fix for account_group_exec_runtime(), make sure ->signal can't be fre…

…ed 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: Oleg Nesterov <[email protected]> Acked-by: Peter Zijlstra <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> Reported-by: Doug Chapman <[email protected]>
vbatts · Nov 11, 2008 · ad474ca · ad474ca
1 parent 5ac5c4d
commit ad474ca
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diff --git a/include/linux/sched.h b/include/linux/sched.h
@@ -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)

diff --git a/kernel/exit.c b/kernel/exit.c
@@ -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);
 	}
 }

diff --git a/kernel/sched.c b/kernel/sched.c
@@ -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)
 {