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Merge branches 'core-urgent-for-linus', 'perf-urgent-for-linus' and 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull RCU, perf, and scheduler fixes from Ingo Molnar.

The RCU fix is a revert for an optimization that could cause deadlocks.

One of the scheduler commits (164c33c6ad "sched: Fix fork() error path
to not crash") is correct but not complete (some architectures like Tile
are not covered yet) - the resulting additional fixes are still WIP and
Ingo did not want to delay these pending fixes.  See this thread on
lkml:

  [PATCH] fork: fix error handling in dup_task()

The perf fixes are just trivial oneliners.

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf kvm: Fix segfault with report and mixed guestmount use
  perf kvm: Fix regression with guest machine creation
  perf script: Fix format regression due to libtraceevent merge
  ring-buffer: Fix accounting of entries when removing pages
  ring-buffer: Fix crash due to uninitialized new_pages list head

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  MAINTAINERS/sched: Update scheduler file pattern
  sched/nohz: Rewrite and fix load-avg computation -- again
  sched: Fix fork() error path to not crash
This commit is contained in:
Linus Torvalds
2012-07-14 11:16:24 -07:00
parent fdb1335a82 40b3c43f04 25c037d64e 95c0d71dcb
commit ab93eb8216
17 changed files with 262 additions and 116 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
kernel/fork.c
View File

@@ -304,12 +304,17 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
}
err = arch_dup_task_struct(tsk, orig);
/*
* We defer looking at err, because we will need this setup
* for the clean up path to work correctly.
*/
tsk->stack = ti;
setup_thread_stack(tsk, orig);
if (err)
goto out;
tsk->stack = ti;
setup_thread_stack(tsk, orig);
clear_user_return_notifier(tsk);
clear_tsk_need_resched(tsk);
stackend = end_of_stack(tsk);

1
kernel/rcutree.c
View File

@@ -201,6 +201,7 @@ void rcu_note_context_switch(int cpu)
{
trace_rcu_utilization("Start context switch");
rcu_sched_qs(cpu);
rcu_preempt_note_context_switch(cpu);
trace_rcu_utilization("End context switch");
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);

1
kernel/rcutree.h
View File

@@ -444,6 +444,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work);
/* Forward declarations for rcutree_plugin.h */
static void rcu_bootup_announce(void);
long rcu_batches_completed(void);
static void rcu_preempt_note_context_switch(int cpu);
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,

14
kernel/rcutree_plugin.h
View File

@@ -153,7 +153,7 @@ static void rcu_preempt_qs(int cpu)
*
* Caller must disable preemption.
*/
void rcu_preempt_note_context_switch(void)
static void rcu_preempt_note_context_switch(int cpu)
{
struct task_struct *t = current;
unsigned long flags;
@@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void)
(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
/* Possibly blocking in an RCU read-side critical section. */
rdp = __this_cpu_ptr(rcu_preempt_state.rda);
rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
@@ -228,7 +228,7 @@ void rcu_preempt_note_context_switch(void)
* means that we continue to block the current grace period.
*/
local_irq_save(flags);
rcu_preempt_qs(smp_processor_id());
rcu_preempt_qs(cpu);
local_irq_restore(flags);
}
@@ -1001,6 +1001,14 @@ void rcu_force_quiescent_state(void)
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
* Because preemptible RCU does not exist, we never have to check for
* CPUs being in quiescent states.
*/
static void rcu_preempt_note_context_switch(int cpu)
{
}
/*
* Because preemptible RCU does not exist, there are never any preempted
* RCU readers.

