On Fri, Mar 22, 2019 at 03:35:00PM +0100, Arnd Bergmann wrote:
> clang has identified a code path in which it thinks a
> variable may be unused:
>
> drivers/md/bcache/alloc.c:333:4: error: variable 'bucket' is used uninitialized whenever 'if' condition is false
> [-Werror,-Wsometimes-uninitialized]
> fifo_pop(&ca->free_inc, bucket);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop'
> #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i))
> ^~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/md/bcache/util.h:189:6: note: expanded from macro 'fifo_pop_front'
> if (_r) { \
> ^~
> drivers/md/bcache/alloc.c:343:46: note: uninitialized use occurs here
> allocator_wait(ca, bch_allocator_push(ca, bucket));
> ^~~~~~
> drivers/md/bcache/alloc.c:287:7: note: expanded from macro 'allocator_wait'
> if (cond) \
> ^~~~
> drivers/md/bcache/alloc.c:333:4: note: remove the 'if' if its condition is always true
> fifo_pop(&ca->free_inc, bucket);
> ^
> drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop'
> #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i))
> ^
> drivers/md/bcache/util.h:189:2: note: expanded from macro 'fifo_pop_front'
> if (_r) { \
> ^
> drivers/md/bcache/alloc.c:331:15: note: initialize the variable 'bucket' to silence this warning
> long bucket;
> ^
>
> This cannot happen in practice because we only enter the loop
> if there is at least one element in the list.
>
> Slightly rearranging the code makes this clearer to both the
> reader and the compiler, which avoids the warning.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Yes, I like this much better than my patch, thanks!
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> ---
> drivers/md/bcache/alloc.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
> index 5002838ea476..f8986effcb50 100644
> --- a/drivers/md/bcache/alloc.c
> +++ b/drivers/md/bcache/alloc.c
> @@ -327,10 +327,11 @@ static int bch_allocator_thread(void *arg)
> * possibly issue discards to them, then we add the bucket to
> * the free list:
> */
> - while (!fifo_empty(&ca->free_inc)) {
> + while (1) {
> long bucket;
>
> - fifo_pop(&ca->free_inc, bucket);
> + if (!fifo_pop(&ca->free_inc, bucket))
> + break;
>
> if (ca->discard) {
> mutex_unlock(&ca->set->bucket_lock);
> --
> 2.20.0
>
