[PATCH] aio: revert lock_kiocb()

lock_kiocb() was introduced to serialize retrying and cancellation.  In the
process of doing so it tried to sleep waiting for KIF_LOCKED while holding
the ctx_lock spinlock.  Recent fixes have ensured that multiple concurrent
retries won't be attempted for a given iocb.  Cancel has other problems and
has no significant in-tree users that have been complaining about it.  So
for the immediate future we'll revert sleeping with the lock held and will
address proper cancellation and retry serialization in the future.

Signed-off-by: Zach Brown <zach.brown@oracle.com>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/aio.h

@@ -24,7 +24,12 @@ struct kioctx;
 #define KIOCB_SYNC_KEY		(~0U)
 
 /* ki_flags bits */
-#define KIF_LOCKED		0
+/*
+ * This may be used for cancel/retry serialization in the future, but
+ * for now it's unused and we probably don't want modules to even
+ * think they can use it.
+ */
+/* #define KIF_LOCKED		0 */
 #define KIF_KICKED		1
 #define KIF_CANCELLED		2