linux-kernel - [PATCH 5/5] posix-cpu-timers: Stop disabling timers on mt-exec

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Message-ID: <87o8tityzs.fsf@x220.int.ebiederm.org>
Date:   Fri, 28 Feb 2020 11:15:03 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 5/5] posix-cpu-timers: Stop disabling timers on mt-exec

The reasons Oleg added the extra posix_cpu_timers_exit_group are not
entirely clear from his commit message.  Today all that
posix_cpu_timers_exit_group does is stop timers that are tracking the
task from firing.  Every other operation on those timers is still
allowed.

The practical implication of this is posix_cpu_timer_del which could
not get the siglock after the thread group leader has exited (because
sighand == NULL) would be able to run successfully because the timer
was already dequeued.

With that locking issue fixed there is no point in disabling all
of the timers.  So remove Oleg's ``tempoary'' hack.

Fixes: e0a70217107e ("posix-cpu-timers: workaround to suppress the problems with mt exec")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/exit.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 502b4995b688..c7f32101c2c8 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -103,17 +103,8 @@ static void __exit_signal(struct task_struct *tsk)

 #ifdef CONFIG_POSIX_TIMERS
 	posix_cpu_timers_exit(tsk);
-	if (group_dead) {
+	if (group_dead)
 		posix_cpu_timers_exit_group(tsk);
-	} else {
-		/*
-		 * This can only happen if the caller is de_thread().
-		 * FIXME: this is the temporary hack, we should teach
-		 * posix-cpu-timers to handle this case correctly.
-		 */
-		if (unlikely(has_group_leader_pid(tsk)))
-			posix_cpu_timers_exit_group(tsk);
-	}
 #endif

 	if (group_dead) {
-- 
2.25.0