On Fri, Jul 19, 2019 at 01:36:00PM +0200, Arnd Bergmann wrote:
> When CONFIG_LOCKDEP is set, every use of DECLARE_WAIT_QUEUE_HEAD_ONSTACK()
> produces an bogus 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; })
> ^~~~
>
> A patch for clang has already been proposed and should soon be
> merged for clang-9, but for now all clang versions produce the
> warning in an otherwise (almost) clean allmodconfig build.
>
> Link: https://bugs.llvm.org/show_bug.cgi?id=31829
> Link: https://bugs.llvm.org/show_bug.cgi?id=42604
> Link: https://lore.kernel.org/lkml/20190703081119.209976-1-a...@arndb.de/
> Link: https://reviews.llvm.org/D64678
> Link:
> https://storage.kernelci.org/next/master/next-20190717/arm64/allmodconfig/clang-8/build-warnings.log
> Suggested-by: Nathan Chancellor <natechancel...@gmail.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> ---
> v2: given that kernelci is getting close to reporting a clean build for
> clang, I'm trying again with a less invasive approach after my
> first version was not too popular.
> ---
> include/linux/wait.h | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/wait.h b/include/linux/wait.h
> index ddb959641709..276499ae1a3e 100644
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -70,8 +70,17 @@ extern void __init_waitqueue_head(struct wait_queue_head
> *wq_head, const char *n
> #ifdef CONFIG_LOCKDEP
> # define __WAIT_QUEUE_HEAD_INIT_ONSTACK(name) \
> ({ init_waitqueue_head(&name); name; })
> -# define DECLARE_WAIT_QUEUE_HEAD_ONSTACK(name) \
> +# if defined(__clang__) && __clang_major__ <= 9
> +/* work around https://bugs.llvm.org/show_bug.cgi?id=42604 */
> +# define DECLARE_WAIT_QUEUE_HEAD_ONSTACK(name)
> \
> + _Pragma("clang diagnostic push")
> \
> + _Pragma("clang diagnostic ignored \"-Wuninitialized\"")
> \
> + struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
> \
> + _Pragma("clang diagnostic pop")
> +# else
> +# define DECLARE_WAIT_QUEUE_HEAD_ONSTACK(name) \
> struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
> +# endif
While this is indeed much better than before; do we really want to do
this? That is, since clang-9 release will not need this, we're basically
doing the above for pre-release compilers only.
