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

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Message-ID: <CAMuHMdV2wP43Lxf-UtCum37HyMPSboRb6RLNTHzm_ZNOBeJR0g@mail.gmail.com>
Date:	Wed, 4 Jun 2014 13:07:34 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Julia Lawall <julia.lawall@...6.fr>
Cc:	David Laight <David.Laight@...lab.com>,
	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>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"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>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 0/10] use safer test on the result of find_first_zero_bit

Hi Julia,

On Wed, Jun 4, 2014 at 1:00 PM, Julia Lawall <julia.lawall@...6.fr> wrote:
> OK, thanks.  I was only looking at the C code.
>
> But the C code contains a loop that is followed by:
>
>         if (!size)
>                 return result;
>         tmp = *p;
>
> found_first:
>         tmp |= ~0UL << size;
>         if (tmp == ~0UL)        /* Are any bits zero? */
>                 return result + size;   /* Nope. */
>
> In the first return, it would seem that result == size.  Could the second
> one be changed to just return size?  It should not hurt performance.

"size" may have been changed between function entry and this line.
So you have to store it in a temporary.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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