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sched/core: Introduce set_special_state()

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Gaurav reported a perceived problem with TASK_PARKED, which turned out
to be a broken wait-loop pattern in __kthread_parkme(), but the
reported issue can (and does) in fact happen for states that do not do
condition based sleeps.

When the 'current->state = TASK_RUNNING' store of a previous
(concurrent) try_to_wake_up() collides with the setting of a 'special'
sleep state, we can loose the sleep state.

Normal condition based wait-loops are immune to this problem, but for
sleep states that are not condition based are subject to this problem.

There already is a fix for TASK_DEAD. Abstract that and also apply it
to TASK_STOPPED and TASK_TRACED, both of which are also without
condition based wait-loop.

Reported-by: Gaurav Kohli <gkohli@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2018-04-30 14:51:01 +02:00
committed by Ingo Molnar
parent 85f1abe001
commit b5bf9a90bb
4 changed files with 62 additions and 24 deletions
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17
kernel/sched/core.c
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@@ -3508,23 +3508,8 @@ static void __sched notrace __schedule(bool preempt)
void __noreturn do_task_dead(void)
{
/*
* The setting of TASK_RUNNING by try_to_wake_up() may be delayed
* when the following two conditions become true.
* - There is race condition of mmap_sem (It is acquired by
* exit_mm()), and
* - SMI occurs before setting TASK_RUNINNG.
* (or hypervisor of virtual machine switches to other guest)
* As a result, we may become TASK_RUNNING after becoming TASK_DEAD
*
* To avoid it, we have to wait for releasing tsk->pi_lock which
* is held by try_to_wake_up()
*/
raw_spin_lock_irq(&current->pi_lock);
raw_spin_unlock_irq(&current->pi_lock);
/* Causes final put_task_struct in finish_task_switch(): */
__set_current_state(TASK_DEAD);
set_special_state(TASK_DEAD);
/* Tell freezer to ignore us: */
current->flags |= PF_NOFREEZE;