278
kernel/sched/core.c
View File

@@ -2081,7 +2081,6 @@ context_switch(struct rq *rq, struct task_struct *prev,
#endif
/* Here we just switch the register state and the stack. */
rcu_switch_from(prev);
switch_to(prev, next, prev);
barrier();
@@ -2161,11 +2160,73 @@ unsigned long this_cpu_load(void)
}
/*
* Global load-average calculations
*
* We take a distributed and async approach to calculating the global load-avg
* in order to minimize overhead.
*
* The global load average is an exponentially decaying average of nr_running +
* nr_uninterruptible.
*
* Once every LOAD_FREQ:
*
* nr_active = 0;
* for_each_possible_cpu(cpu)
* nr_active += cpu_of(cpu)->nr_running + cpu_of(cpu)->nr_uninterruptible;
*
* avenrun[n] = avenrun[0] * exp_n + nr_active * (1 - exp_n)
*
* Due to a number of reasons the above turns in the mess below:
*
* - for_each_possible_cpu() is prohibitively expensive on machines with
* serious number of cpus, therefore we need to take a distributed approach
* to calculating nr_active.
*
* \Sum_i x_i(t) = \Sum_i x_i(t) - x_i(t_0) | x_i(t_0) := 0
* = \Sum_i { \Sum_j=1 x_i(t_j) - x_i(t_j-1) }
*
* So assuming nr_active := 0 when we start out -- true per definition, we
* can simply take per-cpu deltas and fold those into a global accumulate
* to obtain the same result. See calc_load_fold_active().
*
* Furthermore, in order to avoid synchronizing all per-cpu delta folding
* across the machine, we assume 10 ticks is sufficient time for every
* cpu to have completed this task.
*
* This places an upper-bound on the IRQ-off latency of the machine. Then
* again, being late doesn't loose the delta, just wrecks the sample.
*
* - cpu_rq()->nr_uninterruptible isn't accurately tracked per-cpu because
* this would add another cross-cpu cacheline miss and atomic operation
* to the wakeup path. Instead we increment on whatever cpu the task ran
* when it went into uninterruptible state and decrement on whatever cpu
* did the wakeup. This means that only the sum of nr_uninterruptible over
* all cpus yields the correct result.
*
* This covers the NO_HZ=n code, for extra head-aches, see the comment below.
*/
/* Variables and functions for calc_load */
static atomic_long_t calc_load_tasks;
static unsigned long calc_load_update;
unsigned long avenrun[3];
EXPORT_SYMBOL(avenrun);
EXPORT_SYMBOL(avenrun); /* should be removed */
/**
* get_avenrun - get the load average array
* @loads: pointer to dest load array
* @offset: offset to add
* @shift: shift count to shift the result left
*
* These values are estimates at best, so no need for locking.
*/
void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
{
loads[0] = (avenrun[0] + offset) << shift;
loads[1] = (avenrun[1] + offset) << shift;
loads[2] = (avenrun[2] + offset) << shift;
}
static long calc_load_fold_active(struct rq *this_rq)
{
@@ -2182,6 +2243,9 @@ static long calc_load_fold_active(struct rq *this_rq)
return delta;
}
/*
* a1 = a0 * e + a * (1 - e)
*/
static unsigned long
calc_load(unsigned long load, unsigned long exp, unsigned long active)
{
@@ -2193,30 +2257,118 @@ calc_load(unsigned long load, unsigned long exp, unsigned long active)
#ifdef CONFIG_NO_HZ
/*
* For NO_HZ we delay the active fold to the next LOAD_FREQ update.
* Handle NO_HZ for the global load-average.
*
* Since the above described distributed algorithm to compute the global
* load-average relies on per-cpu sampling from the tick, it is affected by
* NO_HZ.
*
* The basic idea is to fold the nr_active delta into a global idle-delta upon
* entering NO_HZ state such that we can include this as an 'extra' cpu delta
* when we read the global state.
*
* Obviously reality has to ruin such a delightfully simple scheme:
*
* - When we go NO_HZ idle during the window, we can negate our sample
* contribution, causing under-accounting.
*
* We avoid this by keeping two idle-delta counters and flipping them
* when the window starts, thus separating old and new NO_HZ load.
*
* The only trick is the slight shift in index flip for read vs write.
*
* 0s 5s 10s 15s
* +10 +10 +10 +10
* |-|-----------|-|-----------|-|-----------|-|
* r:0 0 1 1 0 0 1 1 0
* w:0 1 1 0 0 1 1 0 0
*
* This ensures we'll fold the old idle contribution in this window while
* accumlating the new one.
*
* - When we wake up from NO_HZ idle during the window, we push up our
* contribution, since we effectively move our sample point to a known
* busy state.
*
* This is solved by pushing the window forward, and thus skipping the
* sample, for this cpu (effectively using the idle-delta for this cpu which
* was in effect at the time the window opened). This also solves the issue
* of having to deal with a cpu having been in NOHZ idle for multiple
* LOAD_FREQ intervals.
*
* When making the ILB scale, we should try to pull this in as well.
*/
static atomic_long_t calc_load_tasks_idle;
static atomic_long_t calc_load_idle[2];
static int calc_load_idx;
void calc_load_account_idle(struct rq *this_rq)
static inline int calc_load_write_idx(void)
{
int idx = calc_load_idx;
/*
* See calc_global_nohz(), if we observe the new index, we also
* need to observe the new update time.
*/
smp_rmb();
/*
* If the folding window started, make sure we start writing in the
