When CONFIG_LOCKDEP is set, every use of DECLARE_WAIT_QUEUE_HEAD_ONSTACK()
produces an annoying warning from clang, which is particularly annoying
for allmodconfig builds:
fs/namei.c:1646:34: error: variable 'wq' is uninitialized when used within its
own initialization [-Werror,-Wuninitialized]
DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
^~
include/linux/wait.h:74:63: note: expanded from macro
'DECLARE_WAIT_QUEUE_HEAD_ONSTACK'
struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
~~~~ ^~~~
include/linux/wait.h:72:33: note: expanded from macro
'__WAIT_QUEUE_HEAD_INIT_ONSTACK'
({ init_waitqueue_head(&name); name; })
^~~~
After playing with it for a while, I have found a way to rephrase the
macro in a way that should work well with both gcc and clang and not
produce this warning. The open-coded __WAIT_QUEUE_HEAD_INIT_ONSTACK
is a little more verbose than the original version by Peter Zijlstra,
but avoids the gcc-ism that suppresses warnings when assigning a
variable to itself.
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Arnd Bergmann <a...@arndb.de>
---
include/linux/wait.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/include/linux/wait.h b/include/linux/wait.h
index ddb959641709..84e39643b780 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -68,8 +68,15 @@ extern void __init_waitqueue_head(struct wait_queue_head
*wq_head, const char *n
} while (0)
#ifdef CONFIG_LOCKDEP
-# define __WAIT_QUEUE_HEAD_INIT_ONSTACK(name) \
- ({ init_waitqueue_head(&name); name; })
+# define __WAIT_QUEUE_HEAD_INIT_ONSTACK(name) {
\
+ .lock = __SPIN_LOCK_UNLOCKED(name.lock),
\
+ .head = ({
\
+ static struct lock_class_key __key;
\
+ lockdep_set_class_and_name(&(name).lock, &__key, # name);
\
+ (struct list_head){ &(name).head, &(name).head };
\
+ }),
\
+}
+
# define DECLARE_WAIT_QUEUE_HEAD_ONSTACK(name) \
struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
#else
--
2.20.0
