[Skiboot] [PATCH] timer: Stop calling list_top() racily

[Benjamin Herrenschmidt]

This will trip the debug checks in debug builds under some circumstances
and is actually a rather bad idea as we might look at a timer that is
concurrently being removed and modified, and thus incorrectly assume
there is no work to do.

Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
---
 core/timer.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/core/timer.c b/core/timer.c
index 4b5925fe..b10a5646 100644
--- a/core/timer.c
+++ b/core/timer.c
@@ -223,7 +223,6 @@ static void __check_timers(uint64_t now)
 
 void check_timers(bool from_interrupt)
 {
-	struct timer *t;
 	uint64_t now = mftb();
 
 	/* This is the polling variant, the SLW interrupt path, when it
@@ -231,9 +230,11 @@ void check_timers(bool from_interrupt)
 	 * the pollers
 	 */
 
-	/* Lockless "peek", a bit racy but shouldn't be a problem */
-	t = list_top(&timer_list, struct timer, link);
-	if (list_empty_nocheck(&timer_poll_list) && (!t || t->target > now))
+	/* Lockless "peek", a bit racy but shouldn't be a problem as
+	 * we are only looking at whether the list is empty
+	 */
+	if (list_empty_nocheck(&timer_poll_list) &&
+	    list_empty_nocheck(&timer_list))
 		return;
 
 	/* Take lock and try again */