[tip:perf/pebs] x86: Issue at least one memory barrier in stop_machine_text_poke()

[tip-bot for Masami Hiramatsu <mhiramat@redhat.com>]

Commit-ID:  e5a11016643d1ab7172193591506d33a844734cc
Gitweb:     http://git.kernel.org/tip/e5a11016643d1ab7172193591506d33a844734cc
Author:     Masami Hiramatsu <mhiramat@redhat.com>
AuthorDate: Wed, 3 Mar 2010 22:38:50 -0500
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 4 Mar 2010 11:39:21 +0100

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, and use cpu_relax() for waiting.

Changes in v2:
 - Don't use ACCESS_ONCE().

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
Cc: Jason Baron <jbaron@redhat.com>
LKML-Reference: <20100304033850.3819.74590.stgit@localhost6.localdomain6>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/alternative.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index c41f13c..e0b8770 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -595,8 +595,8 @@ static int __kprobes stop_machine_text_poke(void *data)
 		wrote_text = 1;
 	} else {
 		while (!wrote_text)
-			smp_rmb();
-		sync_core();
+			cpu_relax();
+		smp_mb();	/* Load wrote_text before following execution */
 	}
 
 	flush_icache_range((unsigned long)tpp->addr,