From: John Hubbard <john.hubbard@gmail.com>
To: Pravin Nanaware <p.nanaware@nihilent.com>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: Re: Bitops source problem
Date: Wed, 16 Jan 2008 21:47:16 -0800 [thread overview]
Message-ID: <478EEBE4.40400@gmail.com> (raw)
In-Reply-To: <1145971D427D7F43B0DBDAE22221C4B5035FDDAC@nipns00a210.FPS.NIHILENT.COM>
Pravin Nanaware wrote:
> Hi,
>
> I was just going through the include file in the /usr/include/asm/bitops.h
>
> The function description describes it as non-atomic but it seems it is not.
>
> static __inline__ void __change_bit(int nr, volatile void * addr)
> {
> __asm__ __volatile__(
> "btcl %1,%0"
> :"=m" (ADDR)
> :"Ir" (nr));
> }
>
> The kernel version I am using is 2.6.9-42. Is it right or am I missing something ?
>
> Thanks,
> Pravin
>
The bitops.h comments are correct: the btc IA-32 instruction is only
atomic if used with the lock prefix. The function above does not use the
lock prefix, so it is not atomic.
thanks,
John Hubbard
next prev parent reply other threads:[~2008-01-17 5:47 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-17 5:09 Bitops source problem Pravin Nanaware
2008-01-17 5:47 ` John Hubbard [this message]
-- strict thread matches above, loose matches on Subject: below --
2008-01-17 6:38 Pravin Nanaware
2008-01-17 6:44 ` Roland Dreier
2008-01-17 6:59 ` KOSAKI Motohiro
2008-01-17 8:11 Pravin Nanaware
2008-01-17 19:32 ` Roland Dreier
2008-01-18 4:40 Pravin Nanaware
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