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

Browse Source 
Pull scheduler fixes from Ingo Molnar:

 - Apply a number of membarrier related fixes and cleanups, which fixes
   a use-after-free race in the membarrier code

 - Introduce proper RCU protection for tasks on the runqueue - to get
   rid of the subtle task_rcu_dereference() interface that was easy to
   get wrong

 - Misc fixes, but also an EAS speedup

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Avoid redundant EAS calculation
  sched/core: Remove double update_max_interval() call on CPU startup
  sched/core: Fix preempt_schedule() interrupt return comment
  sched/fair: Fix -Wunused-but-set-variable warnings
  sched/core: Fix migration to invalid CPU in __set_cpus_allowed_ptr()
  sched/membarrier: Return -ENOMEM to userspace on memory allocation failure
  sched/membarrier: Skip IPIs when mm->mm_users == 1
  selftests, sched/membarrier: Add multi-threaded test
  sched/membarrier: Fix p->mm->membarrier_state racy load
  sched/membarrier: Call sync_core only before usermode for same mm
  sched/membarrier: Remove redundant check
  sched/membarrier: Fix private expedited registration check
  tasks, sched/core: RCUify the assignment of rq->curr
  tasks, sched/core: With a grace period after finish_task_switch(), remove unnecessary code
  tasks, sched/core: Ensure tasks are available for a grace period after leaving the runqueue
  tasks: Add a count of task RCU users
  sched/core: Convert vcpu_is_preempted() from macro to an inline function
  sched/fair: Remove unused cfs_rq_clock_task() function
This commit is contained in:
Linus Torvalds
2019-09-28 12:39:07 -07:00
parent aefcf2f4b5 4892f51ad5
commit 9c5efe9ae7
17 changed files with 375 additions and 250 deletions
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28
kernel/sched/core.c
View File

@@ -1656,7 +1656,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
if (cpumask_equal(p->cpus_ptr, new_mask))
goto out;
if (!cpumask_intersects(new_mask, cpu_valid_mask)) {
dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
if (dest_cpu >= nr_cpu_ids) {
ret = -EINVAL;
goto out;
}
@@ -1677,7 +1678,6 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
if (cpumask_test_cpu(task_cpu(p), new_mask))
goto out;
dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
if (task_running(rq, p) || p->state == TASK_WAKING) {
struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */
@@ -3254,7 +3254,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
/* Task is done with its stack. */
put_task_stack(prev);
put_task_struct(prev);
put_task_struct_rcu_user(prev);
}
tick_nohz_task_switch();
@@ -3358,15 +3358,15 @@ context_switch(struct rq *rq, struct task_struct *prev,
else
prev->active_mm = NULL;
} else { // to user
membarrier_switch_mm(rq, prev->active_mm, next->mm);
/*
* sys_membarrier() requires an smp_mb() between setting
* rq->curr and returning to userspace.
* rq->curr / membarrier_switch_mm() and returning to userspace.
*
* The below provides this either through switch_mm(), or in
* case 'prev->active_mm == next->mm' through
* finish_task_switch()'s mmdrop().
*/
switch_mm_irqs_off(prev->active_mm, next->mm, next);
if (!prev->mm) { // from kernel
@@ -4042,7 +4042,11 @@ static void __sched notrace __schedule(bool preempt)
if (likely(prev != next)) {
rq->nr_switches++;
rq->curr = next;
/*
* RCU users of rcu_dereference(rq->curr) may not see
* changes to task_struct made by pick_next_task().
*/
RCU_INIT_POINTER(rq->curr, next);
/*
* The membarrier system call requires each architecture
* to have a full memory barrier after updating
@@ -4223,9 +4227,8 @@ static void __sched notrace preempt_schedule_common(void)
#ifdef CONFIG_PREEMPTION
/*
* this is the entry point to schedule() from in-kernel preemption
* off of preempt_enable. Kernel preemptions off return from interrupt
* occur there and call schedule directly.
* This is the entry point to schedule() from in-kernel preemption
* off of preempt_enable.
*/
asmlinkage __visible void __sched notrace preempt_schedule(void)
{
@@ -4296,7 +4299,7 @@ EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
#endif /* CONFIG_PREEMPTION */
/*
* this is the entry point to schedule() from kernel preemption
* This is the entry point to schedule() from kernel preemption
* off of irq context.
* Note, that this is called and return with irqs disabled. This will
* protect us against recursive calling from irq.
@@ -6069,7 +6072,8 @@ void init_idle(struct task_struct *idle, int cpu)
__set_task_cpu(idle, cpu);
rcu_read_unlock();
rq->curr = rq->idle = idle;
rq->idle = idle;
rcu_assign_pointer(rq->curr, idle);
idle->on_rq = TASK_ON_RQ_QUEUED;
#ifdef CONFIG_SMP
idle->on_cpu = 1;
@@ -6430,8 +6434,6 @@ int sched_cpu_activate(unsigned int cpu)
}
rq_unlock_irqrestore(rq, &rf);
update_max_interval();
return 0;
}

