The following commit has been merged into the sched/core branch of tip:
Commit-ID: c99b8593b060931c5a0a4b701689f8d6a2c00dbf
Gitweb: https://git.kernel.org/tip/c99b8593b060931c5a0a4b701689f8d6a2c00dbf
Author: Chen Yu <yu.c.chen@intel.com>
AuthorDate: Wed, 13 May 2026 13:39:27 -07:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 18 May 2026 21:33:18 +02:00
sched/cache: Fix stale preferred_llc for a new task
On fork without CLONE_VM, the child gets a new mm,
the parent's preferred_llc value is stale for the
child.
Fix this by resetting the task's preferred_llc to -1.
This bug was reported by sashiko.
Fixes: 47d8696b95f7 ("sched/cache: Assign preferred LLC ID to processes")
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/0ec7309d0e24ede97656754d1505b7490403d966.1778703694.git.tim.c.chen@linux.intel.com
---
kernel/sched/fair.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c249cae..2614315 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1914,6 +1914,11 @@ void init_sched_mm(struct task_struct *p)
init_task_work(work, task_cache_work);
work->next = work;
+ /*
+ * Reset new task's preference to avoid
+ * polluting account_llc_enqueue().
+ */
+ p->preferred_llc = -1;
}
#else /* CONFIG_SCHED_CACHE */