linux-kernel - [tip:sched/core] sched: Check TASK_DEAD rather than EXIT_DEAD in schedule

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Date:	Wed, 27 Nov 2013 06:10:30 -0800
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	David.Laight@...LAB.COM, geert@...ux-m68k.org,
	akpm@...ux-foundation.org, tj@...nel.org, tglx@...utronix.de,
	oleg@...hat.com
Subject: [tip:sched/core] sched:
  Check TASK_DEAD rather than EXIT_DEAD in schedule_debug()

Commit-ID:  192301e70af3f6803c6354a464ebfa742da738ae
Gitweb:     http://git.kernel.org/tip/192301e70af3f6803c6354a464ebfa742da738ae
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Wed, 13 Nov 2013 16:45:38 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 27 Nov 2013 13:50:53 +0100

sched: Check TASK_DEAD rather than EXIT_DEAD in schedule_debug()

schedule_debug() ignores in_atomic() if prev->exit_state != 0.
This is not what we want, ->exit_state is set by exit_notify()
but we should complain until the task does the last schedule()
in TASK_DEAD.

See also 7407251a0e2e "PF_DEAD cleanup", I think this ancient
commit explains why schedule() had to rely on ->exit_state,
until that commit exit_notify() disabled preemption and set
PF_DEAD which was used to detect the exiting task.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Cc: David Laight <David.Laight@...LAB.COM>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/20131113154538.GB15810@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 687985b..19db8f3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2414,10 +2414,10 @@ static inline void schedule_debug(struct task_struct *prev)
 {
 	/*
 	 * Test if we are atomic. Since do_exit() needs to call into
-	 * schedule() atomically, we ignore that path for now.
-	 * Otherwise, whine if we are scheduling when we should not be.
+	 * schedule() atomically, we ignore that path. Otherwise whine
+	 * if we are scheduling when we should not.
 	 */
-	if (unlikely(in_atomic_preempt_off() && !prev->exit_state))
+	if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD))
 		__schedule_bug(prev);
 	rcu_sleep_check();
 
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