Commit 39e7234f authored Jan 15, 2020 by Waiman Long Committed by Peter Zijlstra Jan 17, 2020

locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN



The commit 91d2a812 ("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: 91d2a812 ("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

parent 51bfb1d1

kernel/locking/rwsem.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1226,8 +1226,8 @@ wait:
		* 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. */

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