path: root/kernel/time/hrtimer.c
diff options
authorJulien Grall <julien.grall@arm.com>2019-08-21 10:24:09 +0100
committerThomas Gleixner <tglx@linutronix.de>2019-08-21 16:10:01 +0200
commit68b2c8c1e421096f4b46ac2ac502d25ca067a2a6 (patch)
tree7a3ed006c78c419038c960ff614300115bd7aef6 /kernel/time/hrtimer.c
parenthrtimer: Protect lockless access to timer->base (diff)
hrtimer: Don't take expiry_lock when timer is currently migrated
migration_base is used as a placeholder when an hrtimer is migrated to a different CPU. In the case that hrtimer_cancel_wait_running() hits a timer which is currently migrated it would pointlessly acquire the expiry lock of the migration base, which is even not initialized. Surely it could be initialized, but there is absolutely no point in acquiring this lock because the timer is guaranteed not to run it's callback for which the caller waits to finish on that base. So it would just do the inc/lock/dec/unlock dance for nothing. As the base switch is short and non-preemptible, there is no issue when the wait function returns immediately. The timer base and base->cpu_base cannot be NULL in the code path which is invoking that, so just replace those checks with a check whether base is migration base. [ tglx: Updated from RT patch. Massaged changelog. Added comment. ] Signed-off-by: Julien Grall <julien.grall@arm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20190821092409.13225-4-julien.grall@arm.com
Diffstat (limited to 'kernel/time/hrtimer.c')
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index f48864e2ff8a..ebbd0fb3512b 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1217,7 +1217,11 @@ void hrtimer_cancel_wait_running(const struct hrtimer *timer)
/* Lockless read. Prevent the compiler from reloading it below */
struct hrtimer_clock_base *base = READ_ONCE(timer->base);
- if (!timer->is_soft || !base || !base->cpu_base) {
+ /*
+ * Just relax if the timer expires in hard interrupt context or if
+ * it is currently on the migration base.
+ */
+ if (!timer->is_soft || base == &migration_base)