From: Jeff Layton Subject: Re: [PATCH v3 10/20] fuse: set mapping error in writepage_locked when it fails Date: Tue, 25 Apr 2017 06:35:13 -0400 Message-ID: <1493116513.2758.1.camel@redhat.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit 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 To: Jan Kara Return-path: In-Reply-To: <20170425081720.GA2793@quack2.suse.cz> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org 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. 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... 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. > > > > > > > > > --- > > > > fs/fuse/file.c | 1 + > > > > 1 file changed, 1 insertion(+) > > > > > > > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > > > > index ec238fb5a584..07d0efcb050c 100644 > > > > --- a/fs/fuse/file.c > > > > +++ b/fs/fuse/file.c > > > > @@ -1669,6 +1669,7 @@ static int fuse_writepage_locked(struct page *page) > > > > err_free: > > > > fuse_request_free(req); > > > > err: > > > > + mapping_set_error(page->mapping, error); > > > > end_page_writeback(page); > > > > return error; > > > > } > > > > -- > > > > 2.9.3 > > > > > > > > > > > > -- > > Jeff Layton -- Jeff Layton -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org