Commit 29b88492 authored Sep 29, 2006 by Oleg Nesterov Committed by Linus Torvalds Sep 29, 2006

[PATCH] set EXIT_DEAD state in do_exit(), not in schedule()



schedule() checks PF_DEAD on every context switch and sets ->state = EXIT_DEAD
to ensure that the exiting task will be deactivated.  Note that this EXIT_DEAD
is in fact a "random" value, we can use any bit except normal TASK_XXX values.

It is better to set this state in do_exit() along with PF_DEAD flag and remove
that check in schedule().

We are safe wrt concurrent try_to_wake_up() (for example ptrace, tkill), it
can not change task's ->state: the 'state' argument of try_to_wake_up() can't
have EXIT_DEAD bit.  And in case when try_to_wake_up() sees a stale value of
->state == TASK_RUNNING it will do nothing.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent e8106b94

kernel/exit.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -957,6 +957,7 @@ fastcall NORET_TYPE void do_exit(long code)
		preempt_disable();
		BUG_ON(tsk->flags & PF_DEAD);
		tsk->flags \|= PF_DEAD;
		tsk->state = EXIT_DEAD;

		schedule();
		BUG();

kernel/sched.c

+0 −3

Original line number	Diff line number	Diff line
		@@ -3348,9 +3348,6 @@ need_resched_nonpreemptible:

		spin_lock_irq(&rq->lock);

		if (unlikely(prev->flags & PF_DEAD))
		prev->state = EXIT_DEAD;

		switch_count = &prev->nivcsw;
		if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
		switch_count = &prev->nvcsw;

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