linux-kernel - [PATCH -tip 2/2] x86: Issue at least one memory barrier in stop_machine_text

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Date:	Wed, 03 Mar 2010 16:27:04 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>
Cc:	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...e.hu>, Jason Baron <jbaron@...hat.com>
Subject: [PATCH -tip 2/2] x86: Issue at least one memory barrier in
	stop_machine_text_poke().

Fix stop_machine_text_poke() to issue smp_mb() before exiting waiting
loop. Also, use ACCESS_ONCE() to check a flag according to Mathieu's
comment.

Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Jason Baron <jbaron@...hat.com>
---

 arch/x86/kernel/alternative.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 635e4f4..3236a11 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -596,9 +596,9 @@ static int __kprobes stop_machine_text_poke(void *data)
 		smp_wmb();	/* Make sure other cpus see that this has run */
 		wrote_text = 1;
 	} else {
-		while (!wrote_text)
-			smp_rmb();
-		sync_core();
+		while (!ACCESS_ONCE(wrote_text))
+			cpu_relax();
+		smp_mb();	/* Load wrote_text before following execution */
 	}
 
 	flush_icache_range((unsigned long)tpp->addr,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com
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