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 C4705C433EF for ; Thu, 3 Mar 2022 21:30:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236532AbiCCVbX (ORCPT ); Thu, 3 Mar 2022 16:31:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236531AbiCCVbU (ORCPT ); Thu, 3 Mar 2022 16:31:20 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B7010169382 for ; Thu, 3 Mar 2022 13:30:33 -0800 (PST) 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 ams.source.kernel.org (Postfix) with ESMTPS id 0D4FCB825B1 for ; Thu, 3 Mar 2022 21:30:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C0A7C340EC; Thu, 3 Mar 2022 21:30:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646343030; bh=IvX1BiJgviipXegKU6yjvsiv/Z1mRoYaLMflNtLg+yw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kBnWAlsTCTyaZInpwiLdjRBC7/ndMEHjcq9eAWykSX160Dt2JJGa8ekTMmZ829l+9 e3y/H6wwEs97VOBFKQ3RLRhrCYIcOaFPbN16HPCRfmGhzTT99mbhDNHhaUFy8DZn9b vfprHt+YnK72F1EzF6AVtd3KQDoWiBqs15I9m0dYvLM7FCdt10ePTP9jTyIDjYePxG BjR/8Dt7BeLyCFczoSb6LYHohyW5pRgfaIaKb2ypwt5kiM/MFxNw9bobvklerJOckk sWhYSVW3/JK9eWc61f7rqO8Ff3biO4BYjOmqU8ucSM22rRSlOj+/VfV/UqNj6IpFqB aVoLD3Ez5KYRA== Date: Thu, 3 Mar 2022 13:30:28 -0800 From: Jaegeuk Kim To: Chao Yu Cc: Jing Xia , linux-f2fs-devel@lists.sourceforge.net, Zhiguo Niu , linux-kernel@vger.kernel.org Subject: Re: [f2fs-dev] [PATCH] f2fs: fix to avoid potential deadlock Message-ID: References: <51be77f1-6e85-d46d-d0d3-c06d2055a190@kernel.org> <86a175d3-c438-505b-1dbc-4ef6e8b5adcb@kernel.org> <5b5e20d1-877f-b321-b341-c0f233ee976c@kernel.org> <51826b5f-e480-994a-4a72-39ff4572bb3f@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/03, Chao Yu wrote: > On 2022/3/3 3:45, Jaegeuk Kim wrote: > > On 03/02, Chao Yu wrote: > > > On 2022/3/2 13:26, Jaegeuk Kim wrote: > > > > On 03/02, Chao Yu wrote: > > > > > ping, > > > > > > > > > > On 2022/2/25 11:02, Chao Yu wrote: > > > > > > On 2022/2/3 22:57, Chao Yu wrote: > > > > > > > On 2022/2/3 9:51, Jaegeuk Kim wrote: > > > > > > > > On 01/29, Chao Yu wrote: > > > > > > > > > On 2022/1/29 8:37, Jaegeuk Kim wrote: > > > > > > > > > > On 01/28, Chao Yu wrote: > > > > > > > > > > > On 2022/1/28 5:59, Jaegeuk Kim wrote: > > > > > > > > > > > > On 01/27, Chao Yu wrote: > > > > > > > > > > > > > Quoted from Jing Xia's report, there is a potential deadlock may happen > > > > > > > > > > > > > between kworker and checkpoint as below: > > > > > > > > > > > > > > > > > > > > > > > > > > [T:writeback]                [T:checkpoint] > > > > > > > > > > > > > - wb_writeback > > > > > > > > > > > > >     - blk_start_plug > > > > > > > > > > > > > bio contains NodeA was plugged in writeback threads > > > > > > > > > > > > > > > > > > > > > > > > I'm still trying to understand more precisely. So, how is it possible to > > > > > > > > > > > > have bio having node write in this current context? > > > > > > > > > > > > > > > > > > > > > > IMO, after above blk_start_plug(), it may plug some inode's node page in kworker > > > > > > > > > > > during writebacking node_inode's data page (which should be node page)? > > > > > > > > > > > > > > > > > > > > Wasn't that added into a different task->plug? > > > > > > > > > > > > > > > > > > I'm not sure I've got your concern correctly... > > > > > > > > > > > > > > > > > > Do you mean NodeA and other IOs from do_writepages() were plugged in > > > > > > > > > different local plug variables? > > > > > > > > > > > > > > > > I think so. > > > > > > > > > > > > > > I guess block plug helper says it doesn't allow to use nested plug, so there > > > > > > > is only one plug in kworker thread? > > > > > > > > Is there only one kworker thread that flushes node and inode pages? > > > > > > IIRC, =one kworker per block device? > > > > If there's one kworker only, f2fs_write_node_pages() should have flushed its > > plug? > > No, f2fs_write_node_pages() failed to attach local plug into current->plug due to > current has attached plug from wb_writeback(), and also, f2fs_write_node_pages() > will fail to flush current->plug due to its local plug doesn't match current->plug. > > void blk_start_plug_nr_ios() > { > if (tsk->plug) > return; > ... > } > > void blk_finish_plug(struct blk_plug *plug) > { > if (plug == current->plug) { > __blk_flush_plug(plug, false); > current->plug = NULL; > } > } Ah, okay. Now I see. Thanks for the chasing down. > > Thanks, > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > void blk_start_plug_nr_ios(struct blk_plug *plug, unsigned short nr_ios) > > > > > > > { > > > > > > >      struct task_struct *tsk = current; > > > > > > > > > > > > > >      /* > > > > > > >       * If this is a nested plug, don't actually assign it. > > > > > > >       */ > > > > > > >      if (tsk->plug) > > > > > > >          return; > > > > > > > ... > > > > > > > } > > > > > > > > > > > > Any further