[PATCH 1/4] locking/rwsem: Avoid stale ->count for rwsem_down_write_failed()

[Davidlohr Bueso]

The field is obviously updated w.o the lock and needs a READ_ONCE
while waiting for lock holder(s) to go away, just like we do with
all other ->count accesses.

Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
---
 kernel/locking/rwsem-xadd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index df4dcb883b50..7d62772600cf 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -494,7 +494,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, 
int state)
                        }
                        schedule();
                        set_current_state(state);
-               } while ((count = sem->count) & RWSEM_ACTIVE_MASK);
+               } while ((count = READ_ONCE(sem->count)) & RWSEM_ACTIVE_MASK);
 
                raw_spin_lock_irq(&sem->wait_lock);
        }
-- 
2.8.1