On Fri, Apr 17, 2015 at 7:26 PM, Josef Bacik <jba...@fb.com> wrote: > On 04/17/2015 02:20 PM, Filipe Manana wrote: >> >> If we have concurrent fsync calls against files living in the same >> subvolume, >> we have some time window where we don't add the collected ordered extents >> to the running transaction's list of ordered extents and return success to >> userspace. This can result in data loss if the ordered extents complete >> after >> the current transaction commits and a power failure happens after the >> current >> transaction commits and before the next one commits. >> >> A sequence of steps that lead to this: >> >> CPU 0 CPU >> 1 >> >> btrfs_sync_file(inode A) >> btrfs_sync_file(inode B) >> btrfs_log_inode_parent() >> btrfs_log_inode_parent() >> >> start_log_trans() >> lock root->log_mutex >> ctx->log_transid = root->log_transid = N >> unlock root->log_mutex >> >> >> start_log_trans() >> lock >> root->log_mutex >> >> ctx->log_transid = root->log_transid = N >> unlock >> root->log_mutex >> >> btrfs_log_inode() >> btrfs_log_inode() >> btrfs_get_logged_extents() >> btrfs_get_logged_extents() >> --> gets orderede extent A -> >> gets ordered extent B >> into local list logged_list >> into local list logged_list >> write items into the log tree write >> items into the log tree >> btrfs_submit_logged_extents(&logged_list) >> --> splices logged_list into >> log_root->logged_list[N % 2] >> (N == log_root->log_transid) >> >> btrfs_sync_log() >> lock root->log_mutex >> >> atomic_set(&root->log_commit[N % 2], 1) >> (N == ctx->log_transid) > > > Except this can't happen, we have a wait_for_writer() in between here that > will wait for CPU 1 to finish doing it's logging since it has already done > it's start_log_trans(). Thanks,
Right, totally forgot that. Thanks for pointing it out Josef. > > Josef > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Filipe David Manana, "Reasonable men adapt themselves to the world. Unreasonable men adapt the world to themselves. That's why all progress depends on unreasonable men." -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
