To: "Pravin Nanaware" <p.nanaware@nihilent.com>
Cc: "John Hubbard" <john.hubbard@gmail.com>,
       "LKML" <linux-kernel@vger.kernel.org>
Subject: Re: Bitops source problem
References: <1145971D427D7F43B0DBDAE22221C4B502CCE22D@nipns00a210.FPS.NIHILENT.COM>
From: Roland Dreier <rdreier@cisco.com>
Date: Wed, 16 Jan 2008 22:44:35 -0800
In-Reply-To: <1145971D427D7F43B0DBDAE22221C4B502CCE22D@nipns00a210.FPS.NIHILENT.COM> (Pravin Nanaware's message of "Thu, 17 Jan 2008 12:08:19 +0530")
Message-ID: <adamyr5x86k.fsf@cisco.com>
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 > 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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