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From: ebiederm@xmission.com (Eric W. Biederman)
To: <linux-kernel@vger.kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>, Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH 5/5] posix-cpu-timers: Stop disabling timers on mt-exec
Date: Fri, 28 Feb 2020 11:15:03 -0600
Message-ID: <87o8tityzs.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <87k146vdw3.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Fri, 28 Feb 2020 11:07:56 -0600")


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@xmission.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


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-28 17:07 [PATCH 0/5] posix-cpu-timers: Graceful handling of reaped processes Eric W. Biederman
2020-02-28 17:08 ` [PATCH 1/5] posix-cpu-timers: cpu_clock_sample_group no longer needs siglock Eric W. Biederman
2020-03-01 10:27   ` [tip: timers/core] posix-cpu-timers: cpu_clock_sample_group() " tip-bot2 for Eric W. Biederman
2020-02-28 17:09 ` [PATCH 2/5] posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group Eric W. Biederman
2020-03-01 10:27   ` [tip: timers/core] " tip-bot2 for Eric W. Biederman
2020-02-28 17:09 ` [PATCH 3/5] posix-cpu-timers: Pass the task into arm_timer Eric W. Biederman
2020-03-01 10:27   ` [tip: timers/core] posix-cpu-timers: Pass the task into arm_timer() tip-bot2 for Eric W. Biederman
2020-02-28 17:11 ` [PATCH 4/5] posix-cpu-timers: Store a reference to a pid not a task Eric W. Biederman
2020-03-01 10:27   ` [tip: timers/core] " tip-bot2 for Eric W. Biederman
2020-03-04  8:57   ` tip-bot2 for Eric W. Biederman
2020-02-28 17:15 ` Eric W. Biederman [this message]
2020-03-01 10:27   ` [tip: timers/core] posix-cpu-timers: Stop disabling timers on mt-exec tip-bot2 for Eric W. Biederman
2020-03-04  8:57   ` tip-bot2 for Eric W. Biederman

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