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

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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>
This commit is contained in:
Oleg Nesterov 2006-09-29 02:01:09 -07:00 committed by Linus Torvalds
parent e8106b941c
commit 29b8849216
2 changed files with 1 additions and 3 deletions
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1
kernel/exit.c
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@ -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();

3
kernel/sched.c
View file

@ -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;