* next idle-delta.
*/
if (!time_before(jiffies, calc_load_update))
idx++;
return idx & 1;
}
static inline int calc_load_read_idx(void)
{
return calc_load_idx & 1;
}
void calc_load_enter_idle(void)
{
struct rq *this_rq = this_rq();
long delta;
/*
* We're going into NOHZ mode, if there's any pending delta, fold it
* into the pending idle delta.
*/
delta = calc_load_fold_active(this_rq);
if (delta)
atomic_long_add(delta, &calc_load_tasks_idle);
if (delta) {
int idx = calc_load_write_idx();
atomic_long_add(delta, &calc_load_idle[idx]);
}
}
void calc_load_exit_idle(void)
{
struct rq *this_rq = this_rq();
/*
* If we're still before the sample window, we're done.
*/
if (time_before(jiffies, this_rq->calc_load_update))
return;
/*
* We woke inside or after the sample window, this means we're already
* accounted through the nohz accounting, so skip the entire deal and
* sync up for the next window.
*/
this_rq->calc_load_update = calc_load_update;
if (time_before(jiffies, this_rq->calc_load_update + 10))
this_rq->calc_load_update += LOAD_FREQ;
}
static long calc_load_fold_idle(void)
{
int idx = calc_load_read_idx();
long delta = 0;
/*
* Its got a race, we don't care...
*/
if (atomic_long_read(&calc_load_tasks_idle))
delta = atomic_long_xchg(&calc_load_tasks_idle, 0);
if (atomic_long_read(&calc_load_idle[idx]))
delta = atomic_long_xchg(&calc_load_idle[idx], 0);
return delta;
}
@@ -2302,66 +2454,39 @@ static void calc_global_nohz(void)
{
long delta, active, n;
/*
* If we crossed a calc_load_update boundary, make sure to fold
* any pending idle changes, the respective CPUs might have
* missed the tick driven calc_load_account_active() update
* due to NO_HZ.
*/
delta = calc_load_fold_idle();
if (delta)
atomic_long_add(delta, &calc_load_tasks);
if (!time_before(jiffies, calc_load_update + 10)) {
/*
* Catch-up, fold however many we are behind still
*/
delta = jiffies - calc_load_update - 10;
n = 1 + (delta / LOAD_FREQ);
active = atomic_long_read(&calc_load_tasks);
active = active > 0 ? active * FIXED_1 : 0;
avenrun[0] = calc_load_n(avenrun[0], EXP_1, active, n);
avenrun[1] = calc_load_n(avenrun[1], EXP_5, active, n);
avenrun[2] = calc_load_n(avenrun[2], EXP_15, active, n);
calc_load_update += n * LOAD_FREQ;
}
/*
* It could be the one fold was all it took, we done!
* Flip the idle index...
*
* Make sure we first write the new time then flip the index, so that
* calc_load_write_idx() will see the new time when it reads the new
* index, this avoids a double flip messing things up.
*/
if (time_before(jiffies, calc_load_update + 10))
return;
/*
* Catch-up, fold however many we are behind still
*/
delta = jiffies - calc_load_update - 10;
n = 1 + (delta / LOAD_FREQ);
active = atomic_long_read(&calc_load_tasks);
active = active > 0 ? active * FIXED_1 : 0;
avenrun[0] = calc_load_n(avenrun[0], EXP_1, active, n);
avenrun[1] = calc_load_n(avenrun[1], EXP_5, active, n);
avenrun[2] = calc_load_n(avenrun[2], EXP_15, active, n);
calc_load_update += n * LOAD_FREQ;
}
#else
void calc_load_account_idle(struct rq *this_rq)
{
smp_wmb();
calc_load_idx++;
}
#else /* !CONFIG_NO_HZ */
static inline long calc_load_fold_idle(void)
{
return 0;
}
static inline long calc_load_fold_idle(void) { return 0; }
static inline void calc_global_nohz(void) { }
static void calc_global_nohz(void)
{
}
#endif
/**
* get_avenrun - get the load average array
* @loads: pointer to dest load array
* @offset: offset to add
* @shift: shift count to shift the result left
*
* These values are estimates at best, so no need for locking.
*/
void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
{
loads[0] = (avenrun[0] + offset) << shift;
loads[1] = (avenrun[1] + offset) << shift;
loads[2] = (avenrun[2] + offset) << shift;
}
#endif /* CONFIG_NO_HZ */
/*
* calc_load - update the avenrun load estimates 10 ticks after the
@@ -2369,11 +2494,18 @@ void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
*/
void calc_global_load(unsigned long ticks)
{
long active;
long active, delta;
if (time_before(jiffies, calc_load_update + 10))
return;
/*
* Fold the 'old' idle-delta to include all NO_HZ cpus.
*/
delta = calc_load_fold_idle();
if (delta)
atomic_long_add(delta, &calc_load_tasks);
active = atomic_long_read(&calc_load_tasks);
active = active > 0 ? active * FIXED_1 : 0;
@@ -2384,12 +2516,7 @@ void calc_global_load(unsigned long ticks)
calc_load_update += LOAD_FREQ;
/*
* Account one period with whatever state we found before
* folding in the nohz state and ageing the entire idle period.
*
* This avoids loosing a sample when we go idle between
* calc_load_account_active() (10 ticks ago) and now and thus
* under-accounting.
* In case we idled for multiple LOAD_FREQ intervals, catch up in bulk.
*/
calc_global_nohz();
}
@@ -2406,13 +2533,16 @@ static void calc_load_account_active(struct rq *this_rq)
return;
delta = calc_load_fold_active(this_rq);
delta += calc_load_fold_idle();
if (delta)
atomic_long_add(delta, &calc_load_tasks);
this_rq->calc_load_update += LOAD_FREQ;
}
/*
* End of global load-average stuff
*/
/*
* The exact cpuload at various idx values, calculated at every tick would be
* load = (2^idx - 1) / 2^idx * load + 1 / 2^idx * cur_load

