linux-kernel - RE: [PATCH 0/10] use safer test on the result of find_first_zero

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Message-ID: <alpine.DEB.2.10.1406041148590.2441@hadrien>
Date:	Wed, 4 Jun 2014 11:52:32 +0200 (CEST)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	David Laight <David.Laight@...LAB.COM>
cc:	'Julia Lawall' <julia.lawall@...6.fr>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-rdma <linux-rdma@...r.kernel.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ath10k@...ts.infradead.org" <ath10k@...ts.infradead.org>,
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	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	driverdevel <devel@...verdev.osuosl.org>,
	"iss_storagedev@...com" <iss_storagedev@...com>,
	scsi <linux-scsi@...r.kernel.org>,
	linux-s390 <linux-s390@...r.kernel.org>,
	"adi-buildroot-devel@...ts.sourceforge.net" 
	<adi-buildroot-devel@...ts.sourceforge.net>
Subject: RE: [PATCH 0/10] use safer test on the result of
 find_first_zero_bit



On Wed, 4 Jun 2014, David Laight wrote:

> From: Julia Lawall
> > On Wed, 4 Jun 2014, Geert Uytterhoeven wrote:
> >
> > > Hi Julia,
> > >
> > > On Wed, Jun 4, 2014 at 11:07 AM, Julia Lawall <Julia.Lawall@...6.fr> wrote:
> > > > Find_first_zero_bit considers BITS_PER_LONG bits at a time, and thus may
> > > > return a larger number than the maximum position argument if that position
> > > > is not a multiple of BITS_PER_LONG.
> > >
> > > Shouldn't this be fixed in find_first_zero_bit() instead?
> >
> > OK, I could do that as well.  Most of the callers currently test with >=.
> > Should they be left as is, or changed to use ==?
>
> Do we want to add an extra test to find_first_zero_bit() and effectively
> slow down all the calls - especially those where the length is a
> multiple of 8 (probably the most common).

Currently, most of the calls test with >=, and most of the others seem to
need to (either the size value did not look like a multiple of anything in
particular, or it was eg read from a device).

Note that it is BITS_PER_LONG, so it seems like it is typically 32 or 64,
not 8.

> Maybe the documented return code should be changed to allow for the
> existing behaviour.

Sorry, I'm not sure to understand what you suggest here.

thanks,
julia
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