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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1BEBC2BBCD for ; Wed, 16 Dec 2020 17:18:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 85B0A23382 for ; Wed, 16 Dec 2020 17:18:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727044AbgLPRSi (ORCPT ); Wed, 16 Dec 2020 12:18:38 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:30160 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726906AbgLPRSh (ORCPT ); Wed, 16 Dec 2020 12:18:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608139030; h=from:from: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; bh=8FGLJKguNbMK2gP5Em1yZc1NF7tx47dbxS41Hnm91nE=; b=Wlklmu+wxKDOS1wHH2iZH0xg7DFZZ4Bdj6U3XGQTAB5wN7vrwwTQ0Y2E6kt42SPtfBJ+p0 bnj1gEJweblvgo5oXylr/kqlpYcfvY84NhblML+VpYDBZGQFnVwvU7JV6l2Vchr3VaKbwj I40GQkihqz7Cn8ycYwDmsJhn5msYrBA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-301-5d8WtccSMDWQqSS-Qb92aw-1; Wed, 16 Dec 2020 12:17:06 -0500 X-MC-Unique: 5d8WtccSMDWQqSS-Qb92aw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E4B15803F49; Wed, 16 Dec 2020 17:16:19 +0000 (UTC) Received: from horse.redhat.com (ovpn-112-114.rdu2.redhat.com [10.10.112.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9207360BF3; Wed, 16 Dec 2020 17:16:19 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id DFC74220BCF; Wed, 16 Dec 2020 12:16:18 -0500 (EST) Date: Wed, 16 Dec 2020 12:16:18 -0500 From: Vivek Goyal To: Jeff Layton Cc: Linux fsdevel mailing list , linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, miklos@szeredi.hu, amir73il@gmail.com, willy@infradead.org, jack@suse.cz, sargun@sargun.me Subject: Re: [PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs() Message-ID: <20201216171618.GB3177@redhat.com> References: <20201216143802.GA10550@redhat.com> <132c8c1e1ab82f5a640ff1ede6bb844885d46e68.camel@kernel.org> <20201216151409.GA3177@redhat.com> <2b48fe655bd1f821cf575028bc6f811934dad847.camel@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2b48fe655bd1f821cf575028bc6f811934dad847.camel@kernel.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org On Wed, Dec 16, 2020 at 10:53:16AM -0500, Jeff Layton wrote: > On Wed, 2020-12-16 at 10:44 -0500, Jeff Layton wrote: > > On Wed, 2020-12-16 at 10:14 -0500, Vivek Goyal wrote: > > > On Wed, Dec 16, 2020 at 09:57:49AM -0500, Jeff Layton wrote: > > > > On Wed, 2020-12-16 at 09:38 -0500, Vivek Goyal wrote: > > > > > I see that current implementation of __sync_filesystem() ignores the > > > > > return code from ->sync_fs(). I am not sure why that's the case. > > > > > > > > > > Ignoring ->sync_fs() return code is problematic for overlayfs where > > > > > it can return error if sync_filesystem() on upper super block failed. > > > > > That error will simply be lost and sycnfs(overlay_fd), will get > > > > > success (despite the fact it failed). > > > > > > > > > > I am assuming that we want to continue to call __sync_blockdev() > > > > > despite the fact that there have been errors reported from > > > > > ->sync_fs(). So I wrote this simple patch which captures the > > > > > error from ->sync_fs() but continues to call __sync_blockdev() > > > > > and returns error from sync_fs() if there is one. > > > > > > > > > > There might be some very good reasons to not capture ->sync_fs() > > > > > return code, I don't know. Hence thought of proposing this patch. > > > > > Atleast I will get to know the reason. I still need to figure > > > > > a way out how to propagate overlay sync_fs() errors to user > > > > > space. > > > > > > > > > > Signed-off-by: Vivek Goyal > > > > > --- > > > > >  fs/sync.c | 8 ++++++-- > > > > >  1 file changed, 6 insertions(+), 2 deletions(-) > > > > > > > > > > Index: redhat-linux/fs/sync.c > > > > > =================================================================== > > > > > --- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653 -0500 > > > > > +++ redhat-linux/fs/sync.c 2020-12-16 09:23:42.499853207 -0500 > > > > > @@ -30,14 +30,18 @@ > > > > >   */ > > > > >  static int __sync_filesystem(struct super_block *sb, int wait) > > > > >  { > > > > > + int ret, ret2; > > > > > + > > > > >   if (wait) > > > > >   sync_inodes_sb(sb); > > > > >   else > > > > >   writeback_inodes_sb(sb, WB_REASON_SYNC); > > > > >   > > > > > > > > > >   if (sb->s_op->sync_fs) > > > > > - sb->s_op->sync_fs(sb, wait); > > > > > - return __sync_blockdev(sb->s_bdev, wait); > > > > > + ret = sb->s_op->sync_fs(sb, wait); > > > > > + ret2 = __sync_blockdev(sb->s_bdev, wait); > > > > > + > > > > > + return ret ? ret : ret2; > > > > >  } > > > > >   > > > > > > > > > >  /* > > > > > > > > > > > > > I posted a patchset that took a similar approach a couple of years ago, > > > > and we decided not to go with it [1]. > > > > > > > > While it's not ideal to ignore the error here, I think this is likely to > > > > break stuff. > > > > > > So one side affect I see is that syncfs() might start returning errors > > > in some cases which were not reported at all. I am wondering will that > > > count as breakage. > > > > > > > What may be better is to just make sync_fs void return, so > > > > people don't think that returned errors there mean anything. > > > > > > May be. > > > > > > But then question remains that how do we return error to user space > > > in syncfs(fd) for overlayfs. I will not be surprised if other > > > filesystems want to return errors as well. > > > > > > Shall I create new helpers and call these in case of syncfs(). But > > > that too will start returning new errors on syncfs(). So it does > > > not solve that problem (if it is a problem). > > > > > > Or we can define a new super block op say ->sync_fs2() and call that > > > first and in that case capture return code. That way it will not > > > impact existing cases and overlayfs can possibly make use of > > > ->sync_fs2() and return error. IOW, impact will be limited to > > > only file systems which chose to implement ->sync_fs2(). > > > > > > Thanks > > > Vivek > > > > > > > Sure, it's possible to add a sb->sync_fs2, but the problem is that > > sync_fs is a superblock op, and is missing a lot of important context > > about how it got called. > > > > syncfs(2) syscall takes a file descriptor argument. I'd add a new f_op- > > > syncfs vector and turn most of the current guts of the syncfs syscall > > into a generic_syncfs() that gets called when f_op->syncfs isn't > > defined. > > > > Overlayfs could then add a ->syncfs op that would give it control over > > what error gets returned. With that, you could basically leave the old > > sb->sync_fs routine alone. > > > > I think that's probably the safest approach for allowing overlayfs to > > propagate syncfs errors from the upper layer to the overlay. > > > > To be clear, I mean something like this (draft, untested) patch. You'd > also need to add a new ->syncfs op for overlayfs, and that could just do > a check_and_advance against the upper layer sb's errseq_t after calling > sync_filesystem. Hi Jeff, This sounds interesting. Should work for overlayfs. Will make overlayfs changes. So basically a new file operations ->syncfs() which says sync filesystem containing this file. Error code will be captured and returned to user space. Also filesystem is responsible to check for writeback errors. Thanks Vivek > > -----------------------8<------------------------- > > [PATCH] vfs: add new f_op->syncfs vector > > Signed-off-by: Jeff Layton > --- > fs/sync.c | 30 +++++++++++++++++++++--------- > include/linux/fs.h | 1 + > 2 files changed, 22 insertions(+), 9 deletions(-) > > diff --git a/fs/sync.c b/fs/sync.c > index 1373a610dc78..fc7f73762b9e 100644 > --- a/fs/sync.c > +++ b/fs/sync.c > @@ -155,27 +155,39 @@ void emergency_sync(void) > } > } > > +static int generic_syncfs(struct file *file) > +{ > + int ret, ret2; > + struct super_block *sb = file->f_path.dentry->d_sb; > + > + down_read(&sb->s_umount); > + ret = sync_filesystem(sb); > + up_read(&sb->s_umount); > + > + ret2 = errseq_check_and_advance(&sb->s_wb_err, &f.file->f_sb_err); > + > + fdput(f); > + return ret ? ret : ret2; > +} > + > /* > * sync a single super > */ > SYSCALL_DEFINE1(syncfs, int, fd) > { > struct fd f = fdget(fd); > - struct super_block *sb; > - int ret, ret2; > + int ret; > > if (!f.file) > return -EBADF; > - sb = f.file->f_path.dentry->d_sb; > > - down_read(&sb->s_umount); > - ret = sync_filesystem(sb); > - up_read(&sb->s_umount); > - > - ret2 = errseq_check_and_advance(&sb->s_wb_err, &f.file->f_sb_err); > + if (f.file->f_op->syncfs) > + ret = f.file->f_op->syncfs(f.file); > + else > + ret = generic_syncfs(f.file); > > fdput(f); > - return ret ? ret : ret2; > + return ret; > } > > /** > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 8667d0cdc71e..6710469b7e33 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1859,6 +1859,7 @@ struct file_operations { > struct file *file_out, loff_t pos_out, > loff_t len, unsigned int remap_flags); > int (*fadvise)(struct file *, loff_t, loff_t, int); > + int (*syncfs)(struct file *); > } __randomize_layout; > > struct inode_operations { > -- > 2.29.2 > > >