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]) by smtp.lore.kernel.org (Postfix) with ESMTP id EAC49CCA47B for ; Wed, 6 Jul 2022 03:00:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 613288E0002; Tue, 5 Jul 2022 23:00:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5C2CE8E0001; Tue, 5 Jul 2022 23:00:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4B1B48E0002; Tue, 5 Jul 2022 23:00:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 3E71E8E0001 for ; Tue, 5 Jul 2022 23:00:46 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 112979AA for ; Wed, 6 Jul 2022 03:00:46 +0000 (UTC) X-FDA: 79655172492.19.FCB465A Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf05.hostedemail.com (Postfix) with ESMTP id A098B10000E for ; Wed, 6 Jul 2022 03:00:45 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3377B61A05; Wed, 6 Jul 2022 03:00:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30997C341C7; Wed, 6 Jul 2022 03:00:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1657076443; bh=p9zi6uyM9qZDm3W0u/jsISQwFAYeuS6nldtEVEqNG/E=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Rt/h9LdUOjMjJYbJ2H8AHVZ59vIHrgzVmYFUT5T9rfYDXGF2TXl6GJtUTSbGD+Xsv R7Twty8/1D88fxTyrvcgCU4W2qvrjUYDAGMI5sGnHaVX/xfY88uNktnLe2dyLI/cqk okhBcnw6gUg1JOHo8MX6rjp0Vjo+rk76AfiFT6k4= Date: Tue, 5 Jul 2022 20:00:42 -0700 From: Andrew Morton To: Muchun Song Cc: Matthew Wilcox , jgg@ziepe.ca, jhubbard@nvidia.com, william.kucharski@oracle.com, dan.j.williams@intel.com, jack@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev, stable@vger.kernel.org Subject: Re: [PATCH v2] mm: fix missing wake-up event for FSDAX pages Message-Id: <20220705200042.26ddd5e2e106df4e65adcc74@linux-foundation.org> In-Reply-To: References: <20220705123532.283-1-songmuchun@bytedance.com> <20220705141819.804eb972d43be3434dc70192@linux-foundation.org> <20220705164710.9541b5cf0e5819193213ea5c@linux-foundation.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657076445; a=rsa-sha256; cv=none; b=Qx2OfdQ2LBs+aHMlQBiWOC2Y7l5Lf2pqUtm2wQiIwO4O1HJkAFuehBsMfm96cbmnLjGdiQ LANd/rM7X3LMHZF6TfdUqmmOPxRQDQAW9un59uxWn40GFMzG0BAdJYuF8PDUFXI0IPKaqS +PkSS1YFFwKgHJDVqTwEqNyVzAXP0to= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="Rt/h9LdU"; dmarc=none; spf=pass (imf05.hostedemail.com: domain of akpm@linux-foundation.org designates 139.178.84.217 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=1657076445; 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=RdTiEXVbk4pHvsnsNp66JjnEAqcfiqNBmnnimA+BlwE=; b=OIid12rXpWD7aGqAH9rnDzRDp/yC1KQrgBnJcDmY23VVNCN6z0yHZ16l1zbSRNc0a9anc5 1FhnPjI50Pope5TPdJRV2DZEJN3cJURrhkV0ClSXCLRIwmDylawFmAksU2WUPrLi55IkFj O2QoWSb40rR2tJdQxmoHUvD6XNNnYBo= X-Stat-Signature: i9g1meofa1pqssy6xnshc3j3whby3fzz X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A098B10000E Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="Rt/h9LdU"; dmarc=none; spf=pass (imf05.hostedemail.com: domain of akpm@linux-foundation.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-HE-Tag: 1657076445-592475 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 6 Jul 2022 10:47:32 +0800 Muchun Song wrote: > > If this wakeup is not one of these, then are there reports from the > > softlockup detector? > > > > Do we have reports of processes permanently stuck in D state? > > > > No. The task is in an TASK_INTERRUPTIBLE state (see __fuse_dax_break_layouts). > The hung task reporter only reports D task (TASK_UNINTERRUPTIBLE). Thanks, I updated the changelog a bit. : FSDAX page refcounts are 1-based, rather than 0-based: if refcount is : 1, then the page is freed. The FSDAX pages can be pinned through GUP, : then they will be unpinned via unpin_user_page() using a folio variant : to put the page, however, folio variants did not consider this special : case, the result will be to miss a wakeup event (like the user of : __fuse_dax_break_layouts()). This results in a task being permanently : stuck in TASK_INTERRUPTIBLE state. : : Since FSDAX pages are only possibly obtained by GUP users, so fix GUP : instead of folio_put() to lower overhead. I believe these details are helpful for -stable maintainers who are wondering why they were sent stuff. Also for maintainers of downstreeam older kernels who are scratching heads over some user bug report, trying to find a patch which might fix it - for this they want to see a description of the user-visible effects, for matching with that bug report.