The following commit has been merged into the sched/core branch of tip:
Commit-ID: d6b9afab44e23d537fb85ecf50330baaf9ec82e9
Gitweb: https://git.kernel.org/tip/d6b9afab44e23d537fb85ecf50330baaf9ec82e9
Author: Chen Yu <yu.c.chen@intel.com>
AuthorDate: Wed, 13 May 2026 13:39:22 -07:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 18 May 2026 21:33:17 +02:00
sched/cache: Fix checking active load balance by only considering the CFS task
The currently running task cur may not be a CFS task, such as
an RT or Deadline task. For non-CFS tasks, the task_util(cur)
utilization average is not maintained, so this might pass a
stale or meaningless value to can_migrate_llc().
Check if the task is CFS before getting its task_util().
This bug was reported by sashiko.
Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/f9161133cf040d286dca11344a112c5ef2a5253d.1778703694.git.tim.c.chen@linux.intel.com
---
kernel/sched/fair.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 96c61ce..c249cae 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10509,7 +10509,8 @@ alb_break_llc(struct lb_env *env)
/*
* All tasks prefer to stay on their current CPU.
* Do not pull a task from its preferred CPU if:
- * 1. It is the only task running there(not too imbalance); OR
+ * 1. It is the only task running and does not exceed
+ * imbalance allowance; OR
* 2. Migrating it away from its preferred LLC would violate
* the cache-aware scheduling policy.
*/
@@ -10522,7 +10523,7 @@ alb_break_llc(struct lb_env *env)
return true;
cur = rcu_dereference_all(env->src_rq->curr);
- if (cur)
+ if (cur && cur->sched_class == &fair_sched_class)
util = task_util(cur);
if (can_migrate_llc(env->src_cpu, env->dst_cpu,