39
kernel/sched/fair.c
View File

@@ -749,7 +749,6 @@ void init_entity_runnable_average(struct sched_entity *se)
/* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
}
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);
static void attach_entity_cfs_rq(struct sched_entity *se);
/*
@@ -1603,7 +1602,7 @@ static void task_numa_compare(struct task_numa_env *env,
return;
rcu_read_lock();
cur = task_rcu_dereference(&dst_rq->curr);
cur = rcu_dereference(dst_rq->curr);
if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
cur = NULL;
@@ -4354,21 +4353,16 @@ static inline u64 sched_cfs_bandwidth_slice(void)
}
/*
* Replenish runtime according to assigned quota and update expiration time.
* We use sched_clock_cpu directly instead of rq->clock to avoid adding
* additional synchronization around rq->lock.
* Replenish runtime according to assigned quota. We use sched_clock_cpu
* directly instead of rq->clock to avoid adding additional synchronization
* around rq->lock.
*
* requires cfs_b->lock
*/
void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
{
u64 now;
if (cfs_b->quota == RUNTIME_INF)
return;
now = sched_clock_cpu(smp_processor_id());
cfs_b->runtime = cfs_b->quota;
if (cfs_b->quota != RUNTIME_INF)
cfs_b->runtime = cfs_b->quota;
}
static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
@@ -4376,15 +4370,6 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
return &tg->cfs_bandwidth;
}
/* rq->task_clock normalized against any time this cfs_rq has spent throttled */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
if (unlikely(cfs_rq->throttle_count))
return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
}
/* returns 0 on failure to allocate runtime */
static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
@@ -4476,7 +4461,6 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
cfs_rq->throttle_count--;
if (!cfs_rq->throttle_count) {
/* adjust cfs_rq_clock_task() */
cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
cfs_rq->throttled_clock_task;
@@ -4994,15 +4978,13 @@ static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
u64 overrun;
lockdep_assert_held(&cfs_b->lock);
if (cfs_b->period_active)
return;
cfs_b->period_active = 1;
overrun = hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
}
@@ -5080,11 +5062,6 @@ static inline bool cfs_bandwidth_used(void)
return false;
}
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
return rq_clock_task(rq_of(cfs_rq));
}
static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) {}
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; }
static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {}
@@ -6412,7 +6389,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
}
/* Evaluate the energy impact of using this CPU. */
if (max_spare_cap_cpu >= 0) {
if (max_spare_cap_cpu >= 0 && max_spare_cap_cpu != prev_cpu) {
cur_delta = compute_energy(p, max_spare_cap_cpu, pd);
cur_delta -= base_energy_pd;
if (cur_delta < best_delta) {

