[PATCH] aio: don't ref kioctx after decref in put_ioctx

put_ioctx's refcount debugging was doing an atomic_read after dropping its
reference when it wasn't the last ref, leaving a tiny race for another freeing
thread to sneak into.  This shifts the debugging before the ops, uses BUG_ON,
and reformats the defines a little.  Sadly, moving to inlines increased the
code size but this change decreases the code size by a whole 9 bytes :)

Signed-off-by: Zach Brown <zach.brown@oracle.com>
Cc: 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

@@ -210,8 +210,15 @@ struct kioctx *lookup_ioctx(unsigned long ctx_id);
 int FASTCALL(io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 				  struct iocb *iocb));
 
-#define get_ioctx(kioctx)	do { if (unlikely(atomic_read(&(kioctx)->users) <= 0)) BUG(); atomic_inc(&(kioctx)->users); } while (0)
-#define put_ioctx(kioctx)	do { if (unlikely(atomic_dec_and_test(&(kioctx)->users))) __put_ioctx(kioctx); else if (unlikely(atomic_read(&(kioctx)->users) < 0)) BUG(); } while (0)
+#define get_ioctx(kioctx) do {						\
+	BUG_ON(unlikely(atomic_read(&(kioctx)->users) <= 0));		\
+	atomic_inc(&(kioctx)->users);					\
+} while (0)
+#define put_ioctx(kioctx) do {						\
+	BUG_ON(unlikely(atomic_read(&(kioctx)->users) <= 0));		\
+	if (unlikely(atomic_dec_and_test(&(kioctx)->users))) 		\
+		__put_ioctx(kioctx);					\
+} while (0)
 
 #define in_aio() !is_sync_wait(current->io_wait)
 /* may be used for debugging */