From 1fcfa946609b5e919a6b953a64be6853af5cdf05 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Tue, 14 Jan 2020 13:39:02 -0500 Subject: [PATCH] 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 Signed-off-by: Waiman Long --- kernel/locking/rwsem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 44e68761f432..1dd3d53f43c3 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -1227,7 +1227,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) * without sleeping. */ if ((wstate == WRITER_HANDOFF) && - (rwsem_spin_on_owner(sem, 0) == OWNER_NULL)) + rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL) goto trylock_again; /* Block until there are no active lockers. */ -- 2.18.1