From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([222.73.24.84]:8015 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1750920Ab3LCFGy (ORCPT ); Tue, 3 Dec 2013 00:06:54 -0500 Message-ID: <529D66DA.8060407@cn.fujitsu.com> Date: Tue, 03 Dec 2013 13:06:34 +0800 From: Wang Shilong MIME-Version: 1.0 To: bo.li.liu@oracle.com CC: Wang Shilong , linux-btrfs@vger.kernel.org, ochmann@informatik.uni-bonn.de Subject: Re: [PATCH v3] Btrfs: fix wrong super generation mismatch when scrubbing supers References: <1386005619-7750-1-git-send-email-wangshilong1991@gmail.com> <20131203045729.GB18095@localhost.localdomain> In-Reply-To: <20131203045729.GB18095@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hi Liu, On 12/03/2013 12:57 PM, Liu Bo wrote: > On Tue, Dec 03, 2013 at 01:33:39AM +0800, Wang Shilong wrote: >> From: Wang Shilong >> >> We came a race condition when scrubbing superblocks, the story is: >> >> In commiting transaction, we will update last_trans_commited after >> writting superblocks. if a scrub start after writting superblocks >> and before last_trans_commited, generation mismatch happens! >> >> We fix it by protecting writting superblock and updating last_trans_commited >> with tree_log_mutex. >> >> Reported-by: Sebastian Ochmann >> Signed-off-by: Wang Shilong >> --- >> Changelog: >> v2->v3:move tree_log_mutex out of device_list_mutex. >> v1->v2: use right way to fix the problem. >> --- >> fs/btrfs/scrub.c | 11 +++++++---- >> fs/btrfs/transaction.c | 13 ++++++++++--- >> 2 files changed, 17 insertions(+), 7 deletions(-) >> >> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c >> index 561e2f1..a9ed102 100644 >> --- a/fs/btrfs/scrub.c >> +++ b/fs/btrfs/scrub.c >> @@ -2887,6 +2887,7 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start, >> } >> >> >> + mutex_lock(&fs_info->tree_log_mutex); >> mutex_lock(&fs_info->fs_devices->device_list_mutex); >> dev = btrfs_find_device(fs_info, devid, NULL, NULL); >> if (!dev || (dev->missing && !is_dev_replace)) { >> @@ -2932,14 +2933,16 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start, >> atomic_inc(&fs_info->scrubs_running); >> mutex_unlock(&fs_info->scrub_lock); >> >> + /* >> + * holding tree_log_mutex we can avoid generation mismatch while >> + * scrubbing superblocks, see comments in commiting transaction >> + * when updating last_trans_commited. >> + */ >> if (!is_dev_replace) { >> - /* >> - * by holding device list mutex, we can >> - * kick off writing super in log tree sync. >> - */ >> ret = scrub_supers(sctx, dev); >> } >> mutex_unlock(&fs_info->fs_devices->device_list_mutex); >> + mutex_unlock(&fs_info->tree_log_mutex); > IIRC, we already have btrfs_scrub_{pause, continue}() to avoid race > situations between committing transaction and scrub processes, why not use that > instead? btrfs_scrub_{pause,continue} can not stop the following case from happening: thread 1 thread 2 |->write_supers |->start scrub |->using last_trans_commited(not updated yet) when scrubbing supers generation in disk is up to date but in memory is not. |->updating last_trans_commited Pleae correct me if i am wrong here. :-) > > (Actually I don't like adding another lock unless it's been proved necessary > and correct with lockdep.) Right, i should test if it can pass lockdep. Thanks for comments. Wang > > thanks, > -liubo > >> >> if (!ret) >> ret = scrub_enumerate_chunks(sctx, dev, start, end, >> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c >> index c6a872a..052eb22 100644 >> --- a/fs/btrfs/transaction.c >> +++ b/fs/btrfs/transaction.c >> @@ -1898,15 +1898,22 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, >> goto cleanup_transaction; >> } >> >> + btrfs_finish_extent_commit(trans, root); >> + >> + /* >> + * we must gurantee last_trans_commited update is protected by >> + * tree_log_mutex with write_ctree_super together, otherwise, >> + * scubbing super will come in before updating last_trans_commited >> + * and we will get generation mismatch when scrubbing superblocks. >> + */ >> + root->fs_info->last_trans_committed = cur_trans->transid; >> + >> /* >> * the super is written, we can safely allow the tree-loggers >> * to go about their business >> */ >> mutex_unlock(&root->fs_info->tree_log_mutex); >> >> - btrfs_finish_extent_commit(trans, root); >> - >> - root->fs_info->last_trans_committed = cur_trans->transid; >> /* >> * We needn't acquire the lock here because there is no other task >> * which can change it. >> -- >> 1.8.4 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html