linux-kernel - Re: select(0, ..) is valid ?

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Message-ID: <Pine.LNX.4.64.0705151109021.31972@schroedinger.engr.sgi.com>
Date:	Tue, 15 May 2007 11:10:22 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Badari Pulavarty <pbadari@...ibm.com>, netdev@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: select(0, ..) is valid ?

On Tue, 15 May 2007, Andrew Morton wrote:

> I _think_ we can just do
> 
> --- a/fs/compat.c~a
> +++ a/fs/compat.c
> @@ -1566,9 +1566,13 @@ int compat_core_sys_select(int n, compat
>  	 */
>  	ret = -ENOMEM;
>  	size = FDS_BYTES(n);
> -	bits = kmalloc(6 * size, GFP_KERNEL);
> -	if (!bits)
> -		goto out_nofds;
> +	if (likely(size)) {
> +		bits = kmalloc(6 * size, GFP_KERNEL);
> +		if (!bits)
> +			goto out_nofds;
> +	} else {
> +		bits = NULL;
> +	}
>  	fds.in      = (unsigned long *)  bits;
>  	fds.out     = (unsigned long *) (bits +   size);
>  	fds.ex      = (unsigned long *) (bits + 2*size);
> _
> 
> I mean, if that oopses then I'd be very interested in finding out why.
> 
> But I'm starting to suspect that it would be better to permit kmalloc(0) in
> slub.  It depends on how many more of these things need fixing.
> 
> otoh, a kmalloc(0) could be a sign of some buggy/inefficient/weird code, so
> there's some value in forcing us to go look at all the callsites.
 
Hmmm... We could have kmalloc(0) return a pointer to the zero page? That 
would catch any writers?
-
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