[Skiboot] [PATCH 1/4] ipmi: Fix potential infinite loop in sync_msg polling

[Nicholas Piggin]

Current gcc with -Os happens to generate code that re-loads the variable
in the loop, but that could change without notice, and with -O2 it does
infinite loop if sync_msg is !NULL, because it is not declared volatile
and there is no compiler barrier in the loop.

Add the usual cpu_relax() there to provide the compiler barrier.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 core/ipmi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/core/ipmi.c b/core/ipmi.c
index bbc1a7b6..59aa95fc 100644
--- a/core/ipmi.c
+++ b/core/ipmi.c
@@ -170,7 +170,8 @@ void ipmi_queue_msg_sync(struct ipmi_msg *msg)
 	}
 
 	lock(&sync_lock);
-	while (sync_msg);
+	while (sync_msg)
+		cpu_relax();
 	sync_msg = msg;
 	if (msg->backend->disable_retry && !opal_booting())
 		msg->backend->disable_retry(msg);
-- 
2.40.1