From patchwork Tue Apr 25 16:43:23 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Layton X-Patchwork-Id: 9698759 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 22FDE6020A for ; Tue, 25 Apr 2017 16:43:41 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 10EEE28636 for ; Tue, 25 Apr 2017 16:43:41 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 0540928660; Tue, 25 Apr 2017 16:43:41 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.4 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RCVD_IN_SORBS_SPAM autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 037632865D for ; Tue, 25 Apr 2017 16:43:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1432079AbdDYQnf (ORCPT ); Tue, 25 Apr 2017 12:43:35 -0400 Received: from mail-qt0-f175.google.com ([209.85.216.175]:33676 "EHLO mail-qt0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1432015AbdDYQn2 (ORCPT ); Tue, 25 Apr 2017 12:43:28 -0400 Received: by mail-qt0-f175.google.com with SMTP id m36so144714528qtb.0 for ; Tue, 25 Apr 2017 09:43:28 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:mime-version:content-transfer-encoding; bh=RDKYzyvrZLEgYDx0p1nSsRUI+zHFEoYykzayCZ4YkoE=; b=ZdFQeOeqbe9Z5YsrN+gRa8wKv/FHCsTWTbpl7jiuUTIUVm29fNtZqwaKBlA7xuWOWt izLjqww8MeEWx9KuchzSRtp0mRfAeIHe2mndqGMXGBZPHQK2BmxMYzZsKRLCETtVYaVe lbMhEyZSVzIVchP4uyy1HKUHvxkrdmUAYR5M3unE/U6U2HoBvfqmyqAbZPOhGBI9u9x/ 2qYadtucbbGviwT620S/Rd0bCi7T7xllCOTYMUjFDJ73ahGI53S3WhboxRyriuerJxBp sdzTvAzKrSZM69TeR4uoxKNaWMB/BtCU648jiSy0I+s2dXQIEUtNRlqkWloOApDxgDyK 3ekQ== X-Gm-Message-State: AN3rC/42zxSFpcF7RTihLCcY2micDyC+bn2m5z8bjYsDv1nT3WGp7sRu oIXWDdQs2sR5fLSU X-Received: by 10.200.48.98 with SMTP id g31mr35038237qte.82.1493138607375; Tue, 25 Apr 2017 09:43:27 -0700 (PDT) Received: from tleilax.poochiereds.net ([2606:a000:1125:405b:dece:a663:7b68:bd3e]) by smtp.gmail.com with ESMTPSA id q6sm15361170qtg.39.2017.04.25.09.43.25 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 25 Apr 2017 09:43:26 -0700 (PDT) Message-ID: <1493138603.2758.3.camel@redhat.com> Subject: Re: [PATCH v3 10/20] fuse: set mapping error in writepage_locked when it fails From: Jeff Layton To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-cifs@vger.kernel.org, linux-mm@kvack.org, jfs-discussion@lists.sourceforge.net, linux-xfs@vger.kernel.org, cluster-devel@redhat.com, linux-f2fs-devel@lists.sourceforge.net, v9fs-developer@lists.sourceforge.net, osd-dev@open-osd.org, linux-nilfs@vger.kernel.org, linux-block@vger.kernel.org, dhowells@redhat.com, akpm@linux-foundation.org, hch@infradead.org, ross.zwisler@linux.intel.com, mawilcox@microsoft.com, jack@suse.com, viro@zeniv.linux.org.uk, corbet@lwn.net, neilb@suse.de, clm@fb.com, tytso@mit.edu, axboe@kernel.dk, Jonathan Corbet Date: Tue, 25 Apr 2017 12:43:23 -0400 In-Reply-To: <20170425111903.GI2793@quack2.suse.cz> References: <20170424132259.8680-1-jlayton@redhat.com> <20170424132259.8680-11-jlayton@redhat.com> <20170424160431.GK23988@quack2.suse.cz> <1493054076.2895.17.camel@redhat.com> <20170425081720.GA2793@quack2.suse.cz> <1493116513.2758.1.camel@redhat.com> <20170425111903.GI2793@quack2.suse.cz> X-Mailer: Evolution 3.22.6 (3.22.6-2.fc25) Mime-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Tue, 2017-04-25 at 13:19 +0200, Jan Kara wrote: > On Tue 25-04-17 06:35:13, Jeff Layton wrote: > > On Tue, 2017-04-25 at 10:17 +0200, Jan Kara wrote: > > > On Mon 24-04-17 13:14:36, Jeff Layton wrote: > > > > On Mon, 2017-04-24 at 18:04 +0200, Jan Kara wrote: > > > > > On Mon 24-04-17 09:22:49, Jeff Layton wrote: > > > > > > This ensures that we see errors on fsync when writeback fails. > > > > > > > > > > > > Signed-off-by: Jeff Layton > > > > > > > > > > Hum, but do we really want to clobber mapping errors with temporary stuff > > > > > like ENOMEM? Or do you want to handle that in mapping_set_error? > > > > > > > > > > > > > Right now we don't really have such a thing as temporary errors in the > > > > writeback codepath. If you return an error here, the data doesn't stay > > > > dirty or anything, and I think we want to ensure that that gets reported > > > > via fsync. > > > > > > > > I'd like to see us add better handling for retryable errors for stuff > > > > like ENOMEM or EAGAIN. I think this is the first