fix for account_group_exec_runtime(), make sure ->signal can't be freed under rq->lock (ad474cac) · Commits · 戴 / test

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:

Oleg Nesterov <oleg@redhat.com> Acked-by:

Peter Zijlstra <peterz@infradead.org> Signed-off-by:

Ingo Molnar <mingo@elte.hu> Reported-by:

Doug Chapman <doug.chapman@hp.com>

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)
		{

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