From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D95CF3AC0ED; Sat, 12 Sep 2026 17:02:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789232550; cv=none; b=nTyR7irsICmgoJvum3U7CuUFqNTEdAbLvIEopIBU9s9QmW6bYOHtVCQ4G/eLV/lIrCSMh3QhISNGvk65mB2FVYrpTHlTuMKub+61vMfgp3ccF1WfX9lM5y4cK4FW40+tLYVXnd8Q+Q1ZUHejSTL2yNpzyQvtYRZuSl2Tz3e1jF0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789232550; c=relaxed/simple; bh=SbXAKL4F6pd7ZD3bYYe3o0NU07maj3i5UssxMxsqTQA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GyiS2xrIj2yjI/2G9y+Ym/nWGHpxegsZ6qDcDQQeWCwrI9V0716yZIIkfyDRWCF9mlIViL1332gwu7yjLti8D59rInERPTP+Rlt5AqLsw8u5LGayZ19VSm8GhuDAJureNXDfNb56Z1TJOusilogdrpb6C6tXb5ZFjBwzt8q+99w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=h933jAcc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="h933jAcc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF5911F000FF; Sat, 12 Sep 2026 17:02:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789232548; bh=zTxEAqEuX89klez98Zz5hzOmAP8ir5DnKilrUSB742I=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=h933jAcc8y1Ap4NPWPTp89bsFXSbX8A++xxdGYzodKf5cej1JzCI47mFf4wOSjUGZ sEZCboAz0jQaijrWwnqxLk4/JwFzo32OaqkIJF0p+N1rG1Pb34Z3U2Ex7BstPIFWIq OiWBMMhShmozlS05YzrVQfcTZajqhojKjfOLaUjQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Breno Leitao , "Paul E. McKenney" , Johannes Weiner , Shakeel Butt , Axel Rasmussen , Barry Song , David Hildenbrand , Kairui Song , Lorenzo Stoakes , Michal Hocko , Wei Xu , Yuanchu Xie , Andrew Morton Subject: [PATCH 5.15 007/935] mm/vmscan: report RCU-tasks quiescent states in shrink_lruvec() Date: Sat, 12 Sep 2026 08:50:37 +0200 Message-ID: <20260912065527.009161641@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065526.833703348@linuxfoundation.org> References: <20260912065526.833703348@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Breno Leitao 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 Link: https://lore.kernel.org/all/amdWVTs0WKOxguxP@gmail.com/ [1] Signed-off-by: Breno Leitao Reviewed-by: Paul E. McKenney Acked-by: Johannes Weiner Acked-by: Shakeel Butt Cc: Axel Rasmussen Cc: Barry Song Cc: David Hildenbrand Cc: Kairui Song Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Wei Xu Cc: Yuanchu Xie Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2771,7 +2771,7 @@ static void shrink_lruvec(struct lruvec } } - cond_resched(); + cond_resched_tasks_rcu_qs(); if (nr_reclaimed < nr_to_reclaim || proportional_reclaim) continue;