From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CC237C982D7 for ; Fri, 18 Sep 2026 19:32:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 99E106B0088; Fri, 18 Sep 2026 15:32:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 94F0C6B008A; Fri, 18 Sep 2026 15:32:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8662F6B008C; Fri, 18 Sep 2026 15:32:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 66EB56B0088 for ; Fri, 18 Sep 2026 15:32:43 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 9D0FB140742 for ; Fri, 18 Sep 2026 19:32:42 +0000 (UTC) X-FDA: 85227880164.21.926C1BC Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf29.hostedemail.com (Postfix) with ESMTP id D5648120004 for ; Fri, 18 Sep 2026 19:32:40 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=kr5npqUT; dmarc=none; spf=pass (imf29.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789759961; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=VABaJiNkB+07BojV48SKGNtgg2IwaRyrt+EONkqTGrg=; b=i4vpc4Rx0skXny8kzjECuhCE8/r8Mf2c6B4jJtAyc0q0ju1XmUfLujGXT2cwQM+puTD79L p7apr9Btp+s77QzDSf9JRRKJWpw1Go3fTntu+rYu1CELLOKa4pv2hX+W97gdKyjl3Etmm9 mjTOox+Qs3wh8hfUmyd91LB202mPrnI= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789759961; b=yrbcWpQ8QJKf9v72lDnxtYkN9c6E1lv07afcpYkdBBa0fSTC7JIBz2wYYu9Zxt0JhSojAX WafesJXfdi97tNQ20IMXAKncHOvD1EZd1exSUypCQQF6+YmNoDtUPKBBHParMIXcVulu3B 6smhiUkufCX9TKwIe9ISkcsMi9RG6EM= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=kr5npqUT; dmarc=none; spf=pass (imf29.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 3E663602CC; Fri, 18 Sep 2026 19:32:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B8391F000FF; Fri, 18 Sep 2026 19:32:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789759959; bh=VABaJiNkB+07BojV48SKGNtgg2IwaRyrt+EONkqTGrg=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=kr5npqUTuUYIza0EGwv8Pg0oNpVs/9IBZjeSpnYCPu6IPmMsPIRAUgoG3t7c4L2kz LVnje1t/pJHBSKi241YC/xgs60r2ae+81Xt09eCek58jEYUAcGTfyqSoN/L/TtYEUX HrejmoiEpUBqYcpsbCg8muFi3WxyiezK9mUxrI1w= Date: Fri, 18 Sep 2026 12:32:39 -0700 From: Andrew Morton To: Breno Leitao Cc: Hugh Dickins , Baolin Wang , "Paul E. McKenney" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, stable@vger.kernel.org Subject: Re: [PATCH] mm/shmem: report RCU-tasks quiescent states while undoing a range Message-Id: <20260918123239.8f25b984ca280fcc11ef6e6a@linux-foundation.org> In-Reply-To: <20260918-shmem-tasks-rcu-v1-1-79acf91a2569@debian.org> References: <20260918-shmem-tasks-rcu-v1-1-79acf91a2569@debian.