diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2016-10-24 11:41:56 +0200 |
|---|---|---|
| committer | Runmin Wang <runminw@codeaurora.org> | 2017-01-05 17:27:10 -0800 |
| commit | 8965291e3dc17b6f1ba9c336100569215ac4e07d (patch) | |
| tree | 8b00b7e319b41bf8197d80539a711a531c0f5f15 | |
| parent | 2116b44bd37e0245ac3442be3dd094397ce017c9 (diff) | |
timers: Plug locking race vs. timer migration
Linus noticed that lock_timer_base() lacks a READ_ONCE() for accessing the
timer flags. As a consequence the compiler is allowed to reload the flags
between the initial check for TIMER_MIGRATION and the following timer base
computation and the spin lock of the base.
While this has not been observed (yet), we need to make sure that it never
happens.
Change-Id: I577327e02ab77b6de951ac2aa936cb5d5a4f477a
Fixes: 0eeda71bc30d ("timer: Replace timer base by a cpu index")
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1610241711220.4983@nanos
Cc: stable@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Git-commit: b831275a3553c32091222ac619cfddd73a5553fb
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[runminw@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Runmin Wang <runminw@codeaurora.org>
| -rw-r--r-- | kernel/time/timer.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 5ebefc7cfa4f..7d0d2632400d 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -811,8 +811,15 @@ static struct tvec_base *lock_timer_base(struct timer_list *timer, __acquires(timer->base->lock) { for (;;) { - u32 tf = timer->flags; struct tvec_base *base; + u32 tf; + + /* + * We need to use READ_ONCE() here, otherwise the compiler + * might re-read @tf between the check for TIMER_MIGRATING + * and spin_lock(). + */ + tf = READ_ONCE(timer->flags); if (!(tf & TIMER_MIGRATING)) { base = get_timer_base(tf); |