239
kernel/sched/membarrier.c
View File

@@ -30,10 +30,42 @@ static void ipi_mb(void *info)
smp_mb(); /* IPIs should be serializing but paranoid. */
}
static void ipi_sync_rq_state(void *info)
{
struct mm_struct *mm = (struct mm_struct *) info;
if (current->mm != mm)
return;
this_cpu_write(runqueues.membarrier_state,
atomic_read(&mm->membarrier_state));
/*
* Issue a memory barrier after setting
* MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to
* guarantee that no memory access following registration is reordered
* before registration.
*/
smp_mb();
}
void membarrier_exec_mmap(struct mm_struct *mm)
{
/*
* Issue a memory barrier before clearing membarrier_state to
* guarantee that no memory access prior to exec is reordered after
* clearing this state.
*/
smp_mb();
atomic_set(&mm->membarrier_state, 0);
/*
* Keep the runqueue membarrier_state in sync with this mm
* membarrier_state.
*/
this_cpu_write(runqueues.membarrier_state, 0);
}
static int membarrier_global_expedited(void)
{
int cpu;
bool fallback = false;
cpumask_var_t tmpmask;
if (num_online_cpus() == 1)
@@ -45,17 +77,11 @@ static int membarrier_global_expedited(void)
*/
smp_mb(); /* system call entry is not a mb. */
/*
* Expedited membarrier commands guarantee that they won't
* block, hence the GFP_NOWAIT allocation flag and fallback
* implementation.
*/
if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
/* Fallback for OOM. */
fallback = true;
}
if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
return -ENOMEM;
cpus_read_lock();
rcu_read_lock();
for_each_online_cpu(cpu) {
struct task_struct *p;
@@ -70,23 +96,28 @@ static int membarrier_global_expedited(void)
if (cpu == raw_smp_processor_id())
continue;
rcu_read_lock();
p = task_rcu_dereference(&cpu_rq(cpu)->curr);
if (p && p->mm && (atomic_read(&p->mm->membarrier_state) &
MEMBARRIER_STATE_GLOBAL_EXPEDITED)) {
if (!fallback)
__cpumask_set_cpu(cpu, tmpmask);
else
smp_call_function_single(cpu, ipi_mb, NULL, 1);
}
rcu_read_unlock();
}
if (!fallback) {
preempt_disable();
smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
preempt_enable();
free_cpumask_var(tmpmask);
if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) &
MEMBARRIER_STATE_GLOBAL_EXPEDITED))
continue;
/*
* Skip the CPU if it runs a kernel thread. The scheduler
* leaves the prior task mm in place as an optimization when
* scheduling a kthread.
*/
p = rcu_dereference(cpu_rq(cpu)->curr);
if (p->flags & PF_KTHREAD)
continue;
__cpumask_set_cpu(cpu, tmpmask);
}
rcu_read_unlock();
preempt_disable();
smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
preempt_enable();
free_cpumask_var(tmpmask);
cpus_read_unlock();
/*
@@ -101,22 +132,22 @@ static int membarrier_global_expedited(void)
static int membarrier_private_expedited(int flags)
{
int cpu;
bool fallback = false;
cpumask_var_t tmpmask;
struct mm_struct *mm = current->mm;
if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
return -EINVAL;
if (!(atomic_read(&current->mm->membarrier_state) &
if (!(atomic_read(&mm->membarrier_state) &
MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
return -EPERM;
} else {
if (!(atomic_read(&current->mm->membarrier_state) &
if (!(atomic_read(&mm->membarrier_state) &
MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
return -EPERM;
}
if (num_online_cpus() == 1)
if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1)
return 0;
/*
@@ -125,17 +156,11 @@ static int membarrier_private_expedited(int flags)
*/
smp_mb(); /* system call entry is not a mb. */
/*
* Expedited membarrier commands guarantee that they won't
* block, hence the GFP_NOWAIT allocation flag and fallback
* implementation.
*/
if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
/* Fallback for OOM. */
fallback = true;
}
if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
return -ENOMEM;
cpus_read_lock();
rcu_read_lock();
for_each_online_cpu(cpu) {
struct task_struct *p;
@@ -150,21 +175,17 @@ static int membarrier_private_expedited(int flags)
if (cpu == raw_smp_processor_id())
continue;
rcu_read_lock();
p = task_rcu_dereference(&cpu_rq(cpu)->curr);
if (p && p->mm == current->mm) {
if (!fallback)
__cpumask_set_cpu(cpu, tmpmask);
else
smp_call_function_single(cpu, ipi_mb, NULL, 1);
}
rcu_read_unlock();
}
if (!fallback) {
preempt_disable();
smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
preempt_enable();
free_cpumask_var(tmpmask);
p = rcu_dereference(cpu_rq(cpu)->curr);
if (p && p->mm == mm)
__cpumask_set_cpu(cpu, tmpmask);
}
rcu_read_unlock();
preempt_disable();
smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
preempt_enable();
free_cpumask_var(tmpmask);
cpus_read_unlock();
/*
@@ -177,32 +198,78 @@ static int membarrier_private_expedited(int flags)
return 0;
}
static int sync_runqueues_membarrier_state(struct mm_struct *mm)
{
int membarrier_state = atomic_read(&mm->membarrier_state);
cpumask_var_t tmpmask;
int cpu;
if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) {
this_cpu_write(runqueues.membarrier_state, membarrier_state);
/*
* For single mm user, we can simply issue a memory barrier
* after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the
* mm and in the current runqueue to guarantee that no memory
* access following registration is reordered before
* registration.
*/
smp_mb();
return 0;
}
if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
return -ENOMEM;
/*
* For mm with multiple users, we need to ensure all future
* scheduler executions will observe @mm's new membarrier
* state.
*/
synchronize_rcu();
/*
* For each cpu runqueue, if the task's mm match @mm, ensure that all
* @mm's membarrier state set bits are also set in in the runqueue's
* membarrier state. This ensures that a runqueue scheduling
* between threads which are users of @mm has its membarrier state
* updated.
*/
cpus_read_lock();
rcu_read_lock();
for_each_online_cpu(cpu) {
struct rq *rq = cpu_rq(cpu);
struct task_struct *p;
p = rcu_dereference(rq->curr);
if (p && p->mm == mm)
__cpumask_set_cpu(cpu, tmpmask);
}
rcu_read_unlock();
preempt_disable();
smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1);
preempt_enable();
free_cpumask_var(tmpmask);
cpus_read_unlock();
return 0;
}
static int membarrier_register_global_expedited(void)
{
struct task_struct *p = current;
struct mm_struct *mm = p->mm;
int ret;
if (atomic_read(&mm->membarrier_state) &
MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
return 0;
atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
if (atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1) {
/*
* For single mm user, single threaded process, we can
* simply issue a memory barrier after setting
* MEMBARRIER_STATE_GLOBAL_EXPEDITED to guarantee that
* no memory access following registration is reordered
* before registration.
*/
smp_mb();
} else {
/*
* For multi-mm user threads, we need to ensure all
* future scheduler executions will observe the new
* thread flag state for this mm.
*/
synchronize_rcu();
}
ret = sync_runqueues_membarrier_state(mm);
if (ret)
return ret;
atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
&mm->membarrier_state);
@@ -213,12 +280,15 @@ static int membarrier_register_private_expedited(int flags)
{
struct task_struct *p = current;
struct mm_struct *mm = p->mm;
int state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY;
int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,
set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED,
ret;
if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
return -EINVAL;
state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
ready_state =
MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
}
/*
@@ -226,20 +296,15 @@ static int membarrier_register_private_expedited(int flags)
* groups, which use the same mm. (CLONE_VM but not
* CLONE_THREAD).
*/
if (atomic_read(&mm->membarrier_state) & state)
if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state)
return 0;
atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state);
if (flags & MEMBARRIER_FLAG_SYNC_CORE)
atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE,
&mm->membarrier_state);
if (!(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)) {
/*
* Ensure all future scheduler executions will observe the
* new thread flag state for this process.
*/
synchronize_rcu();
}
atomic_or(state, &mm->membarrier_state);
set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE;
atomic_or(set_state, &mm->membarrier_state);
ret = sync_runqueues_membarrier_state(mm);
if (ret)
return ret;
atomic_or(ready_state, &mm->membarrier_state);
return 0;
}
@@ -253,8 +318,10 @@ static int membarrier_register_private_expedited(int flags)
* command specified does not exist, not available on the running
* kernel, or if the command argument is invalid, this system call
* returns -EINVAL. For a given command, with flags argument set to 0,
* this system call is guaranteed to always return the same value until
* reboot.
* if this system call returns -ENOSYS or -EINVAL, it is guaranteed to
* always return the same value until reboot. In addition, it can return
* -ENOMEM if there is not enough memory available to perform the system
* call.
*
* All memory accesses performed in program order from each targeted thread
* is guaranteed to be ordered with respect to sys_membarrier(). If we use

