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| author | Salman Qazi <sqazi@google.com> | 2010-10-12 07:25:19 -0700 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2010-10-14 13:29:59 +0200 |
| commit | f13d4f979c518119bba5439dd2364d76d31dcd3f (patch) | |
| tree | 952be8d19f13a3f0942c67c1f0d400d8dab472ea | |
| parent | 53eeb64e808971207350386121f4bab12fa2f45f (diff) | |
| download | blackbird-op-linux-f13d4f979c518119bba5439dd2364d76d31dcd3f.tar.gz blackbird-op-linux-f13d4f979c518119bba5439dd2364d76d31dcd3f.zip | |
hrtimer: Preserve timer state in remove_hrtimer()
The race is described as follows:
CPU X CPU Y
remove_hrtimer
// state & QUEUED == 0
timer->state = CALLBACK
unlock timer base
timer->f(n) //very long
hrtimer_start
lock timer base
remove_hrtimer // no effect
hrtimer_enqueue
timer->state = CALLBACK |
QUEUED
unlock timer base
hrtimer_start
lock timer base
remove_hrtimer
mode = INACTIVE
// CALLBACK bit lost!
switch_hrtimer_base
CALLBACK bit not set:
timer->base
changes to a
different CPU.
lock this CPU's timer base
The bug was introduced with commit ca109491f (hrtimer: removing all ur
callback modes) in 2.6.29
[ tglx: Feed new state via local variable and add a comment. ]
Signed-off-by: Salman Qazi <sqazi@google.com>
Cc: akpm@linux-foundation.org
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20101012142351.8485.21823.stgit@dungbeetle.mtv.corp.google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
| -rw-r--r-- | kernel/hrtimer.c | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 1decafbb6b1a..72206cf5c6cf 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -931,6 +931,7 @@ static inline int remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base) { if (hrtimer_is_queued(timer)) { + unsigned long state; int reprogram; /* @@ -944,8 +945,13 @@ remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base) debug_deactivate(timer); timer_stats_hrtimer_clear_start_info(timer); reprogram = base->cpu_base == &__get_cpu_var(hrtimer_bases); - __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE, - reprogram); + /* + * We must preserve the CALLBACK state flag here, + * otherwise we could move the timer base in + * switch_hrtimer_base. + */ + state = timer->state & HRTIMER_STATE_CALLBACK; + __remove_hrtimer(timer, base, state, reprogram); return 1; } return 0; @@ -1231,6 +1237,9 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now) BUG_ON(timer->state != HRTIMER_STATE_CALLBACK); enqueue_hrtimer(timer, base); } + + WARN_ON_ONCE(!(timer->state & HRTIMER_STATE_CALLBACK)); + timer->state &= ~HRTIMER_STATE_CALLBACK; } |