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D5648120004 X-Stat-Signature: f5oqpg856jbtafkjw77sxznkrkjd9a4e X-HE-Tag: 1789759960-526032 X-HE-Meta: U2FsdGVkX19t0loMt+Hs/tDX6OnikvC/q9KXMU4t27htQCXR1hDyCHqO/gNb3DsQmPaVs7oIWT0DD1uXcuHWfOR4kS39eEIVtSoiTFBGc8mr7OUX8vXUHyy7unwUmQogq3A8v81aCbunEcFQn6Ol/ZGchwIy4ykOhmji1BBd5hys/iqcfDMvdGV03osff7jjcG8JxLknOcOTvAUbLAvR9Aau7v0Bxh0XnTwvmmQ+st5XfnETDMdTy9hkq5bFaiBjepKZ9vs+/Rda3tOn0daB2yBDqt+vscqtBHxsn4uonAomIEYDmq1nM/4FO9H61vSktfBQP7s6rVooRYyeVxPvsReE8+qFnbsGyxSp5cmMHjeOs4MjmjLxobpkj3YbgtBPITG2cZBGT8ZHic6j6zdBOm56SC6wBrZxfM7JWfjE1iBOQx3GoW+yN85alhZTzp7FP7SO3fVq7PbuylczoF9E0KyG0leoMNDWtCQHPh53EtcJm7KIgl2fJAKPhJBC8ogZyB7mA7v9tLKfx57yzHsX5RUnUIhp6cIaFZ5VFUpWO1ndP0qMXbiX+0AJYGfbqcByG6Nt/nh31ppqrULO2MPy27e1REg+lX+uII3l9yjBhDea+ka29nS7CqMLQvSuuuiWhwkFGZhdVZSpJ/l8sPb+Woo+Ma+x0nBblhAU5vbtHu+jVFfkmAv9SCWqtr3EWtvZACS6EcbF6WIUM8qMYg5AOS5IpbdYZk8ZXC57Kkz96e/0SbQ2Zc1j0taWQ66OU2pvoFnIcN54fnStXhlFI7vx0bPBb0dmI6/NamSJBF2AQY0geRx/IcdFqNFAJGMkGBl/KJs9KlNiBZiZaA6hPn5AQPpgpH+FWl1SkJqEp+nrN5hVn1P/3E4n+sd5gwbCAbHuCoaCApDr3jXFU5nnkXBcYfXMeMH0dSD8dhgWJuzs0mNuJK7bSdNNi2UfAzv7Np7B4RmniOD1SpT0jLEGPcn F9O9bmQx 9bzJBibMQnnYf25HOFhh96u/zR92zosYUEGWneZpDnISIN9k6DqhcAyYTg++uTbO9f+tJli+BUln4eSmAJc0/91J0ZWHHD9OesEYXSHnD9sYtMFjb+l7qEgF9P75XrFiBFhN66nHrWdUQ3tJAvG09shQhlJb0ghGFrDL9oHHwG/gDcIVcapoMBDrMyEhaH5LYMlNiEylITSC911a37vEWnm18DaI+lVJVlaAY1vCuuhHuPKLI/lSU+Gpyd2ghD/L0j25KJ0UUAoHv8pCXq4VWJlhQAiTCPMVKGUO8kVUw3qvqy/U= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 18 Sep 2026 04:24:37 -0700 Breno Leitao wrote: > This shows up in the Meta fleet on ftruncate() of large tmpfs files: > > INFO: rcu_tasks detected stalls on tasks: > 00000000752fd185: .. nvcsw: 59455/59455 holdout: 1 idle_cpu: -1/0 > task:rocksdb:bottom state:R running task > __folio_split > find_get_entry > find_get_entries > truncate_inode_partial_folio > shmem_undo_range > shmem_setattr > notify_change > do_ftruncate > __x64_sys_ftruncate > do_syscall_64 > > shmem_undo_range() walks the whole of the requested range in folio_batch > sized steps, twice, and its two cond_resched() calls are the only > reschedule points in that walk. > > cond_resched() is not an RCU-tasks quiescent state. Use > cond_resched_tasks_rcu_qs() at both points so the walk reports an > RCU-tasks quiescent state as it proceeds. We keep hitting this. Whyohwhy doesn't cond_resched() imply cond_resched_tasks_rcu_qs(). > Fixes: 8315f42295d2 ("rcu: Add call_rcu_tasks()") > Cc: stable@vger.kernel.org That's 2014. > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1367,7 +1367,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, > } > folio_batch_remove_exceptionals(&fbatch); > folio_batch_release(&fbatch); > - cond_resched(); > + cond_resched_tasks_rcu_qs(); Won't this change remove the cond_resched() function from old kernels which really want it?