comments? > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >                     - do_writepages  -- sync write inodeB, inc wb_sync_req[DATA] > > > > > > > > > > > > >                      - f2fs_write_data_pages > > > > > > > > > > > > >                       - f2fs_write_single_data_page -- write last dirty page > > > > > > > > > > > > >                        - f2fs_do_write_data_page > > > > > > > > > > > > >                         - set_page_writeback  -- clear page dirty flag and > > > > > > > > > > > > >                         PAGECACHE_TAG_DIRTY tag in radix tree > > > > > > > > > > > > >                         - f2fs_outplace_write_data > > > > > > > > > > > > >                          - f2fs_update_data_blkaddr > > > > > > > > > > > > >                           - f2fs_wait_on_page_writeback -- wait NodeA to writeback here > > > > > > > > > > > > >                        - inode_dec_dirty_pages > > > > > > > > > > > > >     - writeback_sb_inodes > > > > > > > > > > > > >      - writeback_single_inode > > > > > > > > > > > > >       - do_writepages > > > > > > > > > > > > >        - f2fs_write_data_pages -- skip writepages due to wb_sync_req[DATA] > > > > > > > > > > > > >         - wbc->pages_skipped += get_dirty_pages() -- PAGECACHE_TAG_DIRTY is not set but get_dirty_pages() returns one > > > > > > > > > > > > >      - requeue_inode -- requeue inode to wb->b_dirty queue due to non-zero.pages_skipped > > > > > > > > > > > > >     - blk_finish_plug > > > > > > > > > > > > > > > > > > > > > > > > > > Let's try to avoid deadlock condition by forcing unplugging previous bio via > > > > > > > > > > > > > blk_finish_plug(current->plug) once we'v skipped writeback in writepages() > > > > > > > > > > > > > due to valid sbi->wb_sync_req[DATA/NODE]. > > > > > > > > > > > > > > > > > > > > > > > > > > Fixes: 687de7f1010c ("f2fs: avoid IO split due to mixed WB_SYNC_ALL and WB_SYNC_NONE") > > > > > > > > > > > > > Signed-off-by: Zhiguo Niu > > > > > > > > > > > > > Signed-off-by: Jing Xia > > > > > > > > > > > > > Signed-off-by: Chao Yu > > > > > > > > > > > > > --- > > > > > > > > > > > > >     fs/f2fs/data.c | 6 +++++- > > > > > > > > > > > > >     fs/f2fs/node.c | 6 +++++- > > > > > > > > > > > > >     2 files changed, 10 insertions(+), 2 deletions(-) > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c > > > > > > > > > > > > > index 76d6fe7b0c8f..932a4c81acaf 100644 > > > > > > > > > > > > > --- a/fs/f2fs/data.c > > > > > > > > > > > > > +++ b/fs/f2fs/data.c > > > > > > > > > > > > > @@ -3174,8 +3174,12 @@ static int __f2fs_write_data_pages(struct address_space *mapping, > > > > > > > > > > > > >         /* to avoid spliting IOs due to mixed WB_SYNC_ALL and WB_SYNC_NONE */ > > > > > > > > > > > > >         if (wbc->sync_mode == WB_SYNC_ALL) > > > > > > > > > > > > >             atomic_inc(&sbi->wb_sync_req[DATA]); > > > > > > > > > > > > > -    else if (atomic_read(&sbi->wb_sync_req[DATA])) > > > > > > > > > > > > > +    else if (atomic_read(&sbi->wb_sync_req[DATA])) { > > > > > > > > > > > > > +        /* to avoid potential deadlock */ > > > > > > > > > > > > > +        if (current->plug) > > > > > > > > > > > > > +            blk_finish_plug(current->plug); > > > > > > > > > > > > >             goto skip_write; > > > > > > > > > > > > > +    } > > > > > > > > > > > > >         if (__should_serialize_io(inode, wbc)) { > > > > > > > > > > > > >             mutex_lock(&sbi->writepages); > > > > > > > > > > > > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c > > > > > > > > > > > > > index 556fcd8457f3..69c6bcaf5aae 100644 > > > > > > > > > > > > > --- a/fs/f2fs/node.c > > > > > > > > > > > > > +++ b/fs/f2fs/node.c > > > > > > > > > > > > > @@ -2106,8 +2106,12 @@ static int f2fs_write_node_pages(struct address_space *mapping, > > > > > > > > > > > > >         if (wbc->sync_mode == WB_SYNC_ALL) > > > > > > > > > > > > >             atomic_inc(&sbi->wb_sync_req[NODE]); > > > > > > > > > > > > > -    else if (atomic_read(&sbi->wb_sync_req[NODE])) > > > > > > > > > > > > > +    else if (atomic_read(&sbi->wb_sync_req[NODE])) { > > > > > > > > > > > > > +        /* to avoid potential deadlock */ > > > > > > > > > > > > > +        if (current->plug) > > > > > > > > > > > > > +            blk_finish_plug(current->plug); > > > > > > > > > > > > >             goto skip_write; > > > > > > > > > > > > > +    } > > > > > > > > > > > > >         trace_f2fs_writepages(mapping->host, wbc, NODE); > > > > > > > > > > > > > -- > > > > > > > > > > > > > 2.32.0 > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > > Linux-f2fs-devel mailing list > > > > > > > Linux-f2fs-devel@lists.sourceforge.net > > > > > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > Linux-f2fs-devel mailing list > > > > > > Linux-f2fs-devel@lists.sourceforge.net > > > > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel