linux-kernel - [PATCH 1/1] sched: Check TASK_DEAD rather than EXIT_DEAD in schedule

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Message-ID: <20131113154538.GB15810@redhat.com>
Date:	Wed, 13 Nov 2013 16:45:38 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Laight <David.Laight@...LAB.COM>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Ingo Molnar <mingo@...nel.org>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] 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>
---
 kernel/sched/core.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5ac63c9..7184357 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2287,10 +2287,10 @@ 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();
 
-- 
1.5.5.1


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