
* handle CPUs initializing on the way up and finding their way
* to the idle loop on the way down.
*/
if (cpu_is_offline(rdp->cpu)) {
if (cpu_is_offline(rdp->cpu) &&
ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
rdp->offline_fqs++;
return 1;
}
/*
* The CPU is online, so send it a reschedule IPI. This forces
* it through the scheduler, and (inefficiently) also handles cases
* where idle loops fail to inform RCU about the CPU being idle.
*/
if (rdp->cpu != smp_processor_id())
smp_send_reschedule(rdp->cpu);
else
set_need_resched();
rdp->resched_ipi++;
return 0;
}
#endif /* #ifdef CONFIG_SMP */
/*
* rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
*
@@ -366,6 +360,17 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
atomic_inc(&rdtp->dynticks);
smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
/*
* The idle task is not permitted to enter the idle loop while
* in an RCU read-side critical section.
*/
rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
"Illegal idle entry in RCU read-side critical section.");
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
"Illegal idle entry in RCU-bh read-side critical section.");
rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
"Illegal idle entry in RCU-sched read-side critical section.");
}
/**
@@ -389,10 +394,15 @@ void rcu_idle_enter(void)
local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting = 0;
WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
rdtp->dynticks_nesting = 0;
else
rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
rcu_idle_enter_common(rdtp, oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);
/**
* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
@@ -462,7 +472,7 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
* Exit idle mode, in other words, -enter- the mode in which RCU
* read-side critical sections can occur.
*
* We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to
* We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
* allow for the possibility of usermode upcalls messing up our count
* of interrupt nesting level during the busy period that is just
* now starting.
@@ -476,11 +486,15 @@ void rcu_idle_exit(void)
local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
oldval = rdtp->dynticks_nesting;
WARN_ON_ONCE(oldval != 0);
rdtp->dynticks_nesting = DYNTICK_TASK_NESTING;
WARN_ON_ONCE(oldval < 0);
if (oldval & DYNTICK_TASK_NEST_MASK)
rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
else
rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_idle_exit_common(rdtp, oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);
/**
* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
@@ -581,6 +595,49 @@ int rcu_is_cpu_idle(void)
}
EXPORT_SYMBOL(rcu_is_cpu_idle);
#ifdef CONFIG_HOTPLUG_CPU
/*
* Is the current CPU online? Disable preemption to avoid false positives
* that could otherwise happen due to the current CPU number being sampled,
* this task being preempted, its old CPU being taken offline, resuming
* on some other CPU, then determining that its old CPU is now offline.
* It is OK to use RCU on an offline processor during initial boot, hence
* the check for rcu_scheduler_fully_active. Note also that it is OK
* for a CPU coming online to use RCU for one jiffy prior to marking itself
* online in the cpu_online_mask. Similarly, it is OK for a CPU going
* offline to continue to use RCU for one jiffy after marking itself
* offline in the cpu_online_mask. This leniency is necessary given the
* non-atomic nature of the online and offline processing, for example,
* the fact that a CPU enters the scheduler after completing the CPU_DYING
* notifiers.
*
* This is also why RCU internally marks CPUs online during the
* CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
*
* Disable checking if in an NMI handler because we cannot safely report
* errors from NMI handlers anyway.
*/
bool rcu_lockdep_current_cpu_online(void)
{
struct rcu_data *rdp;
struct rcu_node *rnp;
bool ret;
if (in_nmi())
return 1;
preempt_disable();
rdp = &__get_cpu_var(rcu_sched_data);
rnp = rdp->mynode;
ret = (rdp->grpmask & rnp->qsmaskinit) ||
!rcu_scheduler_fully_active;
preempt_enable();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
#endif /* #ifdef CONFIG_PROVE_RCU */
/**
@@ -595,8 +652,6 @@ int rcu_is_cpu_rrupt_from_idle(void)
return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1;
}
#ifdef CONFIG_SMP
/*
* Snapshot the specified CPU's dynticks counter so that we can later
* credit them with an implicit quiescent state. Return 1 if this CPU
@@ -640,12 +695,28 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
return rcu_implicit_offline_qs(rdp);
}
#endif /* #ifdef CONFIG_SMP */
static int jiffies_till_stall_check(void)
{
int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
/*
* Limit check must be consistent with the Kconfig limits
* for CONFIG_RCU_CPU_STALL_TIMEOUT.
*/
if (till_stall_check < 3) {
ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
till_stall_check = 3;
} else if (till_stall_check > 300) {
ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
till_stall_check = 300;
}
return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
}
static void record_gp_stall_check_time(struct rcu_state *rsp)
{
rsp->gp_start = jiffies;
rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
rsp->jiffies_stall = jiffies + jiffies_till_stall_check();
}
static void print_other_cpu_stall(struct rcu_state *rsp)
@@ -664,13 +735,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
/*
* Now rat on any tasks that got kicked up to the root rcu_node
* due to CPU offlining.
*/
ndetected = rcu_print_task_stall(rnp);
rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
/*
@@ -678,8 +743,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {",
printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:",
rsp->name);
print_cpu_stall_info_begin();
rcu_for_each_leaf_node(rsp, rnp) {
raw_spin_lock_irqsave(&rnp->lock, flags);
ndetected += rcu_print_task_stall(rnp);
@@ -688,11 +754,22 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
continue;
for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
if (rnp->qsmask & (1UL << cpu)) {
printk(" %d", rnp->grplo + cpu);
print_cpu_stall_info(rsp, rnp->grplo + cpu);
ndetected++;
}
}
printk("} (detected by %d, t=%ld jiffies)\n",
/*
* Now rat on any tasks that got kicked up to the root rcu_node
* due to CPU offlining.
