Re: [PATCH] slab.h: Avoid using & for logical and of booleans

From: Pavel Machek <pavel@ucw.cz>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, Vlastimil Babka <vbabka@suse.cz>,
	Mel Gorman <mgorman@techsingularity.net>,
	Christoph Lameter <cl@linux.com>, Roman Gushchin <guro@fb.com>
Subject: Re: [PATCH] slab.h: Avoid using & for logical and of booleans
Date: Mon, 19 Nov 2018 12:04:28 +0100	[thread overview]
Message-ID: <20181119110428.GE28607@amd> (raw)
In-Reply-To: <20181105204000.129023-1-bvanassche@acm.org>

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On Mon 2018-11-05 12:40:00, Bart Van Assche wrote:
> This patch suppresses the following sparse warning:
> 
> ./include/linux/slab.h:332:43: warning: dubious: x & !y
> 
> Fixes: 1291523f2c1d ("mm, slab/slub: introduce kmalloc-reclaimable caches")
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Roman Gushchin <guro@fb.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  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 918f374e7156..97d0599ddb7b 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;
>  }
>  

What is wrong with && ? If logical and is better done by multiply,
that's compiler job, and compiler should be fixed to do it...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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