Re: [PATCH] scsi: gdth: Only call dma_free_coherent when buf is not NULL in ioc_general

Nathan Chancellor
2019-03-08T21:31:43Z

On Fri, Mar 08, 2019 at 01:14:25PM -0800, Nick Desaulniers wrote:
> On Thu, Mar 7, 2019 at 3:19 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > When building with -Wsometimes-uninitialized, Clang warns:
> >
> > drivers/scsi/gdth.c:3662:6: warning: variable 'paddr' is used
> > uninitialized whenever 'if' condition is false
> > [-Wsometimes-uninitialized]
> >
> > Don't attempt to call dma_free_coherent when buf is NULL (meaning that
> > we never called dma_alloc_coherent and initialized paddr), which avoids
> > this warning.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/402
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> > drivers/scsi/gdth.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/scsi/gdth.c b/drivers/scsi/gdth.c
> > index e7f1dd4f3b66..0ca9b4393770 100644
> > --- a/drivers/scsi/gdth.c
> > +++ b/drivers/scsi/gdth.c
> > @@ -3697,8 +3697,9 @@ static int ioc_general(void __user *arg, char *cmnd)
> >
> > rval = 0;
> > out_free_buf:
> > - dma_free_coherent(&ha->pdev->dev, gen.data_len + gen.sense_len, buf,
> > - paddr);
> > + if (buf)
> > + dma_free_coherent(&ha->pdev->dev, gen.data_len + gen.sense_len,
> > + buf, paddr);
> > return rval;
> > }
> >
> > --
> > 2.21.0
> >
>
> Alternatively, paddr is a dma_addr_t defined in include/linux/types.h:
>
> #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
> typedef u64 dma_addr_t;
> #else
> typedef u32 dma_addr_t;
> #endif
>
> Just initializing it to zero might be simpler than complicating the
> control flow of this function further. Thoughts?
>
> diff --git a/drivers/scsi/gdth.c b/drivers/scsi/gdth.c
> index e7f1dd4f3b66..5a3f849ebf64 100644
> --- a/drivers/scsi/gdth.c
> +++ b/drivers/scsi/gdth.c
> @@ -3643,7 +3643,7 @@ static int ioc_general(void __user *arg, char *cmnd)
> gdth_ioctl_general gen;
> gdth_ha_str *ha;
> char *buf = NULL;
> - dma_addr_t paddr;
> + dma_addr_t paddr = 0U;
> int rval;
>
> if (copy_from_user(&gen, arg, sizeof(gdth_ioctl_general)))
> --
> Thanks,
> ~Nick Desaulniers

I suppose it depends on if it's okay to call dma_free_coherent without
dma_alloc_coherent. I did a scan of the tree before sending this out
and pretty much all sites that have error handling check that the third
parameter is not NULL before calling it.

I should have added Christoph to this thread when I initially sent it
out since commit 9f475ebff8e4 ("scsi: gdth: refactor ioc_general")
introduced this. Done now.

Cheers,
Nathan