*/
rnp = rcu_get_root(rsp);
raw_spin_lock_irqsave(&rnp->lock, flags);
ndetected = rcu_print_task_stall(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
print_cpu_stall_info_end();
printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n",
smp_processor_id(), (long)(jiffies - rsp->gp_start));
if (ndetected == 0)
printk(KERN_ERR "INFO: Stall ended before state dump start\n");
@@ -716,15 +793,18 @@ static void print_cpu_stall(struct rcu_state *rsp)
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
rsp->name, smp_processor_id(), jiffies - rsp->gp_start);
printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name);
print_cpu_stall_info_begin();
print_cpu_stall_info(rsp, smp_processor_id());
print_cpu_stall_info_end();
printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start);
if (!trigger_all_cpu_backtrace())
dump_stack();
raw_spin_lock_irqsave(&rnp->lock, flags);
if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
rsp->jiffies_stall =
jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
rsp->jiffies_stall = jiffies +
3 * jiffies_till_stall_check() + 3;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
set_need_resched(); /* kick ourselves to get things going. */
@@ -807,6 +887,7 @@ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct
rdp->passed_quiesce = 0;
} else
rdp->qs_pending = 0;
zero_cpu_stall_ticks(rdp);
}
}
@@ -943,6 +1024,10 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
* in preparation for detecting the next grace period. The caller must hold
* the root node's ->lock, which is released before return. Hard irqs must
* be disabled.
*
* Note that it is legal for a dying CPU (which is marked as offline) to
* invoke this function. This can happen when the dying CPU reports its
* quiescent state.
*/
static void
rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
@@ -980,26 +1065,8 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
rsp->fqs_state = RCU_GP_INIT; /* Hold off force_quiescent_state. */
rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
record_gp_stall_check_time(rsp);
/* Special-case the common single-level case. */
if (NUM_RCU_NODES == 1) {
rcu_preempt_check_blocked_tasks(rnp);
rnp->qsmask = rnp->qsmaskinit;
rnp->gpnum = rsp->gpnum;
rnp->completed = rsp->completed;
rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state OK */
rcu_start_gp_per_cpu(rsp, rnp, rdp);
rcu_preempt_boost_start_gp(rnp);
trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
rnp->level, rnp->grplo,
rnp->grphi, rnp->qsmask);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */
/* Exclude any concurrent CPU-hotplug operations. */
raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
@@ -1245,53 +1312,115 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
/*
* Move a dying CPU's RCU callbacks to online CPU's callback list.
* Synchronization is not required because this function executes
* in stop_machine() context.
* Also record a quiescent state for this CPU for the current grace period.
* Synchronization and interrupt disabling are not required because
* this function executes in stop_machine() context. Therefore, cleanup
* operations that might block must be done later from the CPU_DEAD
* notifier.
*
* Note that the outgoing CPU's bit has already been cleared in the
* cpu_online_mask. This allows us to randomly pick a callback
* destination from the bits set in that mask.
*/
static void rcu_send_cbs_to_online(struct rcu_state *rsp)
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
int i;
/* current DYING CPU is cleared in the cpu_online_mask */
unsigned long mask;
int receive_cpu = cpumask_any(cpu_online_mask);
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
RCU_TRACE(struct rcu_node *rnp = rdp->mynode); /* For dying CPU. */
if (rdp->nxtlist == NULL)
return; /* irqs disabled, so comparison is stable. */
/* First, adjust the counts. */
if (rdp->nxtlist != NULL) {
receive_rdp->qlen_lazy += rdp->qlen_lazy;
receive_rdp->qlen += rdp->qlen;
rdp->qlen_lazy = 0;
rdp->qlen = 0;
}
*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
receive_rdp->qlen += rdp->qlen;
receive_rdp->n_cbs_adopted += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
/*
* Next, move ready-to-invoke callbacks to be invoked on some
* other CPU. These will not be required to pass through another
* grace period: They are done, regardless of CPU.
*/
if (rdp->nxtlist != NULL &&
rdp->nxttail[RCU_DONE_TAIL] != &rdp->nxtlist) {
struct rcu_head *oldhead;
struct rcu_head **oldtail;
struct rcu_head **newtail;
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
rdp->qlen = 0;
oldhead = rdp->nxtlist;
oldtail = receive_rdp->nxttail[RCU_DONE_TAIL];
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = *oldtail;
*receive_rdp->nxttail[RCU_DONE_TAIL] = oldhead;
newtail = rdp->nxttail[RCU_DONE_TAIL];
for (i = RCU_DONE_TAIL; i < RCU_NEXT_SIZE; i++) {
if (receive_rdp->nxttail[i] == oldtail)
receive_rdp->nxttail[i] = newtail;
if (rdp->nxttail[i] == newtail)
rdp->nxttail[i] = &rdp->nxtlist;
}
}
/*
* Finally, put the rest of the callbacks at the end of the list.
* The ones that made it partway through get to start over: We
* cannot assume that grace periods are synchronized across CPUs.
* (We could splice RCU_WAIT_TAIL into RCU_NEXT_READY_TAIL, but
* this does not seem compelling. Not yet, anyway.)
*/
if (rdp->nxtlist != NULL) {
*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
receive_rdp->nxttail[RCU_NEXT_TAIL] =
rdp->nxttail[RCU_NEXT_TAIL];
receive_rdp->n_cbs_adopted += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
}
/*
* Record a quiescent state for the dying CPU. This is safe
* only because we have already cleared out the callbacks.
* (Otherwise, the RCU core might try to schedule the invocation
* of callbacks on this now-offline CPU, which would be bad.)
*/
mask = rdp->grpmask; /* rnp->grplo is constant. */
trace_rcu_grace_period(rsp->name,
rnp->gpnum + 1 - !!(rnp->qsmask & mask),
"cpuofl");
rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum);
/* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
}
/*
* Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
* and move all callbacks from the outgoing CPU to the current one.
* The CPU has been completely removed, and some other CPU is reporting
* this fact from process context. Do the remainder of the cleanup.
* There can only be one CPU hotplug operation at a time, so no other
* CPU can be attempting to update rcu_cpu_kthread_task.
