From: "tip-bot2 for Frederic Weisbecker" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>,
Frederic Weisbecker <frederic@kernel.org>,
stable@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: timers/urgent] posix-cpu-timers: Fix rearm racing against process tick
Date: Tue, 20 Jul 2021 10:55:22 -0000 [thread overview]
Message-ID: <162677852264.395.4295146742807519075.tip-bot2@tip-bot2> (raw)
The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: 1a3402d93c73bf6bb4df6d7c2aac35abfc3c50e2
Gitweb: https://git.kernel.org/tip/1a3402d93c73bf6bb4df6d7c2aac35abfc3c50e2
Author: Frederic Weisbecker <frederic@kernel.org>
AuthorDate: Thu, 03 Jun 2021 01:15:59 +02:00
Committer: Frederic Weisbecker <frederic@kernel.org>
CommitterDate: Thu, 15 Jul 2021 01:20:10 +02:00
posix-cpu-timers: Fix rearm racing against process tick
Since the process wide cputime counter is started locklessly from
posix_cpu_timer_rearm(), it can be concurrently stopped by operations
on other timers from the same thread group, such as in the following
unlucky scenario:
CPU 0 CPU 1
----- -----
timer_settime(TIMER B)
posix_cpu_timer_rearm(TIMER A)
cpu_clock_sample_group()
(pct->timers_active already true)
handle_posix_cpu_timers()
check_process_timers()
stop_process_timers()
pct->timers_active = false
arm_timer(TIMER A)
tick -> run_posix_cpu_timers()
// sees !pct->timers_active, ignore
// our TIMER A
Fix this with simply locking process wide cputime counting start and
timer arm in the same block.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Fixes: 60f2ceaa8111 ("posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group")
Cc: stable@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
---
kernel/time/posix-cpu-timers.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 29a5e54..517be7f 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -991,6 +991,11 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
if (!p)
goto out;
+ /* Protect timer list r/w in arm_timer() */
+ sighand = lock_task_sighand(p, &flags);
+ if (unlikely(sighand == NULL))
+ goto out;
+
/*
* Fetch the current sample and update the timer's expiry time.
*/
@@ -1001,11 +1006,6 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
bump_cpu_timer(timer, now);
- /* Protect timer list r/w in arm_timer() */
- sighand = lock_task_sighand(p, &flags);
- if (unlikely(sighand == NULL))
- goto out;
-
/*
* Now re-arm for the new expiry time.
*/
reply other threads:[~2021-07-20 11:02 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=162677852264.395.4295146742807519075.tip-bot2@tip-bot2 \
--to=tip-bot2@linutronix.de \
--cc=ebiederm@xmission.com \
--cc=frederic@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=stable@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).