mutex_can_spin_on_owner() is broken in that it would allow the compiler
to load lock->owner twice, seeing a pointer first time and a MULL
pointer the second time.
Signed-off-by: Peter Zijlstra <pet...@infradead.org>
---
kernel/mutex.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/mutex.c b/kernel/mutex.c
index ff05f4b..7ff48c5 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -209,11 +209,13 @@ int mutex_spin_on_owner(struct mutex *lock, struct
task_struct *owner)
*/
static inline int mutex_can_spin_on_owner(struct mutex *lock)
{
+ struct task_struct *owner;
int retval = 1;
rcu_read_lock();
- if (lock->owner)
- retval = lock->owner->on_cpu;
+ owner = ACCESS_ONCE(lock->owner);
+ if (owner)
+ retval = owner->on_cpu;
rcu_read_unlock();
/*
* if lock->owner is not set, the mutex owner may have just acquired
--
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