*/
static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
unsigned long mask;
int need_report = 0;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp;
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rnp. */
/* Adjust any no-longer-needed kthreads. */
rcu_stop_cpu_kthread(cpu);
rcu_node_kthread_setaffinity(rnp, -1);
/* Remove the dying CPU from the bitmasks in the rcu_node hierarchy. */
/* Exclude any attempts to start a new grace period. */
raw_spin_lock_irqsave(&rsp->onofflock, flags);
/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
mask = rdp->grpmask; /* rnp->grplo is constant. */
do {
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
@@ -1299,20 +1428,11 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
if (rnp->qsmaskinit != 0) {
if (rnp != rdp->mynode)
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
else
trace_rcu_grace_period(rsp->name,
rnp->gpnum + 1 -
!!(rnp->qsmask & mask),
"cpuofl");
break;
}
if (rnp == rdp->mynode) {
trace_rcu_grace_period(rsp->name,
rnp->gpnum + 1 -
!!(rnp->qsmask & mask),
"cpuofl");
if (rnp == rdp->mynode)
need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
} else
else
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
mask = rnp->grpmask;
rnp = rnp->parent;
@@ -1332,29 +1452,15 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp, true);
rcu_node_kthread_setaffinity(rnp, -1);
}
/*
* Remove the specified CPU from the RCU hierarchy and move any pending
* callbacks that it might have to the current CPU. This code assumes
* that at least one CPU in the system will remain running at all times.
* Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
*/
static void rcu_offline_cpu(int cpu)
{
__rcu_offline_cpu(cpu, &rcu_sched_state);
__rcu_offline_cpu(cpu, &rcu_bh_state);
rcu_preempt_offline_cpu(cpu);
}
#else /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_send_cbs_to_online(struct rcu_state *rsp)
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
}
static void rcu_offline_cpu(int cpu)
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
}
@@ -1368,11 +1474,11 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_head *next, *list, **tail;
int bl, count;
int bl, count, count_lazy;
/* If no callbacks are ready, just return.*/
if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
trace_rcu_batch_start(rsp->name, 0, 0);
trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
@@ -1384,8 +1490,9 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
* races with call_rcu() from interrupt handlers.
*/
local_irq_save(flags);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
bl = rdp->blimit;
trace_rcu_batch_start(rsp->name, rdp->qlen, bl);
trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
list = rdp->nxtlist;
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = NULL;
@@ -1396,12 +1503,13 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
local_irq_restore(flags);
/* Invoke callbacks. */
count = 0;
count = count_lazy = 0;
while (list) {
next = list->next;
prefetch(next);
debug_rcu_head_unqueue(list);
__rcu_reclaim(rsp->name, list);
if (__rcu_reclaim(rsp->name, list))
count_lazy++;
list = next;
/* Stop only if limit reached and CPU has something to do. */
if (++count >= bl &&
@@ -1416,6 +1524,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
rcu_is_callbacks_kthread());
/* Update count, and requeue any remaining callbacks. */
rdp->qlen_lazy -= count_lazy;
rdp->qlen -= count;
rdp->n_cbs_invoked += count;
if (list != NULL) {
@@ -1458,6 +1567,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
void rcu_check_callbacks(int cpu, int user)
{
trace_rcu_utilization("Start scheduler-tick");
increment_cpu_stall_ticks();
if (user || rcu_is_cpu_rrupt_from_idle()) {
/*
@@ -1492,8 +1602,6 @@ void rcu_check_callbacks(int cpu, int user)
trace_rcu_utilization("End scheduler-tick");
}
#ifdef CONFIG_SMP
/*
* Scan the leaf rcu_node structures, processing dyntick state for any that
* have not yet encountered a quiescent state, using the function specified.
@@ -1616,15 +1724,6 @@ unlock_fqs_ret:
trace_rcu_utilization("End fqs");
}
#else /* #ifdef CONFIG_SMP */
static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
{
set_need_resched();
}
#endif /* #else #ifdef CONFIG_SMP */
/*
* This does the RCU core processing work for the specified rcu_state
* and rcu_data structures. This may be called only from the CPU to
@@ -1702,11 +1801,12 @@ static void invoke_rcu_core(void)
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_state *rsp)
struct rcu_state *rsp, bool lazy)
{
unsigned long flags;
struct rcu_data *rdp;
WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
debug_rcu_head_queue(head);
head->func = func;
head->next = NULL;
@@ -1720,18 +1820,21 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
* a quiescent state betweentimes.
*/
local_irq_save(flags);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
rdp = this_cpu_ptr(rsp->rda);
/* Add the callback to our list. */
*rdp->nxttail[RCU_NEXT_TAIL] = head;
rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
rdp->qlen++;
if (lazy)
rdp->qlen_lazy++;
if (__is_kfree_rcu_offset((unsigned long)func))
trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
rdp->qlen);
rdp->qlen_lazy, rdp->qlen);
else
trace_rcu_callback(rsp->name, head, rdp->qlen);
trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
/* If interrupts were disabled, don't dive into RCU core. */
if (irqs_disabled_flags(flags)) {
@@ -1778,16 +1881,16 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
*/
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_sched_state);
__call_rcu(head, func, &rcu_sched_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);
/*
* Queue an RCU for invocation after a quicker grace period.
* Queue an RCU callback for invocation after a quicker grace period.
*/
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_bh_state);
__call_rcu(head, func, &rcu_bh_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
@@ -1816,6 +1919,10 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
*/
void synchronize_sched(void)
{
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
!lock_is_held(&rcu_lock_map) &&
!lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_sched() in RCU-sched read-side critical section");
if (rcu_blocking_is_gp())
return;
wait_rcu_gp(call_rcu_sched);
@@ -1833,12 +1940,137 @@ EXPORT_SYMBOL_GPL(synchronize_sched);
*/
void synchronize_rcu_bh(void)
{
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
!lock_is_held(&rcu_lock_map) &&
!lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
if (rcu_blocking_is_gp())
return;
wait_rcu_gp(call_rcu_bh);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
static int synchronize_sched_expedited_cpu_stop(void *data)
{
/*
* There must be a full memory barrier on each affected CPU
* between the time that try_stop_cpus() is called and the
* time that it returns.