step toward that > > > > though. Once we have more consistent handling of writeback errors in > > > > general, then we can start doing more interesting things with retryable > > > > errors. > > > > > > > > So yeah, I this is the right thing to do for now. > > > > > > OK, fair enough. And question number 2): > > > > > > Who is actually responsible for setting the error in the mapping when error > > > happens inside ->writepage()? Is it the ->writepage() callback or the > > > caller of ->writepage()? Or something else? Currently it seems to be a > > > strange mix (e.g. mm/page-writeback.c: __writepage() calls > > > mapping_set_error() when ->writepage() returns error) so I'd like to > > > understand what's the plan and have that recorded in the changelogs. > > > > > > > That's an excellent question. > > > > I think we probably want the writepage/launder_page operations to call > > mapping_set_error. That makes it possible for filesystems (e.g. NFS) to > > handle their own error tracking and reporting without using the new > > infrastructure. If they never call mapping_set_error then we'll always > > just return whatever their ->fsync operation returns on an fsync. > > OK, makes sense. It is also in line with what you did for DAX, 9p, or here > for FUSE. So feel free to add: > > Reviewed-by: Jan Kara > > for this patch but please also add a sentense that ->writepage() is > responsible for calling mapping_set_error() if it fails and page is not > redirtied to the changelogs of patches changing writepage handlers. > > > I'll make another pass through the tree and see whether we have some > > mapping_set_error calls that should be removed, and will flesh out > > vfs.txt to state this. Maybe that file needs a whole section on > > writeback error reporting? Hmmm... > > I think it would be nice to have all the logic described in one place. So > +1 from me. > > > That probably also means that I should drop patch 8 from this series > > (mm: ensure that we set mapping error if writeout fails), since that > > should be happening in writepage already. > > Yes. > > Honza (cc'ing Jon since I'm proposing a doc update) Here's what I'm thinking for a vfs.txt update after this series. The section on writeback_control could probably be more specific. ----------------------8<------------------------- diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 94dd27ef4a76..aa912b65792a 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -576,7 +576,23 @@ should clear PG_Dirty and set PG_Writeback. It can be actually written at any point after PG_Dirty is clear. Once it is known to be safe, PG_Writeback is cleared. -Writeback makes use of a writeback_control structure... +Writeback makes use of a writeback_control structure to direct the +operations. This tells the writepage and writepages operations something +about the nature of and reason for the writeback request, and the +constraints under which it is being done. It is also used to track state +between successive writeback requests. + +When there is an error during writeback, then an error should be +reported to fsync on all file descriptors that were open at the time of +the error. This is typically done by setting the wb_err value in the +address_space via mapping_set_error when writeback errors occur. The +vfs-layer fsync code will then report the errors on a per-fd basis. + +Filesystems are free to track errors internally if they choose, but they +should aim to provide the same semantics for error reporting when there +are multiple writers. Filesystems that track their own errors should +avoid calling mapping_set_error in order to ensure that errors stored in +the mapping aren't improperly reported by the generic filesystem code. struct address_space_operations ------------------------------- @@ -888,7 +904,9 @@ otherwise noted. release: called when the last reference to an open file is closed - fsync: called by the fsync(2) system call + fsync: called by the fsync(2) system call. Errors that were previously + recorded using mapping_set_error will automatically be returned to + the application and the file's error sequence advanced. fasync: called by the fcntl(2) system call when asynchronous (non-blocking) mode is enabled for a file