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

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Message-ID: <20250924124550.GH2547959@ziepe.ca>
Date: Wed, 24 Sep 2025 09:45:50 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Alessandro Zanni <alessandrozanni.dev@...il.com>
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 11:38:13PM +0200, Alessandro Zanni wrote:
> 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?

Sorry it should be !ioctl()

The ioctl will only return 0 or -errno

Jason