On Fri, Mar 22, 2019 at 3:36 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
>
> clang fails to see that rbd_assert(0) ends in an unreachable code
> path and warns about a subsequent use of an uninitialized variable
> when CONFIG_PROFILE_ANNOTATED_BRANCHES is set:
>
> drivers/block/rbd.c:2402:4: error: variable 'ret' is used uninitialized whenever 'if' condition is false
> [-Werror,-Wsometimes-uninitialized]
> rbd_assert(0);
> ^~~~~~~~~~~~~
> drivers/block/rbd.c:563:7: note: expanded from macro 'rbd_assert'
> if (unlikely(!(expr))) { \
> ^~~~~~~~~~~~~~~~~
> include/linux/compiler.h:48:23: note: expanded from macro 'unlikely'
> # define unlikely(x) (__branch_check__(x, 0, __builtin_constant_p(x)))
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/block/rbd.c:2410:6: note: uninitialized use occurs here
> if (ret) {
> ^~~
> drivers/block/rbd.c:2402:4: note: remove the 'if' if its condition is always true
> rbd_assert(0);
> ^
> drivers/block/rbd.c:563:3: note: expanded from macro 'rbd_assert'
> if (unlikely(!(expr))) { \
> ^
> drivers/block/rbd.c:2376:9: note: initialize the variable 'ret' to silence this warning
> int ret;
> ^
> = 0
> 1 error generated.
>
> This seems to be a bug in clang, but is easy to work around by using
> an unconditional BUG().
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> drivers/block/rbd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 4ba967d65cf9..cbcc3baf3807 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -2399,7 +2399,7 @@ static int rbd_obj_read_from_parent(struct rbd_obj_request *obj_req)
> &obj_req->bvec_pos);
> break;
> default:
> - rbd_assert(0);
> + BUG();
> }
> } else {
> ret = rbd_img_fill_from_bvecs(child_img_req,
Hi Arnd,
You did a couple of these last year in commit c6244b3b2377 ("rbd: avoid
Wreturn-type warnings"). Let's change all of those default cases to BUG
in one go. Do you want to do that or should I?
Thanks,
Ilya
