linux-kernel - [PATCH 1/3] posix-timers: don't switch to ->group_leader if ->it

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Date:	Sun, 3 Aug 2008 21:49:10 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mark McLoughlin <markmc@...hat.com>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Roland McGrath <roland@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] posix-timers: don't switch to ->group_leader if ->it_process dies

(textually depends on posix-timers-fix-posix_timer_event-vs-dequeue_signal-race.patch)

posix_timer_event() drops SIGEV_THREAD_ID and switches to ->group_leader if
send_sigqueue() fails.

This is not very useful and doesn't work reliably. send_sigqueue() can only
fail if ->it_process is dead. But it can die before it dequeues the SI_TIMER
signal, in that case the timer stops anyway.

Remove this code. I guess it was needed a long ago to ensure that the timer
is not destroyed when when its creator thread dies.

Q: perhaps it makes sense to change sys_timer_settime() to return an error
if ->it_process is dead?

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- 26-rc2/kernel/posix-timers.c~1_DONT_RESEND	2008-07-23 20:24:05.000000000 +0400
+++ 26-rc2/kernel/posix-timers.c	2008-08-03 20:25:41.000000000 +0400
@@ -298,6 +298,7 @@ void do_schedule_next_timer(struct sigin
 
 int posix_timer_event(struct k_itimer *timr, int si_private)
 {
+	int shared, ret;
 	/*
 	 * FIXME: if ->sigq is queued we can race with
 	 * dequeue_signal()->do_schedule_next_timer().
@@ -316,20 +317,10 @@ int posix_timer_event(struct k_itimer *t
 	timr->sigq->info.si_tid = timr->it_id;
 	timr->sigq->info.si_value = timr->it_sigev_value;
 
-	if (timr->it_sigev_notify & SIGEV_THREAD_ID) {
-		struct task_struct *leader;
-		int ret = send_sigqueue(timr->sigq, timr->it_process, 0);
-
-		if (likely(ret >= 0))
-			return ret;
-
-		timr->it_sigev_notify = SIGEV_SIGNAL;
-		leader = timr->it_process->group_leader;
-		put_task_struct(timr->it_process);
-		timr->it_process = leader;
-	}
-
-	return send_sigqueue(timr->sigq, timr->it_process, 1);
+	shared = !(timr->it_sigev_notify & SIGEV_THREAD_ID);
+	ret = send_sigqueue(timr->sigq, timr->it_process, shared);
+	/* If we failed to send the signal the timer stops. */
+	return ret > 0;
 }
 EXPORT_SYMBOL_GPL(posix_timer_event);
 

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