Re: [PATCH] dma-buf: Don't use typeof in va_arg

[Christian König]

Am 10.06.22 um 09:52 schrieb Jiabing Wan:
> On 2022/6/10 15:24, Christian König wrote:
> > Am 10.06.22 um 09:20 schrieb Wan Jiabing:
> > > Fix following coccicheck warning:
> > > ./drivers/dma-buf/st-dma-fence-unwrap.c:75:39-45: ERROR: reference 
> > > preceded by free on line 70
> > >
> > > Use 'struct dma_fence *' instead of 'typeof(*fences)' to avoid this
> > > warning and also fix other 'typeof(*fences)' to make them consistent.
> >
> > Well that doesn't looks correct to me.
> >
> > *fence should be valid at this point, why does coccicheck things it 
> > is freed?
>
> *fence is valid. Coccicheck reports this because fence is freed.
> But use 'struct dma_fence *' can avoid this wrong report.

Well in this case that's just a clear NAK.

Using typeof(*var) is perfectly valid and preferred should the type 
change at some point.

As far as I can see your cocci script is somehow reporting a false warning.

Regards,
Christian.

> I also grep all code and find it's unusual to use 'typeof' in va_arg, 
> only two files.
>
> grep -R "va_arg("  . | grep 'typeof'
> ./drivers/dma-buf/st-dma-fence-unwrap.c:                fences[i] = 
> va_arg(valist, typeof(*fences));
> ./drivers/dma-buf/st-dma-fence-unwrap.c: dma_fence_put(va_arg(valist, 
> typeof(*fences)));
> ./lib/test_scanf.c:             typeof(*expect) got = *va_arg(ap, 
> typeof(expect));              \
>
> And other files all use declaration name directly.
> So I send this patch makes code clearer and fix the wrong warning by 
> the way.
>
> Thanks,
> Wan Jiabing
>
> > Regards,
> > Christian.
> >
> > > Fixes: 0c5064fa8d5a ("dma-buf: cleanup dma_fence_unwrap selftest v2")
> > > Signed-off-by: Wan Jiabing <wanjiabing@xxxxxxxx>
> > > ---
> > >   drivers/dma-buf/st-dma-fence-unwrap.c | 4 ++--
> > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c 
> > > b/drivers/dma-buf/st-dma-fence-unwrap.c
> > > index 4105d5ea8dde..1137a6d90b32 100644
> > > --- a/drivers/dma-buf/st-dma-fence-unwrap.c
> > > +++ b/drivers/dma-buf/st-dma-fence-unwrap.c
> > > @@ -56,7 +56,7 @@ static struct dma_fence *mock_array(unsigned int 
> > > num_fences, ...)
> > >         va_start(valist, num_fences);
> > >       for (i = 0; i < num_fences; ++i)
> > > -        fences[i] = va_arg(valist, typeof(*fences));
> > > +        fences[i] = va_arg(valist, struct dma_fence *);
> > >       va_end(valist);
> > >         array = dma_fence_array_create(num_fences, fences,
> > > @@ -72,7 +72,7 @@ static struct dma_fence *mock_array(unsigned int 
> > > num_fences, ...)
> > >   error_put:
> > >       va_start(valist, num_fences);
> > >       for (i = 0; i < num_fences; ++i)
> > > -        dma_fence_put(va_arg(valist, typeof(*fences)));
> > > +        dma_fence_put(va_arg(valist, struct dma_fence *));
> > >       va_end(valist);
> > >       return NULL;
> > >   }