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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B46F6C433EF for ; Wed, 6 Jul 2022 03:01:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231574AbiGFDBY (ORCPT ); Tue, 5 Jul 2022 23:01:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51704 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231699AbiGFDBG (ORCPT ); Tue, 5 Jul 2022 23:01:06 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 962B71EC4A; Tue, 5 Jul 2022 20:00:44 -0700 (PDT) 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 3037761A1B; 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 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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.