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do_wait-wakeup-optimization: fix child_wait_callback()->eligible_child() usage 

child_wait_callback()->eligible_child() is not right, we can miss the
wakeup if the task was detached before __wake_up_parent() and the caller
of do_wait() didn't use __WALL.

Move ->wo_pid checks from eligible_child() to the new helper,
eligible_pid(), and change child_wait_callback() to use it instead of
eligible_child().

Note: actually I think it would be better to fix the __WCLONE check in
eligible_child(), it doesn't look exactly right.  But it is not clear what
is the supposed behaviour, and any change is user-visible.

Reported-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@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 2009-09-23 15:56:48 -07:00 committed by Linus Torvalds
parent b4fe51823d
commit 5c01ba49e6
1 changed files with 9 additions and 6 deletions
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15
kernel/exit.c
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@ -1111,13 +1111,16 @@ static struct pid *task_pid_type(struct task_struct *task, enum pid_type type)
return pid;
}
static inline int eligible_pid(struct wait_opts *wo, struct task_struct *p)
{
return wo->wo_type == PIDTYPE_MAX ||
task_pid_type(p, wo->wo_type) == wo->wo_pid;
}
static int eligible_child(struct wait_opts *wo, struct task_struct *p)
{
if (wo->wo_type < PIDTYPE_MAX) {
if (task_pid_type(p, wo->wo_type) != wo->wo_pid)
return 0;
}
if (!eligible_pid(wo, p))
return 0;
/* Wait for all children (clone and not) if __WALL is set;
* otherwise, wait for clone children *only* if __WCLONE is
* set; otherwise, wait for non-clone children *only*. (Note:
@ -1578,7 +1581,7 @@ static int child_wait_callback(wait_queue_t *wait, unsigned mode,
child_wait);
struct task_struct *p = key;
if (!eligible_child(wo, p))
if (!eligible_pid(wo, p))
return 0;
if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)