[PATCH] powerpc: Add write barrier before enabling DTL flags

[Jeremy Kerr <jk@ozlabs.org>]

Currently, we don't enforce any ordering for updates to the lppaca
when enabling dtl logging, so we may end up enabling logging before the
index fields have been established.

This change adds a smp_wmb() before doing the actual enable.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

---
 arch/powerpc/platforms/pseries/dtl.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/dtl.c b/arch/powerpc/platforms/pseries/dtl.c
index dc9b0f8..fafcaa0 100644
--- a/arch/powerpc/platforms/pseries/dtl.c
+++ b/arch/powerpc/platforms/pseries/dtl.c
@@ -107,6 +107,10 @@ static int dtl_enable(struct dtl *dtl)
 	/* set our initial buffer indices */
 	dtl->last_idx = lppaca[dtl->cpu].dtl_idx = 0;
 
+	/* ensure that our updates to the lppaca fields have occurred before
+	 * we actually enable the logging */
+	smp_wmb();
+
 	/* enable event logging */
 	lppaca[dtl->cpu].dtl_enable_mask = dtl_event_mask;