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Commit ad474cac authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

fix for account_group_exec_runtime(), make sure ->signal can't be freed under rq->lock 



Impact: fix hang/crash on ia64 under high load

This is ugly, but the simplest patch by far.

Unlike other similar routines, account_group_exec_runtime() could be
called "implicitly" from within scheduler after exit_notify(). This
means we can race with the parent doing release_task(), we can't just
check ->signal != NULL.

Change __exit_signal() to do spin_unlock_wait(&task_rq(tsk)->lock)
before __cleanup_signal() to make sure ->signal can't be freed under
task_rq(tsk)->lock. Note that task_rq_unlock_wait() doesn't care
about the case when tsk changes cpu/rq under us, this should be OK.

Thanks to Ingo who nacked my previous buggy patch.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Reported-by: default avatarDoug Chapman <doug.chapman@hp.com>
parent 5ac5c4d6

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -247,6 +247,7 @@ extern void init_idle(struct task_struct *idle, int cpu); 
extern void init_idle_bootup_task(struct task_struct *idle);



extern int runqueue_is_locked(void);

extern void task_rq_unlock_wait(struct task_struct *p);



extern cpumask_t nohz_cpu_mask;

#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)

kernel/exit.c

+5 −0
Original line number Diff line number Diff line
@@ -141,6 +141,11 @@ static void __exit_signal(struct task_struct *tsk) 
	if (sig) {

		flush_sigqueue(&sig->shared_pending);

		taskstats_tgid_free(sig);

		/*

		 * Make sure ->signal can't go away under rq->lock,

		 * see account_group_exec_runtime().

		 */

		task_rq_unlock_wait(tsk);

		__cleanup_signal(sig);

	}

}

kernel/sched.c

+8 −0
Original line number Diff line number Diff line
@@ -969,6 +969,14 @@ static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags) 
	}

}



void task_rq_unlock_wait(struct task_struct *p)

{

	struct rq *rq = task_rq(p);



	smp_mb(); /* spin-unlock-wait is not a full memory barrier */

	spin_unlock_wait(&rq->lock);

}



static void __task_rq_unlock(struct rq *rq)

	__releases(rq->lock)

{