linux-kernel - RE: Bitops source problem

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Message-ID: <1145971D427D7F43B0DBDAE22221C4B5035FDDAD@nipns00a210.FPS.NIHILENT.COM>
Date:	Thu, 17 Jan 2008 13:41:20 +0530
From:	"Pravin Nanaware" <p.nanaware@...ilent.com>
To:	"Roland Dreier" <rdreier@...co.com>
Cc:	"John Hubbard" <john.hubbard@...il.com>,
	"LKML" <linux-kernel@...r.kernel.org>
Subject: RE: Bitops source problem

Yes, indeed none of the atomic bit operations functions has LOCK_PREFIX in my version of Linux kernel.

Regards,
Pravin


-----Original Message-----
From: linux-kernel-owner@...r.kernel.org
[mailto:linux-kernel-owner@...r.kernel.org]On Behalf Of Roland Dreier
Sent: Thursday, January 17, 2008 12:15 PM
To: Pravin Nanaware
Cc: John Hubbard; LKML
Subject: Re: Bitops source problem


 > Then, I think there is a problem with the function written below which is meant to be atomic.
 > 
 > static __inline__ void change_bit(int nr, volatile void * addr)
 > {
 >         __asm__ __volatile__(
 >                 "btcl %1,%0"
 >                 :"=m" (ADDR)
 >                 :"Ir" (nr));
 > }

If that is indeed the source of your change_bit function then there is
a problem.  However in my kernel tree there is a LOCK_PREFIX in the
definition of the atomic version.  I don't have your exact source tree
handy, but on a local RHEL4 system, the LOCK_PREFIX is still there:

static inline void change_bit(int nr, volatile unsigned long * addr)
{
        __asm__ __volatile__( LOCK_PREFIX
                "btcl %1,%0"
                :"=m" (ADDR)
                :"Ir" (nr));
}

 - R.
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