[PATCH] rbd: avoid clang -Wuninitialized warning

[PATCH] rbd: avoid clang -Wuninitialized warning

[Arnd Bergmann]

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@arndb.de>
---
 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,
-- 
2.20.0

Re: [PATCH] rbd: avoid clang -Wuninitialized warning

[Ilya Dryomov]

On Fri, Mar 22, 2019 at 3:36 PM Arnd Bergmann <arnd@arndb.de> 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@arndb.de>
> ---
>  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

Re: [PATCH] rbd: avoid clang -Wuninitialized warning

[Arnd Bergmann]

On Fri, Mar 22, 2019 at 5:33 PM Ilya Dryomov <idryomov@gmail.com> wrote:
>
> On Fri, Mar 22, 2019 at 3:36 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > 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").

Ah, I had completely forgotten about that. Different bug and different
compiler, but same solution ;-)

>  Let's change all of those default cases to BUG
> in one go.  Do you want to do that or should I?

I've prepared another patch now and sent it out, please
apply it on top. I'd like this one-line patch to stay separate though
since it captures the warning message and may need to
be backported to stable kernels later.

      Arnd

Re: [PATCH] rbd: avoid clang -Wuninitialized warning

[Ilya Dryomov]

On Fri, Mar 22, 2019 at 5:55 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Mar 22, 2019 at 5:33 PM Ilya Dryomov <idryomov@gmail.com> wrote:
> >
> > On Fri, Mar 22, 2019 at 3:36 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > >
> > > 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").
>
> Ah, I had completely forgotten about that. Different bug and different
> compiler, but same solution ;-)
>
> >  Let's change all of those default cases to BUG
> > in one go.  Do you want to do that or should I?
>
> I've prepared another patch now and sent it out, please
> apply it on top. I'd like this one-line patch to stay separate though
> since it captures the warning message and may need to
> be backported to stable kernels later.

Applied.

Thanks,

                Ilya