Commit 5c01ba49 authored Sep 23, 2009 by Oleg Nesterov Committed by Linus Torvalds Sep 24, 2009

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>

parent b4fe5182

kernel/exit.c

+9 −6

Original line number	Diff line number	Diff line
		@@ -1111,13 +1111,16 @@ static struct pid task_pid_type(struct task_struct task, enum pid_type type)
		return pid;
		}

		static int eligible_child(struct wait_opts wo, struct task_struct p)
		static inline int eligible_pid(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;
		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 (!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)

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