sched/fair: Fix find_idlest_group() to handle CPU affinity

Because of CPU affinity, the local group can be skipped which breaks the assumption that statistics are always collected for local group. With uninitialized local_sgs, the comparison is meaningless and the behavior unpredictable. This can even end up to use local pointer which is to NULL in this case. If the local group has been skipped because of CPU affinity, we return the idlest group. Fixes: 57abff0 ("sched/fair: Rework find_idlest_group()") Reported-by: John Stultz <[email protected]> Signed-off-by: Vincent Guittot <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Reviewed-by: Valentin Schneider <[email protected]> Tested-by: John Stultz <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Link: https://lkml.kernel.org/r/[email protected]
soumdtt · Dec 17, 2019 · 7ed735c · 7ed735c
1 parent c346695
commit 7ed735c
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
@@ -8417,6 +8417,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
 	if (!idlest)
 		return NULL;
 
+	/* The local group has been skipped because of CPU affinity */
+	if (!local)
+		return idlest;
+
 	/*
 	 * If the local group is idler than the selected idlest group
 	 * don't try and push the task.