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sched/cache: Fix stale preferred_llc for a new task

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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: 47d8696b95 ("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
This commit is contained in:
Chen Yu 2026-05-13 13:39:27 -07:00 committed by Peter Zijlstra
parent a7660ce159
commit c99b8593b0
1 changed files with 5 additions and 0 deletions
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5
kernel/sched/fair.c
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@ -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 */