From: Eric Dumazet edumazet@google.com
[ Upstream commit ff229eee3d897f52bd001c841f2d3cce8853ecdc ]
Followup to commit dd2261ed45aa ("hrtimer: Protect lockless access to timer->base")
lock_hrtimer_base() fetches timer->base without lock exclusion.
Compiler is allowed to read timer->base twice (even if considered dumb) which could end up trying to lock migration_base and return &migration_base.
base = timer->base; if (likely(base != &migration_base)) {
/* compiler reads timer->base again, and now (base == &migration_base)
raw_spin_lock_irqsave(&base->cpu_base->lock, *flags); if (likely(base == timer->base)) return base; /* == &migration_base ! */
Similarly the write sides must use WRITE_ONCE() to avoid store tearing.
Signed-off-by: Eric Dumazet edumazet@google.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lkml.kernel.org/r/20191008173204.180879-1-edumazet@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/time/hrtimer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 5ee77f1a8a925..e809868578e0c 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -159,7 +159,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer, struct hrtimer_clock_base *base;
for (;;) { - base = timer->base; + base = READ_ONCE(timer->base); if (likely(base != &migration_base)) { raw_spin_lock_irqsave(&base->cpu_base->lock, *flags); if (likely(base == timer->base)) @@ -239,7 +239,7 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base, return base;
/* See the comment in lock_hrtimer_base() */ - timer->base = &migration_base; + WRITE_ONCE(timer->base, &migration_base); raw_spin_unlock(&base->cpu_base->lock); raw_spin_lock(&new_base->cpu_base->lock);
@@ -248,10 +248,10 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base, raw_spin_unlock(&new_base->cpu_base->lock); raw_spin_lock(&base->cpu_base->lock); new_cpu_base = this_cpu_base; - timer->base = base; + WRITE_ONCE(timer->base, base); goto again; } - timer->base = new_base; + WRITE_ONCE(timer->base, new_base); } else { if (new_cpu_base != this_cpu_base && hrtimer_check_target(timer, new_base)) {