linux-kernel - Re: [PATCH] [RESEND] aic7xxx: replace kmalloc/memset by kzalloc

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Message-ID: <5514A679.5030005@free-electrons.com>
Date:	Thu, 26 Mar 2015 17:38:17 -0700
From:	Michael Opdenacker <michael.opdenacker@...e-electrons.com>
To:	"Elliott, Robert (Server Storage)" <Elliott@...com>,
	Joe Perches <joe@...ches.com>
CC:	Hannes Reinecke <hare@...e.de>,
	"JBottomley@...allels.com" <JBottomley@...allels.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RESEND] aic7xxx: replace kmalloc/memset by kzalloc

On 03/24/2015 04:16 PM, Elliott, Robert (Server Storage) wrote:
>
> It was a reply to the original post on 2014-10-16, not the resend
> this month. 
>
> From http://permalink.gmane.org/gmane.linux.kernel/1808168:
>
> kcalloc is helpful when one of the values is a variable that 
> might cause the multiply to overflow during runtime.  Here, 
> two constants are being multiplied together, which can
> be done and checked by the compiler at compile time.  
>
> Since kcalloc and kmalloc_array are both static inline 
> functions:
> static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags)
> {
>         if (size != 0 && n > SIZE_MAX / size)
>                 return NULL;
>         return __kmalloc(n * size, flags);
> }
> static inline void *kcalloc(size_t n, size_t size, gfp_t flags)
> {
>         return kmalloc_array(n, size, flags | __GFP_ZERO);
> }
>
> a compiler that detects an overflow will probably just reduce
> that to an inlined "return NULL."
> 	
> BUILD_BUG_ON could be used to trigger a compile-time error,
> instead of building a kernel that returns a run-time error.

Ok, I hope we agree to get back to kzalloc() for which the compiler
won't miss size_t overflows.

Thanks for the reviews!

Michael.

-- 
Michael Opdenacker, CEO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
+33 484 258 098


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