*
* In the current initial implementation of cpu_stop, the
* above condition is already met when the control reaches
* this point and the following smp_mb() is not strictly
* necessary. Do smp_mb() anyway for documentation and
* robustness against future implementation changes.
*/
smp_mb(); /* See above comment block. */
return 0;
}
/**
* synchronize_sched_expedited - Brute-force RCU-sched grace period
*
* Wait for an RCU-sched grace period to elapse, but use a "big hammer"
* approach to force the grace period to end quickly. This consumes
* significant time on all CPUs and is unfriendly to real-time workloads,
* so is thus not recommended for any sort of common-case code. In fact,
* if you are using synchronize_sched_expedited() in a loop, please
* restructure your code to batch your updates, and then use a single
* synchronize_sched() instead.
*
* Note that it is illegal to call this function while holding any lock
* that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
* to call this function from a CPU-hotplug notifier. Failing to observe
* these restriction will result in deadlock.
*
* This implementation can be thought of as an application of ticket
* locking to RCU, with sync_sched_expedited_started and
* sync_sched_expedited_done taking on the roles of the halves
* of the ticket-lock word. Each task atomically increments
* sync_sched_expedited_started upon entry, snapshotting the old value,
* then attempts to stop all the CPUs. If this succeeds, then each
* CPU will have executed a context switch, resulting in an RCU-sched
* grace period. We are then done, so we use atomic_cmpxchg() to
* update sync_sched_expedited_done to match our snapshot -- but
* only if someone else has not already advanced past our snapshot.
*
* On the other hand, if try_stop_cpus() fails, we check the value
* of sync_sched_expedited_done. If it has advanced past our
* initial snapshot, then someone else must have forced a grace period
* some time after we took our snapshot. In this case, our work is
* done for us, and we can simply return. Otherwise, we try again,
* but keep our initial snapshot for purposes of checking for someone
* doing our work for us.
*
* If we fail too many times in a row, we fall back to synchronize_sched().
*/
void synchronize_sched_expedited(void)
{
int firstsnap, s, snap, trycount = 0;
/* Note that atomic_inc_return() implies full memory barrier. */
firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
get_online_cpus();
WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
/*
* Each pass through the following loop attempts to force a
* context switch on each CPU.
*/
while (try_stop_cpus(cpu_online_mask,
synchronize_sched_expedited_cpu_stop,
NULL) == -EAGAIN) {
put_online_cpus();
/* No joy, try again later. Or just synchronize_sched(). */
if (trycount++ < 10)
udelay(trycount * num_online_cpus());
else {
synchronize_sched();
return;
}
/* Check to see if someone else did our work for us. */
s = atomic_read(&sync_sched_expedited_done);
if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
smp_mb(); /* ensure test happens before caller kfree */
return;
}
/*
* Refetching sync_sched_expedited_started allows later
* callers to piggyback on our grace period. We subtract
* 1 to get the same token that the last incrementer got.
* We retry after they started, so our grace period works
* for them, and they started after our first try, so their
* grace period works for us.
*/
get_online_cpus();
snap = atomic_read(&sync_sched_expedited_started);
smp_mb(); /* ensure read is before try_stop_cpus(). */
}
/*
* Everyone up to our most recent fetch is covered by our grace
* period. Update the counter, but only if our work is still
* relevant -- which it won't be if someone who started later
* than we did beat us to the punch.
*/
do {
s = atomic_read(&sync_sched_expedited_done);
if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
smp_mb(); /* ensure test happens before caller kfree */
break;
}
} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
/*
* Check to see if there is any immediate RCU-related work to be done
* by the current CPU, for the specified type of RCU, returning 1 if so.
@@ -1932,7 +2164,7 @@ static int rcu_cpu_has_callbacks(int cpu)
/* RCU callbacks either ready or pending? */
return per_cpu(rcu_sched_data, cpu).nxtlist ||
per_cpu(rcu_bh_data, cpu).nxtlist ||
rcu_preempt_needs_cpu(cpu);
rcu_preempt_cpu_has_callbacks(cpu);
}
static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
@@ -2027,9 +2259,10 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
rdp->qlen_lazy = 0;
rdp->qlen = 0;
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
rdp->cpu = cpu;
rdp->rsp = rsp;
@@ -2057,7 +2290,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->blimit = blimit;
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_NESTING;
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
atomic_set(&rdp->dynticks->dynticks,
(atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
rcu_prepare_for_idle_init(cpu);
@@ -2139,16 +2372,18 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
* touch any data without introducing corruption. We send the
* dying CPU's callbacks to an arbitrarily chosen online CPU.
