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locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN 

The commit 91d2a812df ("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: 91d2a812df ("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
This commit is contained in:
Waiman Long 2020-01-15 10:43:36 -05:00 committed by Peter Zijlstra
parent 51bfb1d11d
commit 39e7234f00
1 changed files with 2 additions and 2 deletions
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4
kernel/locking/rwsem.c
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@ -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. */