locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN

The commit 91d2a812dfb9 ("locking/rwsem: Make handoff writer
optimistically spin on owner") will allow a recently woken up waiting
writer to spin on the owner. Unfortunately, if the owner happens to be
RWSEM_OWNER_UNKNOWN, the code will incorrectly spin on it leading to a
kernel crash. This is fixed by passing the proper non-spinnable bits
to rwsem_spin_on_owner() so that RWSEM_OWNER_UNKNOWN will be treated
as a non-spinnable target.

Fixes: 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically spin on owner")
Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20200115154336.8679-1-longman@redhat.com

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 44e68761f43213144a61b0cd2b489cfd1b8358bd..0d9b6be9ecc886cdae8067f479a6cd915929fef6 100644 (file)
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1226,8 +1226,8 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
                 * In this case, we attempt to acquire the lock again
                 * without sleeping.
                 */
-               if ((wstate == WRITER_HANDOFF) &&
-                   (rwsem_spin_on_owner(sem, 0) == OWNER_NULL))
+               if (wstate == WRITER_HANDOFF &&
+                   rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
                        goto trylock_again;
 
                /* Block until there are no active lockers. */