Messages in this thread Patch in this message | | | Date | Wed, 15 Apr 2015 11:41:56 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 1/3] hrtimer: Fix race between hrtimer_start() and __run_hrtimer() |
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Because we drop cpu_base->lock around calling hrtimer::function, it is possible for hrtimer_start() to come in between and enqueue the timer.
If hrtimer::function then returns HRTIMER_RESTART we'll hit the BUG_ON because HRTIMER_STATE_ENQUEUED will be set.
Since the above is a perfectly valid scenario, remove the BUG_ON and make the enqueue_hrtimer() call conditional on the timer not being enqueued already.
NOTE: in that concurrent scenario its entirely common for both sites to want to modify the hrtimer, since hrtimers don't provide serialization themselves be sure to provide some such that the hrtimer::function and the hrtimer_start() caller don't both try and fudge the expiration state at the same time.
To that effect, add a WARN when someone tries to forward an already enqueued timer.
Fixes: 2d44ae4d7135 ("hrtimer: clean up cpu->base locking tricks") Cc: Ben Segall <bsegall@google.com> Cc: Roman Gushchin <klamm@yandex-team.ru> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/time/hrtimer.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -791,6 +791,9 @@ u64 hrtimer_forward(struct hrtimer *time if (delta.tv64 < 0) return 0; + if (WARN_ON(timer->state & HRTIMER_STATE_ENQUEUED)) + return 0; + if (interval.tv64 < hrtimer_resolution) interval.tv64 = hrtimer_resolution; @@ -1131,11 +1134,14 @@ static void __run_hrtimer(struct hrtimer * Note: We clear the CALLBACK bit after enqueue_hrtimer and * we do not reprogramm the event hardware. Happens either in * hrtimer_start_range_ns() or in hrtimer_interrupt() + * + * Note: Because we dropped the cpu_base->lock above, + * hrtimer_start_range_ns() can have popped in and enqueued the timer + * for us already. */ - if (restart != HRTIMER_NORESTART) { - BUG_ON(timer->state != HRTIMER_STATE_CALLBACK); + if (restart != HRTIMER_NORESTART && + !(timer->state & HRTIMER_STATE_ENQUEUED)) enqueue_hrtimer(timer, base); - } WARN_ON_ONCE(!(timer->state & HRTIMER_STATE_CALLBACK));
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