From: Andrew Morton <akpm@linux-foundation.org>
To: Breno Leitao <leitao@debian.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
paulmck@kernel.org, puranjay@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
kernel-team@meta.com
Subject: Re: [PATCH] mm/kmemleak: report RCU-tasks quiescent states during the scan
Date: Mon, 20 Jul 2026 15:39:17 -0700 [thread overview]
Message-ID: <20260720153917.2e428e489cd0873ac6d4e6da@linux-foundation.org> (raw)
In-Reply-To: <20260720-kmemleak_rcu_task-v1-1-5b460ade777d@debian.org>
On Mon, 20 Jul 2026 06:23:45 -0700 Breno Leitao <leitao@debian.org> wrote:
> kmemleak_scan() can run for ages on large debug kernels. It was
> causing some soft-lockups which I got fixed with commit
> 3175fcfec8b16baeb ("mm/kmemleak: avoid soft lockup when scanning task
> stacks") with our beloved cond_resched().
>
> I've got the fix above deployed in the Meta fleet, and now I am seeing:
>
> INFO: rcu_tasks detected stalls on tasks:
> task:kmemleak state:R ... nvcsw: 274/274 holdout: 1 idle_cpu: -1/3
> scan_block
> scan_gray_list
> kmemleak_scan
>
> and, worse, blocks the callers waiting on that grace period. Here a BPF
> struct_ops map free, which waits via synchronize_rcu_mult(call_rcu,
> call_rcu_tasks), is stuck long enough to also trip the hung task check:
>
> INFO: task kworker/...:bpf_map_free_deferred blocked for 122 seconds
> __wait_rcu_gp
> bpf_struct_ops_map_free
>
> Then I've learned that cond_resched() is not an RCU-tasks quiescent
> state, so, we need to use stronger primitives.
>
> Use cond_resched_tasks_rcu_qs() at the scan reschedule points so the scan
> reports an RCU-tasks quiescent state as it proceeds.
>
> Inspired by commit b96285e10aad ("tracing: Have osnoise_main() add a
> quiescent state for task rcu").
I'll add
Fixes: c4b28963fd79 ("mm/kmemleak: rely on rcu for task stack scanning")
Cc: <stable@vger.kernel.org>
.
.
next prev parent reply other threads:[~2026-07-20 22:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-20 13:23 [PATCH] mm/kmemleak: report RCU-tasks quiescent states during the scan Breno Leitao
2026-07-20 13:37 ` sashiko-bot
2026-07-20 15:25 ` Paul E. McKenney
2026-07-20 22:39 ` Andrew Morton [this message]
2026-07-21 4:21 ` Paul E. McKenney
2026-07-21 0:00 ` SJ Park
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