ipmi: Fix a memory ordering issue

From a locking point of view it is safe to check waiting_msg without
a lock, but there is a memory ordering issue that causes it to
possibly not be set right when viewed from another processor.  We are
already claiming a lock right after that, move the check to inside
the lock to enforce the memory ordering.

Signed-off-by: Corey Minyard <cminyard@mvista.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
index 321ecb26df6a..f6646ed3047e 100644
--- a/drivers/char/ipmi/ipmi_si_intf.c
+++ b/drivers/char/ipmi/ipmi_si_intf.c
@@ -932,9 +932,6 @@ static void sender(void                *send_info,
         enum si_sm_result result;
         unsigned long     flags;
 
-        BUG_ON(smi_info->waiting_msg);
-        smi_info->waiting_msg = msg;
-
         debug_timestamp("Enqueue");
 
         if (smi_info->run_to_completion) {
@@ -942,7 +939,7 @@ static void sender(void                *send_info,
                  * If we are running to completion, start it and run
                  * transactions until everything is clear.
                  */
-                smi_info->curr_msg = smi_info->waiting_msg;
+                smi_info->curr_msg = msg;
                 smi_info->waiting_msg = NULL;
 
                 /*
@@ -960,6 +957,15 @@ static void sender(void                *send_info,
         }
 
         spin_lock_irqsave(&smi_info->si_lock, flags);
+        /*
+         * The following two lines don't need to be under the lock for
+         * the lock's sake, but they do need SMP memory barriers to
+         * avoid getting things out of order.  We are already claiming
+         * the lock, anyway, so just do it under the lock to avoid the
+         * ordering problem.
+         */
+        BUG_ON(smi_info->waiting_msg);
+        smi_info->waiting_msg = msg;
         check_start_timer_thread(smi_info);
         spin_unlock_irqrestore(&smi_info->si_lock, flags);
 }