linux-kernel - [tip: timers/core] posix-cpu-timers: Stop disabling timers on mt-exec

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Date:   Wed, 04 Mar 2020 08:57:23 -0000
From:   "tip-bot2 for Eric W. Biederman" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: timers/core] posix-cpu-timers: Stop disabling timers on mt-exec

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     b95e31c07c5eb4f5c0769f12b38b0343d7961040
Gitweb:        https://git.kernel.org/tip/b95e31c07c5eb4f5c0769f12b38b0343d7961040
Author:        Eric W. Biederman <ebiederm@...ssion.com>
AuthorDate:    Fri, 28 Feb 2020 11:15:03 -06:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 04 Mar 2020 09:54:55 +01:00

posix-cpu-timers: Stop disabling timers on mt-exec

The reasons why the extra posix_cpu_timers_exit_group() invocation has been
added are not entirely clear from the 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 this ``tempoary'' hack.

Fixes: e0a70217107e ("posix-cpu-timers: workaround to suppress the problems with mt exec")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/87o8tityzs.fsf@x220.int.ebiederm.org

---
 kernel/exit.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 2833ffb..df54631 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) {