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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 1B349C2BA19 for ; Wed, 15 Apr 2020 14:07:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBA1B20775 for ; Wed, 15 Apr 2020 14:07:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2634071AbgDOOHL (ORCPT ); Wed, 15 Apr 2020 10:07:11 -0400 Received: from mx2.suse.de ([195.135.220.15]:40414 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2636412AbgDOOGq (ORCPT ); Wed, 15 Apr 2020 10:06:46 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 97A3CAA7C; Wed, 15 Apr 2020 14:06:43 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 85D601E1250; Wed, 15 Apr 2020 16:06:42 +0200 (CEST) Date: Wed, 15 Apr 2020 16:06:42 +0200 From: Jan Kara To: Jeff Layton Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, andres@anarazel.de, willy@infradead.org, dhowells@redhat.com, hch@infradead.org, jack@suse.cz, akpm@linux-foundation.org, david@fromorbit.com Subject: Re: [PATCH v5 2/2] buffer: record blockdev write errors in super_block that it backs Message-ID: <20200415140642.GK6126@quack2.suse.cz> References: <20200415121300.228017-1-jlayton@kernel.org> <20200415121300.228017-3-jlayton@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200415121300.228017-3-jlayton@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 15-04-20 08:13:00, Jeff Layton wrote: > From: Jeff Layton > > When syncing out a block device (a'la __sync_blockdev), any error > encountered will only be recorded in the bd_inode's mapping. When the > blockdev contains a filesystem however, we'd like to also record the > error in the super_block that's stored there. > > Make mark_buffer_write_io_error also record the error in the > corresponding super_block when a writeback error occurs and the block > device contains a mounted superblock. > > Since superblocks are RCU freed, hold the rcu_read_lock to ensure > that the superblock doesn't go away while we're marking it. > > Signed-off-by: Jeff Layton > --- > fs/buffer.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/fs/buffer.c b/fs/buffer.c > index f73276d746bb..2a4a5cc20418 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -1154,12 +1154,19 @@ EXPORT_SYMBOL(mark_buffer_dirty); > > void mark_buffer_write_io_error(struct buffer_head *bh) > { > + struct super_block *sb; > + > set_buffer_write_io_error(bh); > /* FIXME: do we need to set this in both places? */ > if (bh->b_page && bh->b_page->mapping) > mapping_set_error(bh->b_page->mapping, -EIO); > if (bh->b_assoc_map) > mapping_set_error(bh->b_assoc_map, -EIO); > + rcu_read_lock(); > + sb = bh->b_bdev->bd_super; You still need READ_ONCE() here. Otherwise the dereference below can still result in refetch and NULL ptr deref. Honza > + if (sb) > + errseq_set(&sb->s_wb_err, -EIO); > + rcu_read_unlock(); > } > EXPORT_SYMBOL(mark_buffer_write_io_error); > > -- > 2.25.2 > -- Jan Kara SUSE Labs, CR