Linus,
please pull the latest timers-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
timers-urgent-for-linus
A single fix for a long standing race versus timers scheduled on a
target cpu which got exposed by recent changes in the workqueue
implementation.
Thanks,
tglx
------------------>
Tejun Heo (1):
timers: Use proper base migration in add_timer_on()
kernel/time/timer.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 74591ba9474f..bbc5d1114583 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -977,13 +977,29 @@ EXPORT_SYMBOL(add_timer);
*/
void add_timer_on(struct timer_list *timer, int cpu)
{
- struct tvec_base *base = per_cpu_ptr(&tvec_bases, cpu);
+ struct tvec_base *new_base = per_cpu_ptr(&tvec_bases, cpu);
+ struct tvec_base *base;
unsigned long flags;
timer_stats_timer_set_start_info(timer);
BUG_ON(timer_pending(timer) || !timer->function);
- spin_lock_irqsave(&base->lock, flags);
- timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
+
+ /*
+ * If @timer was on a different CPU, it should be migrated with the
+ * old base locked to prevent other operations proceeding with the
+ * wrong base locked. See lock_timer_base().
+ */
+ base = lock_timer_base(timer, &flags);
+ if (base != new_base) {
+ timer->flags |= TIMER_MIGRATING;
+
+ spin_unlock(&base->lock);
+ base = new_base;
+ spin_lock(&base->lock);
+ WRITE_ONCE(timer->flags,
+ (timer->flags & ~TIMER_BASEMASK) | cpu);
+ }
+
debug_activate(timer, timer->expires);
internal_add_timer(base, timer);
spin_unlock_irqrestore(&base->lock, flags);
--
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