linux-kernel - Re: [PATCH] selftests/iommu: prevent use of uninitialized variable

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Message-ID: <y7xzjzbquglgrmbufbbqksvshuaofod6alql6gqfbzhq6s33pk@dw4ma6kctr5s>
Date: Tue, 23 Sep 2025 23:38:13 +0200
From: Alessandro Zanni <alessandrozanni.dev@...il.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Alessandro Zanni <alessandro.zanni87@...il.com>, kevin.tian@...el.com, 
	shuah@...nel.org, iommu@...ts.linux.dev, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/iommu: prevent use of uninitialized variable

On Tue, Sep 23, 2025 at 02:28:22PM -0300, Jason Gunthorpe wrote:
> On Tue, Sep 23, 2025 at 05:01:06PM +0200, Alessandro Zanni wrote:
> > Fix to avoid the usage of the `res` variable uninitialized in the
> > following macro expansions.
> > 
> > It solves the following warning:
> > In function ‘iommufd_viommu_vdevice_alloc’,
> >   inlined from ‘wrapper_iommufd_viommu_vdevice_alloc’ at
> > iommufd.c:2889:1:
> > ../kselftest_harness.h:760:12: warning: ‘ret’ may be used uninitialized
> > [-Wmaybe-uninitialized]
> >   760 |   if (!(__exp _t __seen)) { \
> >       |      ^
> > ../kselftest_harness.h:513:9: note: in expansion of macro ‘__EXPECT’
> >   513 |   __EXPECT(expected, #expected, seen, #seen, ==, 1)
> >       |   ^~~~~~~~
> > iommufd_utils.h:1057:9: note: in expansion of macro ‘ASSERT_EQ’
> >  1057 |   ASSERT_EQ(0, _test_cmd_trigger_vevents(self->fd, dev_id,
> > nvevents))
> >       |   ^~~~~~~~~
> > iommufd.c:2924:17: note: in expansion of macro
> > ‘test_cmd_trigger_vevents’
> >  2924 |   test_cmd_trigger_vevents(dev_id, 3);
> >       |   ^~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > The issue can be reproduced, building the tests, with the command:
> > make -C tools/testing/selftests TARGETS=iommu
> > 
> > Signed-off-by: Alessandro Zanni <alessandro.zanni87@...il.com>
> > ---
> >  tools/testing/selftests/iommu/iommufd_utils.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> I think it should be like this?
> 
> @@ -1042,15 +1042,12 @@ static int _test_cmd_trigger_vevents(int fd, __u32 dev_id, __u32 nvevents)
>                         .dev_id = dev_id,
>                 },
>         };
> -       int ret;
>  
> -       while (nvevents--) {
> -               ret = ioctl(fd, _IOMMU_TEST_CMD(IOMMU_TEST_OP_TRIGGER_VEVENT),
> -                           &trigger_vevent_cmd);
> -               if (ret < 0)
> +       while (nvevents--)
> +               if (ioctl(fd, _IOMMU_TEST_CMD(IOMMU_TEST_OP_TRIGGER_VEVENT),
> +                         &trigger_vevent_cmd))
>                         return -1;
> -       }
> -       return ret;
> +       return 0;
>  }
> 
> And add a fixes line?
> 
> Jason

Thank you for the reply.
I'm not sure the right behavior the test should have:
- in the version you proposed, when ioctl() returns a positive
value the loop ends and the next tests are skipped.
- in the original version, if the function ioctl() returns a
positive value the loop continues with the following tests.

Which one is the desired behavior?

Thanks,
Alessandro