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authorSalman Qazi <sqazi@google.com>2010-10-12 07:25:19 -0700
committerThomas Gleixner <tglx@linutronix.de>2010-10-14 13:29:59 +0200
commitf13d4f979c518119bba5439dd2364d76d31dcd3f (patch)
tree952be8d19f13a3f0942c67c1f0d400d8dab472ea /kernel/hrtimer.c
parent53eeb64e808971207350386121f4bab12fa2f45f (diff)
downloadlinux-f13d4f979c518119bba5439dd2364d76d31dcd3f.tar.gz
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
Diffstat (limited to 'kernel/hrtimer.c')
-rw-r--r--kernel/hrtimer.c13
1 files changed, 11 insertions, 2 deletions
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 1decafbb6b1..72206cf5c6c 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;
}