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exit: avoid sig->count in de_thread/__exit_signal synchronization

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de_thread() and __exit_signal() use signal_struct->count/notify_count for
synchronization.  We can simplify the code and use ->notify_count only.
Instead of comparing these two counters, we can change de_thread() to set
->notify_count = nr_of_sub_threads, then change __exit_signal() to
dec-and-test this counter and notify group_exit_task.

Note that __exit_signal() checks "notify_count > 0" just for symmetry with
exit_notify(), we could just check it is != 0.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2010-05-26 14:43:11 -07:00 committed by Linus Torvalds
parent 09faef11df
commit d344193a05
2 changed files with 7 additions and 8 deletions
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13
fs/exec.c
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@ -768,7 +768,6 @@ static int de_thread(struct task_struct *tsk)
struct signal_struct *sig = tsk->signal;
struct sighand_struct *oldsighand = tsk->sighand;
spinlock_t *lock = &oldsighand->siglock;
int count;
if (thread_group_empty(tsk))
goto no_thread_group;
@ -785,13 +784,13 @@ static int de_thread(struct task_struct *tsk)
spin_unlock_irq(lock);
return -EAGAIN;
}
sig->group_exit_task = tsk;
zap_other_threads(tsk);
/* Account for the thread group leader hanging around: */
count = thread_group_leader(tsk) ? 1 : 2;
sig->notify_count = count;
while (atomic_read(&sig->count) > count) {
sig->group_exit_task = tsk;
sig->notify_count = zap_other_threads(tsk);
if (!thread_group_leader(tsk))
sig->notify_count--;
while (sig->notify_count) {
__set_current_state(TASK_UNINTERRUPTIBLE);
spin_unlock_irq(lock);
schedule();

2
kernel/exit.c
View File

@ -97,7 +97,7 @@ static void __exit_signal(struct task_struct *tsk)
* If there is any task waiting for the group exit
* then notify it:
*/
if (sig->group_exit_task && atomic_read(&sig->count) == sig->notify_count)
if (sig->notify_count > 0 && !--sig->notify_count)
wake_up_process(sig->group_exit_task);
if (tsk == sig->curr_target)