2018-11-16 05:43:35

by Masahiro Yamada

Subject: [PATCH] slab: fix 'dubious: x & !y' warning from Sparse

Sparse reports:
./include/linux/slab.h:332:43: warning: dubious: x & !y

Signed-off-by: Masahiro Yamada <[email protected]>
---

include/linux/slab.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 918f374..d395c73 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -329,7 +329,7 @@ static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags)
* If an allocation is both __GFP_DMA and __GFP_RECLAIMABLE, return
* KMALLOC_DMA and effectively ignore __GFP_RECLAIMABLE
*/
- return type_dma + (is_reclaimable & !is_dma) * KMALLOC_RECLAIM;
+ return type_dma + (is_reclaimable && !is_dma) * KMALLOC_RECLAIM;
}

/*
--
2.7.4

2018-11-16 08:40:36

by Michal Hocko

Subject: Re: [PATCH] slab: fix 'dubious: x & !y' warning from Sparse

On Fri 16-11-18 14:40:29, Masahiro Yamada wrote:
> Sparse reports:
> ./include/linux/slab.h:332:43: warning: dubious: x & !y

JFYI this has been discussed here http://lkml.kernel.org/r/[email protected]

> Signed-off-by: Masahiro Yamada <[email protected]>
> ---
>
> include/linux/slab.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 918f374..d395c73 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -329,7 +329,7 @@ static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags)
> * If an allocation is both __GFP_DMA and __GFP_RECLAIMABLE, return
> * KMALLOC_DMA and effectively ignore __GFP_RECLAIMABLE
> */
> - return type_dma + (is_reclaimable & !is_dma) * KMALLOC_RECLAIM;
> + return type_dma + (is_reclaimable && !is_dma) * KMALLOC_RECLAIM;
> }
>
> /*
> --
> 2.7.4

--
Michal Hocko
SUSE Labs

2018-11-16 13:52:45

by Christoph Lameter (Ampere)

Subject: Re: [PATCH] slab: fix 'dubious: x & !y' warning from Sparse

On Fri, 16 Nov 2018, Masahiro Yamada wrote:

> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 918f374..d395c73 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -329,7 +329,7 @@ static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags)
> * If an allocation is both __GFP_DMA and __GFP_RECLAIMABLE, return
> * KMALLOC_DMA and effectively ignore __GFP_RECLAIMABLE
> */
> - return type_dma + (is_reclaimable & !is_dma) * KMALLOC_RECLAIM;
> + return type_dma + (is_reclaimable && !is_dma) * KMALLOC_RECLAIM;
> }

Ok then lets revert the initial patch whose point was to avoid a branch.
&& causes a branch again.

2018-11-16 17:07:40

by Michal Hocko

Subject: Re: [PATCH] slab: fix 'dubious: x & !y' warning from Sparse

On Fri 16-11-18 13:51:19, Cristopher Lameter wrote:
> On Fri, 16 Nov 2018, Masahiro Yamada wrote:
>
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 918f374..d395c73 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -329,7 +329,7 @@ static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags)
> > * If an allocation is both __GFP_DMA and __GFP_RECLAIMABLE, return
> > * KMALLOC_DMA and effectively ignore __GFP_RECLAIMABLE
> > */
> > - return type_dma + (is_reclaimable & !is_dma) * KMALLOC_RECLAIM;
> > + return type_dma + (is_reclaimable && !is_dma) * KMALLOC_RECLAIM;
> > }
>
> Ok then lets revert the initial patch whose point was to avoid a branch.
> && causes a branch again.

I believe Vlastimil managed to get rid of the branch http://lkml.kernel.org/r/[email protected]

--
Michal Hocko
SUSE Labs