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authorMichel Lespinasse <walken@google.com>2010-05-12 11:38:45 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-12 18:23:34 -0700
commit91af70814105f4c05e6e11b51c3269907b71794b (patch)
tree3857e57d3bccc1638ce2dc0413249cc2f3469d34
parentcea0d767c29669bf89f86e4aee46ef462d2ebae8 (diff)
rwsem: Test for no active locks in __rwsem_do_wake undo code
If there are no active threasd using a semaphore, it is always correct to unqueue blocked threads. This seems to be what was intended in the undo code. What was done instead, was to look for a sem count of zero - this is an impossible situation, given that at least one thread is known to be queued on the semaphore. The code might be correct as written, but it's hard to reason about and it's not what was intended (otherwise the goto out would have been unconditional). Go for checking the active count - the alternative is not worth the headache. Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--lib/rwsem.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/lib/rwsem.c b/lib/rwsem.c
index 3e3365e5665e..ceba8e28807a 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -136,9 +136,10 @@ __rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
out:
return sem;
- /* undo the change to count, but check for a transition 1->0 */
+ /* undo the change to the active count, but check for a transition
+ * 1->0 */
undo:
- if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) != 0)
+ if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) & RWSEM_ACTIVE_MASK)
goto out;
goto try_again;
}