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>

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index c41f13c15e8fcafad1b5f6ce34ac4a2e38b8c325..e0b877099470101050d4aa665d62f4611ab3f018 100644 (file)
--- 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,