6.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Breno Leitao <leitao@debian.org>
commit 25f52e81216884a7444bf07a606691feb09a94e3 upstream.
I am seeing some rcu_tasks stalls in the Meta fleet during reclaim.
INFO: rcu_tasks detected stalls on tasks:
0000000088620d09: .. nvcsw: 6735/6735 holdout: 1 idle_cpu: -1/8
task:GlobalCPUThread state:R running task pid:2552016 tgid:2524552
Call Trace:
shrink_lruvec
mem_cgroup_iter
shrink_node
do_try_to_free_pages
try_to_free_pages
__alloc_frozen_pages_noprof
alloc_pages_noprof
pte_alloc_one
__pte_alloc
handle_mm_fault
Nothing promises direct reclaim returns in bounded time, and the scan loop
in shrink_lruvec() only calls cond_resched(), which is a no-op on
PREEMPTION kernels. Involuntary preemption is not a Tasks-RCU quiescent
state, so the reclaiming task never reports one and becomes a holdout.
Upgrade it to cond_resched_tasks_rcu_qs(), which reports a quiescent state
even when cond_resched() does nothing.
PS: This has been discussed in [1]
Link: https://lore.kernel.org/20260810-rcu_task_shrink_lruvec-v1-1-4d9f7d5251cb@debian.org (local)
Link: https://lore.kernel.org/all/amdWVTs0WKOxguxP@gmail.com/ (local) [1]
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5864,7 +5864,7 @@ static void shrink_lruvec(struct lruvec
}
}
- cond_resched();
+ cond_resched_tasks_rcu_qs();
if (nr_reclaimed < nr_to_reclaim || proportional_reclaim)
continue;