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From: <benh@kernel.crashing.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: <torvalds@transmeta.com>, <linux-kernel@vger.kernel.org>,
        Hubertus Franke <frankeh@watson.ibm.com>
Subject: Re: [PATCH] Fast Userspace Mutexes. 
Date: Fri, 1 Mar 2002 01:46:19 +0100
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There seem to be a problem with PPC, you didn't put back the
PPC405_ERR77 macro in your new implementation. That means you
may hit a PPC 405gp CPU bugs and lose atomicity of lwarx/stwcx.

+#define __HAVE_ARCH_UPDATE_COUNT
+static inline int __update_count(atomic_t *count, int incr)
+{
+	int old_count, tmp;
+
+	__asm__ __volatile__("\n"
+"1:	lwarx	%0,0,%3\n"
+"	srawi	%1,%0,31\n"
+"	andc	%1,%0,%1\n"
+"	add	%1,%1,%4\n"
++	PPC405_ERR77(0,%3)
+"	stwcx.	%1,0,%3\n"
+"	bne	1b"
+	: "=&r" (old_count), "=&r" (tmp), "=m" (*count)
+	: "r" (count), "r" (incr), "m" (*count)
+	: "cc");

Ben.