*/
rcu_send_cbs_to_online(&rcu_bh_state);
rcu_send_cbs_to_online(&rcu_sched_state);
rcu_preempt_send_cbs_to_online();
rcu_cleanup_dying_cpu(&rcu_bh_state);
rcu_cleanup_dying_cpu(&rcu_sched_state);
rcu_preempt_cleanup_dying_cpu();
rcu_cleanup_after_idle(cpu);
break;
case CPU_DEAD:
case CPU_DEAD_FROZEN:
case CPU_UP_CANCELED:
case CPU_UP_CANCELED_FROZEN:
rcu_offline_cpu(cpu);
rcu_cleanup_dead_cpu(cpu, &rcu_bh_state);
rcu_cleanup_dead_cpu(cpu, &rcu_sched_state);
rcu_preempt_cleanup_dead_cpu(cpu);
break;
default:
break;

27
kernel/rcutree.h
View File

@@ -239,6 +239,12 @@ struct rcu_data {
bool preemptible; /* Preemptible RCU? */
struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
unsigned long grpmask; /* Mask to apply to leaf qsmask. */
#ifdef CONFIG_RCU_CPU_STALL_INFO
unsigned long ticks_this_gp; /* The number of scheduling-clock */
/* ticks this CPU has handled */
/* during and after the last grace */
/* period it is aware of. */
#endif /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
/* 2) batch handling */
/*
@@ -265,7 +271,8 @@ struct rcu_data {
*/
struct rcu_head *nxtlist;
struct rcu_head **nxttail[RCU_NEXT_SIZE];
long qlen; /* # of queued callbacks */
long qlen_lazy; /* # of lazy queued callbacks */
long qlen; /* # of queued callbacks, incl lazy */
long qlen_last_fqs_check;
/* qlen at last check for QS forcing */
unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */
@@ -282,7 +289,6 @@ struct rcu_data {
/* 4) reasons this CPU needed to be kicked by force_quiescent_state */
unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */
unsigned long offline_fqs; /* Kicked due to being offline. */
unsigned long resched_ipi; /* Sent a resched IPI. */
/* 5) __rcu_pending() statistics. */
unsigned long n_rcu_pending; /* rcu_pending() calls since boot. */
@@ -313,12 +319,6 @@ struct rcu_data {
#else
#define RCU_STALL_DELAY_DELTA 0
#endif
#define RCU_SECONDS_TILL_STALL_CHECK (CONFIG_RCU_CPU_STALL_TIMEOUT * HZ + \
RCU_STALL_DELAY_DELTA)
/* for rsp->jiffies_stall */
#define RCU_SECONDS_TILL_STALL_RECHECK (3 * RCU_SECONDS_TILL_STALL_CHECK + 30)
/* for rsp->jiffies_stall */
#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
/* to take at least one */
/* scheduling clock irq */
@@ -438,8 +438,8 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
struct rcu_node *rnp,
struct rcu_data *rdp);
static void rcu_preempt_offline_cpu(int cpu);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_preempt_cleanup_dead_cpu(int cpu);
static void rcu_preempt_check_callbacks(int cpu);
static void rcu_preempt_process_callbacks(void);
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
@@ -448,9 +448,9 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
bool wake);
#endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */
static int rcu_preempt_pending(int cpu);
static int rcu_preempt_needs_cpu(int cpu);
static int rcu_preempt_cpu_has_callbacks(int cpu);
static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
static void rcu_preempt_send_cbs_to_online(void);
static void rcu_preempt_cleanup_dying_cpu(void);
static void __init __rcu_init_preempt(void);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
@@ -471,5 +471,10 @@ static void __cpuinit rcu_prepare_kthreads(int cpu);
static void rcu_prepare_for_idle_init(int cpu);
static void rcu_cleanup_after_idle(int cpu);
static void rcu_prepare_for_idle(int cpu);
static void print_cpu_stall_info_begin(void);
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
static void print_cpu_stall_info_end(void);
static void zero_cpu_stall_ticks(struct rcu_data *rdp);
static void increment_cpu_stall_ticks(void);
#endif /* #ifndef RCU_TREE_NONCORE */

450
kernel/rcutree_plugin.h
View File

@@ -25,7 +25,6 @@
*/
#include <linux/delay.h>
#include <linux/stop_machine.h>
#define RCU_KTHREAD_PRIO 1
@@ -63,7 +62,10 @@ static void __init rcu_bootup_announce_oddness(void)
printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
#endif
#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n");
printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
#endif
#if NUM_RCU_LVL_4 != 0
printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");
@@ -490,6 +492,31 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp)
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
#ifdef CONFIG_RCU_CPU_STALL_INFO
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
}
static void rcu_print_task_stall_end(void)
{
printk(KERN_CONT "\n");
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
}
static void rcu_print_task_stall_end(void)
{
}
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each.
@@ -501,12 +528,14 @@ static int rcu_print_task_stall(struct rcu_node *rnp)
if (!rcu_preempt_blocked_readers_cgp(rnp))
return 0;
rcu_print_task_stall_begin(rnp);
t = list_entry(rnp->gp_tasks,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
printk(" P%d", t->pid);
printk(KERN_CONT " P%d", t->pid);
ndetected++;
}
rcu_print_task_stall_end();
return ndetected;
}
@@ -581,7 +610,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
* absolutely necessary, but this is a good performance/complexity
* tradeoff.
*/
if (rcu_preempt_blocked_readers_cgp(rnp))
if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
retval |= RCU_OFL_TASKS_NORM_GP;
if (rcu_preempted_readers_exp(rnp))
retval |= RCU_OFL_TASKS_EXP_GP;
@@ -618,16 +647,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
return retval;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Do CPU-offline processing for preemptible RCU.
*/
static void rcu_preempt_offline_cpu(int cpu)
static void rcu_preempt_cleanup_dead_cpu(int cpu)
{
__rcu_offline_cpu(cpu, &rcu_preempt_state);
rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state);
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Check for a quiescent state from the current CPU. When a task blocks,
* the task is recorded in the corresponding CPU's rcu_node structure,
@@ -671,10 +700,24 @@ static void rcu_preempt_do_callbacks(void)
*/
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_preempt_state);
__call_rcu(head, func, &rcu_preempt_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu);
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*/
void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_preempt_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
@@ -688,6 +731,10 @@ EXPORT_SYMBOL_GPL(call_rcu);
*/
void synchronize_rcu(void)
{
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
!lock_is_held(&rcu_lock_map) &&
!lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
if (!rcu_scheduler_active)
return;
wait_rcu_gp(call_rcu);
@@ -788,10 +835,22 @@ sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
}
/*
* Wait for an rcu-preempt grace period, but expedite it. The basic idea
* is to invoke synchronize_sched_expedited() to push all the tasks to
* the ->blkd_tasks lists and wait for this list to drain.
/**
* synchronize_rcu_expedited - Brute-force RCU grace period
*
* Wait for an RCU-preempt grace period, but expedite it. The basic
* idea is to invoke synchronize_sched_expedited() to push all the tasks to
* the ->blkd_tasks lists and wait for this list to drain. This consumes
* significant time on all CPUs and is unfriendly to real-time workloads,
* so is thus not recommended for any sort of common-case code.
* In fact, if you are using synchronize_rcu_expedited() in a loop,
* please restructure your code to batch your updates, and then Use a
* single synchronize_rcu() instead.
*
* Note that it is illegal to call this function while holding any lock
* that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
* to call this function from a CPU-hotplug notifier. Failing to observe
* these restriction will result in deadlock.
*/
void synchronize_rcu_expedited(void)
{
@@ -869,9 +928,9 @@ static int rcu_preempt_pending(int cpu)
}
/*
* Does preemptible RCU need the CPU to stay out of dynticks mode?
* Does preemptible RCU have callbacks on this CPU?
*/
static int rcu_preempt_needs_cpu(int cpu)
static int rcu_preempt_cpu_has_callbacks(int cpu)
{
return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
}
@@ -894,11 +953,12 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
}
/*
* Move preemptible RCU's callbacks from dying CPU to other online CPU.
* Move preemptible RCU's callbacks from dying CPU to other online CPU
* and record a quiescent state.
*/
static void rcu_preempt_send_cbs_to_online(void)
static void rcu_preempt_cleanup_dying_cpu(void)
{
rcu_send_cbs_to_online(&rcu_preempt_state);
rcu_cleanup_dying_cpu(&rcu_preempt_state);
}
/*
@@ -1034,16 +1094,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
return 0;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptible RCU does not exist, it never needs CPU-offline
* processing.
*/
static void rcu_preempt_offline_cpu(int cpu)
static void rcu_preempt_cleanup_dead_cpu(int cpu)
{
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptible RCU does not exist, it never has any callbacks
* to check.
@@ -1060,6 +1120,22 @@ static void rcu_preempt_process_callbacks(void)
{
}
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*
* Because there is no preemptible RCU, we use RCU-sched instead.
*/
void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_sched_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/*
* Wait for an rcu-preempt grace period, but make it happen quickly.
* But because preemptible RCU does not exist, map to rcu-sched.
@@ -1093,9 +1169,9 @@ static int rcu_preempt_pending(int cpu)
}
/*
* Because preemptible RCU does not exist, it never needs any CPU.
* Because preemptible RCU does not exist, it never has callbacks
*/
static int rcu_preempt_needs_cpu(int cpu)
static int rcu_preempt_cpu_has_callbacks(int cpu)
{
return 0;
}
@@ -1119,9 +1195,9 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
}
/*
* Because there is no preemptible RCU, there are no callbacks to move.
* Because there is no preemptible RCU, there is no cleanup to do.
*/
static void rcu_preempt_send_cbs_to_online(void)
static void rcu_preempt_cleanup_dying_cpu(void)
{
}
@@ -1823,132 +1899,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifndef CONFIG_SMP
void synchronize_sched_expedited(void)
{
cond_resched();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
#else /* #ifndef CONFIG_SMP */
static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
static int synchronize_sched_expedited_cpu_stop(void *data)
{
/*
* There must be a full memory barrier on each affected CPU
* between the time that try_stop_cpus() is called and the
* time that it returns.
*
* In the current initial implementation of cpu_stop, the
* above condition is already met when the control reaches
* this point and the following smp_mb() is not strictly
* necessary. Do smp_mb() anyway for documentation and
* robustness against future implementation changes.
*/
smp_mb(); /* See above comment block. */
return 0;
}
/*
* Wait for an rcu-sched grace period to elapse, but use "big hammer"
* approach to force grace period to end quickly. This consumes
* significant time on all CPUs, and is thus not recommended for
* any sort of common-case code.
*
* Note that it is illegal to call this function while holding any
* lock that is acquired by a CPU-hotplug notifier. Failing to
* observe this restriction will result in deadlock.
*
* This implementation can be thought of as an application of ticket
* locking to RCU, with sync_sched_expedited_started and
* sync_sched_expedited_done taking on the roles of the halves
* of the ticket-lock word. Each task atomically increments
* sync_sched_expedited_started upon entry, snapshotting the old value,
* then attempts to stop all the CPUs. If this succeeds, then each
* CPU will have executed a context switch, resulting in an RCU-sched
* grace period. We are then done, so we use atomic_cmpxchg() to
* update sync_sched_expedited_done to match our snapshot -- but
* only if someone else has not already advanced past our snapshot.
*
* On the other hand, if try_stop_cpus() fails, we check the value
* of sync_sched_expedited_done. If it has advanced past our
* initial snapshot, then someone else must have forced a grace period
* some time after we took our snapshot. In this case, our work is
* done for us, and we can simply return. Otherwise, we try again,
* but keep our initial snapshot for purposes of checking for someone
* doing our work for us.
*
* If we fail too many times in a row, we fall back to synchronize_sched().
*/
void synchronize_sched_expedited(void)
{
int firstsnap, s, snap, trycount = 0;
/* Note that atomic_inc_return() implies full memory barrier. */
firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
get_online_cpus();
/*
* Each pass through the following loop attempts to force a
* context switch on each CPU.
*/
while (try_stop_cpus(cpu_online_mask,
synchronize_sched_expedited_cpu_stop,
NULL) == -EAGAIN) {
put_online_cpus();
/* No joy, try again later. Or just synchronize_sched(). */
if (trycount++ < 10)
udelay(trycount * num_online_cpus());
else {
synchronize_sched();
return;
}
/* Check to see if someone else did our work for us. */
s = atomic_read(&sync_sched_expedited_done);
if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
smp_mb(); /* ensure test happens before caller kfree */
return;
}
/*
* Refetching sync_sched_expedited_started allows later
* callers to piggyback on our grace period. We subtract
* 1 to get the same token that the last incrementer got.
* We retry after they started, so our grace period works
* for them, and they started after our first try, so their
* grace period works for us.
*/
get_online_cpus();
snap = atomic_read(&sync_sched_expedited_started);
smp_mb(); /* ensure read is before try_stop_cpus(). */
}
/*
* Everyone up to our most recent fetch is covered by our grace
* period. Update the counter, but only if our work is still
* relevant -- which it won't be if someone who started later
* than we did beat us to the punch.
*/
do {
s = atomic_read(&sync_sched_expedited_done);
if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
smp_mb(); /* ensure test happens before caller kfree */
break;
}
} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
#endif /* #else #ifndef CONFIG_SMP */
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
@@ -1981,7 +1931,7 @@ static void rcu_cleanup_after_idle(int cpu)
}
/*
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=y,
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
* is nothing.
*/
static void rcu_prepare_for_idle(int cpu)
@@ -2015,6 +1965,9 @@ static void rcu_prepare_for_idle(int cpu)
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
* system. And if you are -that- concerned about energy efficiency,
* just power the system down and be done with it!
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
* permitted to sleep in dyntick-idle mode with only lazy RCU
* callbacks pending. Setting this too high can OOM your system.
*
* The values below work well in practice. If future workloads require
* adjustment, they can be converted into kernel config parameters, though
@@ -2023,11 +1976,13 @@ static void rcu_prepare_for_idle(int cpu)
#define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */
#define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */
#define RCU_IDLE_GP_DELAY 6 /* Roughly one grace period. */
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
static DEFINE_PER_CPU(int, rcu_dyntick_drain);
static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
static DEFINE_PER_CPU(struct hrtimer, rcu_idle_gp_timer);
static ktime_t rcu_idle_gp_wait;
static ktime_t rcu_idle_gp_wait; /* If some non-lazy callbacks. */
static ktime_t rcu_idle_lazy_gp_wait; /* If only lazy callbacks. */
/*
* Allow the CPU to enter dyntick-idle mode if either: (1) There are no
@@ -2047,6 +2002,48 @@ int rcu_needs_cpu(int cpu)
return per_cpu(rcu_dyntick_holdoff, cpu) == jiffies;
}
/*
* Does the specified flavor of RCU have non-lazy callbacks pending on
* the specified CPU? Both RCU flavor and CPU are specified by the
* rcu_data structure.
*/
static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
{
return rdp->qlen != rdp->qlen_lazy;
}
#ifdef CONFIG_TREE_PREEMPT_RCU
/*
* Are there non-lazy RCU-preempt callbacks? (There cannot be if there
* is no RCU-preempt in the kernel.)
*/
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
return __rcu_cpu_has_nonlazy_callbacks(rdp);
}
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
return 0;
}
#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
/*
* Does any flavor of RCU have non-lazy callbacks on the specified CPU?
*/
static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
{
return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
__rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
}
/*
* Timer handler used to force CPU to start pushing its remaining RCU
* callbacks in the case where it entered dyntick-idle mode with callbacks
@@ -2074,6 +2071,8 @@ static void rcu_prepare_for_idle_init(int cpu)
unsigned int upj = jiffies_to_usecs(RCU_IDLE_GP_DELAY);
rcu_idle_gp_wait = ns_to_ktime(upj * (u64)1000);
upj = jiffies_to_usecs(RCU_IDLE_LAZY_GP_DELAY);
rcu_idle_lazy_gp_wait = ns_to_ktime(upj * (u64)1000);
firsttime = 0;
}
}
@@ -2109,10 +2108,6 @@ static void rcu_cleanup_after_idle(int cpu)
*/
static void rcu_prepare_for_idle(int cpu)
{
unsigned long flags;
local_irq_save(flags);
/*
* If there are no callbacks on this CPU, enter dyntick-idle mode.
* Also reset state to avoid prejudicing later attempts.
@@ -2120,7 +2115,6 @@ static void rcu_prepare_for_idle(int cpu)
if (!rcu_cpu_has_callbacks(cpu)) {
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
per_cpu(rcu_dyntick_drain, cpu) = 0;
local_irq_restore(flags);
trace_rcu_prep_idle("No callbacks");
return;
}
@@ -2130,7 +2124,6 @@ static void rcu_prepare_for_idle(int cpu)
* refrained from disabling the scheduling-clock tick.
*/
if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) {
local_irq_restore(flags);
trace_rcu_prep_idle("In holdoff");
return;
}
@@ -2140,18 +2133,22 @@ static void rcu_prepare_for_idle(int cpu)
/* First time through, initialize the counter. */
per_cpu(rcu_dyntick_drain, cpu) = RCU_IDLE_FLUSHES;
} else if (per_cpu(rcu_dyntick_drain, cpu) <= RCU_IDLE_OPT_FLUSHES &&
!rcu_pending(cpu)) {
!rcu_pending(cpu) &&
!local_softirq_pending()) {
/* Can we go dyntick-idle despite still having callbacks? */
trace_rcu_prep_idle("Dyntick with callbacks");
per_cpu(rcu_dyntick_drain, cpu) = 0;
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
rcu_idle_gp_wait, HRTIMER_MODE_REL);
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
if (rcu_cpu_has_nonlazy_callbacks(cpu))
hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
rcu_idle_gp_wait, HRTIMER_MODE_REL);
else
hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
rcu_idle_lazy_gp_wait, HRTIMER_MODE_REL);
return; /* Nothing more to do immediately. */
} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
/* We have hit the limit, so time to give up. */
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
local_irq_restore(flags);
trace_rcu_prep_idle("Begin holdoff");
invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
return;
@@ -2163,23 +2160,17 @@ static void rcu_prepare_for_idle(int cpu)
*/
#ifdef CONFIG_TREE_PREEMPT_RCU
if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
local_irq_restore(flags);
rcu_preempt_qs(cpu);
force_quiescent_state(&rcu_preempt_state, 0);
local_irq_save(flags);
}
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
local_irq_restore(flags);
rcu_sched_qs(cpu);
force_quiescent_state(&rcu_sched_state, 0);
local_irq_save(flags);
}
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
local_irq_restore(flags);
rcu_bh_qs(cpu);
force_quiescent_state(&rcu_bh_state, 0);
local_irq_save(flags);
}
/*
@@ -2187,13 +2178,124 @@ static void rcu_prepare_for_idle(int cpu)
* So try forcing the callbacks through the grace period.
