From patchwork Mon Dec 12 09:38:42 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qu Wenruo X-Patchwork-Id: 9470285 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 AAD2F607D6 for ; Mon, 12 Dec 2016 09:38:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A3C8D28443 for ; Mon, 12 Dec 2016 09:38:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 9881028452; Mon, 12 Dec 2016 09:38:54 +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=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham 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 1BF7E28451 for ; Mon, 12 Dec 2016 09:38:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932395AbcLLJiw (ORCPT ); Mon, 12 Dec 2016 04:38:52 -0500 Received: from cn.fujitsu.com ([222.73.24.84]:49015 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S932383AbcLLJit (ORCPT ); Mon, 12 Dec 2016 04:38:49 -0500 X-IronPort-AV: E=Sophos;i="5.20,367,1444665600"; d="scan'208";a="1015413" Received: from unknown (HELO cn.fujitsu.com) ([10.167.250.3]) by song.cn.fujitsu.com with ESMTP; 12 Dec 2016 17:38:44 +0800 Received: from localhost.localdomain (unknown [10.167.226.34]) by cn.fujitsu.com (Postfix) with ESMTP id 3908741B4BD3; Mon, 12 Dec 2016 17:38:46 +0800 (CST) From: Qu Wenruo To: linux-btrfs@vger.kernel.org, dsterba@suse.cz, clm@fb.com Subject: [PATCH 2/3] btrfs: scrub: Fix RAID56 recovery race condition Date: Mon, 12 Dec 2016 17:38:42 +0800 Message-Id: <20161212093843.8878-3-quwenruo@cn.fujitsu.com> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161212093843.8878-1-quwenruo@cn.fujitsu.com> References: <20161212093843.8878-1-quwenruo@cn.fujitsu.com> MIME-Version: 1.0 X-yoursite-MailScanner-ID: 3908741B4BD3.ACCFA X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: quwenruo@cn.fujitsu.com Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When scrubbing a RAID5 which has recoverable data corruption (only one data stripe is corrupted), sometimes scrub will report more csum errors than expected. Sometimes even unrecoverable error will be reported. The problem can be easily reproduced by the following steps: 1) Create a btrfs with RAID5 data profile with 3 devs 2) Mount it with nospace_cache or space_cache=v2 To avoid extra data space usage. 3) Create a 128K file and sync the fs, unmount it Now the 128K file lies at the beginning of the data chunk 4) Locate the physical bytenr of data chunk on dev3 Dev3 is the 1st data stripe. 5) Corrupt the first 64K of the data chunk stripe on dev3 6) Mount the fs and scrub it The correct csum error number should be 16(assuming using x86_64). Larger csum error number can be reported in a 1/3 chance. And unrecoverable error can also be reported in a 1/10 chance. The root cause of the problem is RAID5/6 recover code has race condition, due to the fact that full scrub is initiated per device. While for other mirror based profiles, each mirror is independent with each other, so race won't cause any big problem. For example: Corrupted | Correct | Correct | | Scrub dev3 (D1) | Scrub dev2 (D2) | Scrub dev1(P) | ------------------------------------------------------------------------ Read out D1 |Read out D2 |Read full stripe | Check csum |Check csum |Check parity | Csum mismatch |Csum match, continue |Parity mismatch | handle_errored_block | |handle_errored_block | Read out full stripe | | Read out full stripe| D1 csum error(err++) | | D1 csum error(err++)| Recover D1 | | Recover D1 | So D1's csum error is accounted twice, just because handle_errored_block() doesn't have enough protect, and race can happen. On even worse case, for example D1's recovery code is re-writing D1/D2/P, and P's recovery code is just reading out full stripe, then we can cause unrecoverable error. This patch will use previously introduced lock_full_stripe() and unlock_full_stripe() to protect the whole scrub_handle_errored_block() function for RAID56 recovery. So no extra csum error nor unrecoverable error. Reported-by: Goffredo Baroncelli Signed-off-by: Qu Wenruo --- fs/btrfs/scrub.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index 2b9555c..5b2f94a 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -1067,6 +1067,7 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check) unsigned int have_csum; struct scrub_block *sblocks_for_recheck; /* holds one for each mirror */ struct scrub_block *sblock_bad; + int lock_ret; int ret; int mirror_index; int page_num; @@ -1096,6 +1097,17 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check) have_csum = sblock_to_check->pagev[0]->have_csum; dev = sblock_to_check->pagev[0]->dev; + /* + * For RAID5/6 race can happen for different dev scrub thread. + * For data corruption, Parity and Data thread will both try + * to recovery the data. + * Race can lead to double added csum error, or even unrecoverable + * error. + */ + ret = lock_full_stripe(fs_info, logical, GFP_NOFS); + if (ret < 0) + return ret; + if (sctx->is_dev_replace && !is_metadata && !have_csum) { sblocks_for_recheck = NULL; goto nodatasum_case; @@ -1430,6 +1442,9 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check) kfree(sblocks_for_recheck); } + lock_ret = unlock_full_stripe(fs_info, logical); + if (lock_ret < 0) + return lock_ret; return 0; }