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| author | Frederic Weisbecker <frederic@kernel.org> | 2021-06-03 01:15:59 +0200 |
|---|---|---|
| committer | Frederic Weisbecker <frederic@kernel.org> | 2021-07-15 01:20:10 +0200 |
| commit | 1a3402d93c73bf6bb4df6d7c2aac35abfc3c50e2 (patch) | |
| tree | ff4ae75a802a4ef3b30d296afcc14597e0225b8a /kernel/time | |
| parent | Linux 5.14-rc1 (diff) | |
| download | linux-1a3402d93c73bf6bb4df6d7c2aac35abfc3c50e2.tar.xz linux-1a3402d93c73bf6bb4df6d7c2aac35abfc3c50e2.zip | |
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>
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/posix-cpu-timers.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 29a5e54e6e10..517be7fd175e 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. */ |