[PATCH] bcache: Zero initialize bucket in bch_allocator_thread

[PATCH] bcache: Zero initialize bucket in bch_allocator_thread

[Nathan Chancellor]

When building with -Wsometimes-uninitialized, Clang warns:

drivers/md/bcache/alloc.c:333:4: warning: variable 'bucket' is used
uninitialized whenever 'if' condition is false
[-Wsometimes-uninitialized]

fifo_pop expands to a conditional depending on '!fifo_empty(...)', which
is the same condition as the while loop. It seems Clang can't piece
together that this condition will never been false as long as we are in
the while loop because they are the same condition. It's easy enough to
silence this warning by just explicitly zero initializing bucket.

Link: https://github.com/ClangBuiltLinux/linux/issues/396
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 drivers/md/bcache/alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
index 5002838ea476..c72094901ac6 100644
--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -328,7 +328,7 @@ static int bch_allocator_thread(void *arg)
 		 * the free list:
 		 */
 		while (!fifo_empty(&ca->free_inc)) {
-			long bucket;
+			long bucket = 0;
 
 			fifo_pop(&ca->free_inc, bucket);
 
-- 
2.21.0

Re: [PATCH] bcache: Zero initialize bucket in bch_allocator_thread

[Coly Li]

On 2019/3/8 6:10 上午, Nathan Chancellor wrote:
> When building with -Wsometimes-uninitialized, Clang warns:
> 
> drivers/md/bcache/alloc.c:333:4: warning: variable 'bucket' is used
> uninitialized whenever 'if' condition is false
> [-Wsometimes-uninitialized]
> 
> fifo_pop expands to a conditional depending on '!fifo_empty(...)', which
> is the same condition as the while loop. It seems Clang can't piece
> together that this condition will never been false as long as we are in
> the while loop because they are the same condition. It's easy enough to
> silence this warning by just explicitly zero initializing bucket.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/396
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

Hi Nathan,

Nice catch, I will add it to my for-test. Thanks.

Coly Li

> ---
>  drivers/md/bcache/alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
> index 5002838ea476..c72094901ac6 100644
> --- a/drivers/md/bcache/alloc.c
> +++ b/drivers/md/bcache/alloc.c
> @@ -328,7 +328,7 @@ static int bch_allocator_thread(void *arg)
>  		 * the free list:
>  		 */
>  		while (!fifo_empty(&ca->free_inc)) {
> -			long bucket;
> +			long bucket = 0;
>  
>  			fifo_pop(&ca->free_inc, bucket);
>  
> 


-- 

Coly Li

Re: [PATCH] bcache: Zero initialize bucket in bch_allocator_thread

[Arnd Bergmann]

On Fri, Mar 8, 2019 at 3:11 AM Coly Li <colyli@suse.de> wrote:
> On 2019/3/8 6:10 上午, Nathan Chancellor wrote:
> > When building with -Wsometimes-uninitialized, Clang warns:
> >
> > drivers/md/bcache/alloc.c:333:4: warning: variable 'bucket' is used
> > uninitialized whenever 'if' condition is false
> > [-Wsometimes-uninitialized]
> >
> > fifo_pop expands to a conditional depending on '!fifo_empty(...)', which
> > is the same condition as the while loop. It seems Clang can't piece
> > together that this condition will never been false as long as we are in
> > the while loop because they are the same condition. It's easy enough to
> > silence this warning by just explicitly zero initializing bucket.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/396
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
>
> Hi Nathan,
>
> Nice catch, I will add it to my for-test. Thanks.

I saw the same warning but came up with a nicer (IMHO) fix, see
https://lore.kernel.org/lkml/20190322143507.1256436-1-arnd@arndb.de/T/#u

        Arnd