1
kernel/sched/idle_task.c
View File

@@ -25,7 +25,6 @@ static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int fl
static struct task_struct *pick_next_task_idle(struct rq *rq)
{
schedstat_inc(rq, sched_goidle);
calc_load_account_idle(rq);
return rq->idle;
}

2
kernel/sched/sched.h
View File

@@ -942,8 +942,6 @@ static inline u64 sched_avg_period(void)
return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;
}
void calc_load_account_idle(struct rq *this_rq);
#ifdef CONFIG_SCHED_HRTICK
/*

2
kernel/time/tick-sched.c
View File

@@ -406,6 +406,7 @@ static void tick_nohz_stop_sched_tick(struct tick_sched *ts)
*/
if (!ts->tick_stopped) {
select_nohz_load_balancer(1);
calc_load_enter_idle();
ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
ts->tick_stopped = 1;
@@ -597,6 +598,7 @@ void tick_nohz_idle_exit(void)
account_idle_ticks(ticks);
#endif
calc_load_exit_idle();
touch_softlockup_watchdog();
/*
* Cancel the scheduled timer and restore the tick

6
kernel/trace/ring_buffer.c
View File

@@ -1075,6 +1075,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu)
rb_init_page(bpage->page);
INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
INIT_LIST_HEAD(&cpu_buffer->new_pages);
ret = rb_allocate_pages(cpu_buffer, nr_pages);
if (ret < 0)
@@ -1346,10 +1347,9 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
* If something was added to this page, it was full
* since it is not the tail page. So we deduct the
* bytes consumed in ring buffer from here.
* No need to update overruns, since this page is
* deleted from ring buffer and its entries are
* already accounted for.
* Increment overrun to account for the lost events.
*/
local_add(page_entries, &cpu_buffer->overrun);
local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
}