34
kernel/sched/sched.h
View File

@@ -911,6 +911,10 @@ struct rq {
atomic_t nr_iowait;
#ifdef CONFIG_MEMBARRIER
int membarrier_state;
#endif
#ifdef CONFIG_SMP
struct root_domain *rd;
struct sched_domain __rcu *sd;
@@ -2438,3 +2442,33 @@ static inline bool sched_energy_enabled(void)
static inline bool sched_energy_enabled(void) { return false; }
#endif /* CONFIG_ENERGY_MODEL && CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
#ifdef CONFIG_MEMBARRIER
/*
* The scheduler provides memory barriers required by membarrier between:
* - prior user-space memory accesses and store to rq->membarrier_state,
* - store to rq->membarrier_state and following user-space memory accesses.
* In the same way it provides those guarantees around store to rq->curr.
*/
static inline void membarrier_switch_mm(struct rq *rq,
struct mm_struct *prev_mm,
struct mm_struct *next_mm)
{
int membarrier_state;
if (prev_mm == next_mm)
return;
membarrier_state = atomic_read(&next_mm->membarrier_state);
if (READ_ONCE(rq->membarrier_state) == membarrier_state)
return;
WRITE_ONCE(rq->membarrier_state, membarrier_state);
}
#else
static inline void membarrier_switch_mm(struct rq *rq,
struct mm_struct *prev_mm,
struct mm_struct *next_mm)
{
}
#endif