On Fri, Mar 22, 2019 at 03:30:08PM +0100, Arnd Bergmann wrote: > On Fri, Mar 8, 2019 at 10:14 PM 'Nick Desaulniers' via Clang Built > Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote: > > > > On Thu, Mar 7, 2019 at 3:19 PM Nathan Chancellor > > <natechancellor@xxxxxxxxx> 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@xxxxxxxxx> > > > --- > > > 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; > > > } > > I came up with a different fix for this, but I think yours is better > > Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx> > > For reference, this was my version: This is also what I had initially but I felt this was more future proof and matches how the rest of the tree handles calls to dma_free_coherent. Thanks for the review! Nathan > > diff --git a/drivers/scsi/gdth.c b/drivers/scsi/gdth.c > index e7f1dd4f3b66..c01f243902e1 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 (gen.data_len + gen.sense_len > 0) > + dma_free_coherent(&ha->pdev->dev, gen.data_len + > gen.sense_len, buf, > + paddr); > return rval; > } > > > > 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? > > No, blindly shutting up warnings is almost never the > right solution, even when they are false positives. The code > might change in the future and the bogus initialization would > then prevent the compiler from warning about a new bug. > > Arnd