*/
if (rcu_cpu_has_callbacks(cpu)) {
local_irq_restore(flags);
trace_rcu_prep_idle("More callbacks");
invoke_rcu_core();
} else {
local_irq_restore(flags);
} else
trace_rcu_prep_idle("Callbacks drained");
}
}
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
#ifdef CONFIG_RCU_CPU_STALL_INFO
#ifdef CONFIG_RCU_FAST_NO_HZ
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu);
sprintf(cp, "drain=%d %c timer=%lld",
per_cpu(rcu_dyntick_drain, cpu),
per_cpu(rcu_dyntick_holdoff, cpu) == jiffies ? 'H' : '.',
hrtimer_active(hrtp)
? ktime_to_us(hrtimer_get_remaining(hrtp))
: -1);
}
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
}
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
printk(KERN_CONT "\n");
}
/*
* Print out diagnostic information for the specified stalled CPU.
*
* If the specified CPU is aware of the current RCU grace period
* (flavor specified by rsp), then print the number of scheduling
* clock interrupts the CPU has taken during the time that it has
* been aware. Otherwise, print the number of RCU grace periods
* that this CPU is ignorant of, for example, "1" if the CPU was
* aware of the previous grace period.
*
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
*/
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
char fast_no_hz[72];
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_dynticks *rdtp = rdp->dynticks;
char *ticks_title;
unsigned long ticks_value;
if (rsp->gpnum == rdp->gpnum) {
ticks_title = "ticks this GP";
ticks_value = rdp->ticks_this_gp;
} else {
ticks_title = "GPs behind";
ticks_value = rsp->gpnum - rdp->gpnum;
}
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
cpu, ticks_value, ticks_title,
atomic_read(&rdtp->dynticks) & 0xfff,
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
fast_no_hz);
}
/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
printk(KERN_ERR "\t");
}
/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
rdp->ticks_this_gp = 0;
}
/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
__get_cpu_var(rcu_sched_data).ticks_this_gp++;
__get_cpu_var(rcu_bh_data).ticks_this_gp++;
#ifdef CONFIG_TREE_PREEMPT_RCU
__get_cpu_var(rcu_preempt_data).ticks_this_gp++;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
static void print_cpu_stall_info_begin(void)
{
printk(KERN_CONT " {");
}
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
printk(KERN_CONT " %d", cpu);
}
static void print_cpu_stall_info_end(void)
{
printk(KERN_CONT "} ");
}
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
}
static void increment_cpu_stall_ticks(void)
{
}
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */

12
kernel/rcutree_trace.c
View File

@@ -72,9 +72,9 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks->dynticks_nesting,
rdp->dynticks->dynticks_nmi_nesting,
rdp->dynticks_fqs);
seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
seq_printf(m, " ql=%ld qs=%c%c%c%c",
rdp->qlen,
seq_printf(m, " of=%lu", rdp->offline_fqs);
seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c",
rdp->qlen_lazy, rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
@@ -144,8 +144,8 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks->dynticks_nesting,
rdp->dynticks->dynticks_nmi_nesting,
rdp->dynticks_fqs);
seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen,
seq_printf(m, ",%lu", rdp->offline_fqs);
seq_printf(m, ",%ld,%ld,\"%c%c%c%c\"", rdp->qlen_lazy, rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
@@ -168,7 +168,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
{
seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\",");
seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
seq_puts(m, "\"of\",\"qll\",\"ql\",\"qs\"");
#ifdef CONFIG_RCU_BOOST
seq_puts(m, "\"kt\",\"ktl\"");
#endif /* #ifdef CONFIG_RCU_BOOST */

33
kernel/srcu.c
View File

@@ -172,6 +172,12 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
{
int idx;
rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
!lock_is_held(&rcu_bh_lock_map) &&
!lock_is_held(&rcu_lock_map) &&
!lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
idx = sp->completed;
mutex_lock(&sp->mutex);
@@ -280,19 +286,26 @@ void synchronize_srcu(struct srcu_struct *sp)
EXPORT_SYMBOL_GPL(synchronize_srcu);
/**
* synchronize_srcu_expedited - like synchronize_srcu, but less patient
* synchronize_srcu_expedited - Brute-force SRCU grace period
* @sp: srcu_struct with which to synchronize.
*
* Flip the completed counter, and wait for the old count to drain to zero.
* As with classic RCU, the updater must use some separate means of
* synchronizing concurrent updates. Can block; must be called from
* process context.
* Wait for an SRCU grace period to elapse, but use a "big hammer"
* approach to force the grace period to end quickly. This consumes
* significant time on all CPUs and is unfriendly to real-time workloads,
* so is thus not recommended for any sort of common-case code. In fact,
* if you are using synchronize_srcu_expedited() in a loop, please
* restructure your code to batch your updates, and then use a single
* synchronize_srcu() instead.
*
* Note that it is illegal to call synchronize_srcu_expedited()
* from the corresponding SRCU read-side critical section; doing so
* will result in deadlock. However, it is perfectly legal to call
* synchronize_srcu_expedited() on one srcu_struct from some other
* srcu_struct's read-side critical section.
* Note that it is illegal to call this function while holding any lock
* that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
* to call this function from a CPU-hotplug notifier. Failing to observe
* these restriction will result in deadlock. It is also illegal to call
* synchronize_srcu_expedited() from the corresponding SRCU read-side
* critical section; doing so will result in deadlock. However, it is
* perfectly legal to call synchronize_srcu_expedited() on one srcu_struct
* from some other srcu_struct's read-side critical section, as long as
* the resulting graph of srcu_structs is acyclic.
*/
void synchronize_srcu_expedited(struct srcu_struct *sp)
{