From patchwork Tue Jan 29 10:07:33 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Miao Xie X-Patchwork-Id: 2060771 Return-Path: X-Original-To: patchwork-linux-btrfs@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id 85192DF23E for ; Tue, 29 Jan 2013 10:06:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753256Ab3A2KG4 (ORCPT ); Tue, 29 Jan 2013 05:06:56 -0500 Received: from cn.fujitsu.com ([222.73.24.84]:48903 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753116Ab3A2KGy (ORCPT ); Tue, 29 Jan 2013 05:06:54 -0500 X-IronPort-AV: E=Sophos;i="4.84,559,1355068800"; d="scan'208";a="6660397" Received: from unknown (HELO tang.cn.fujitsu.com) ([10.167.250.3]) by song.cn.fujitsu.com with ESMTP; 29 Jan 2013 18:04:42 +0800 Received: from fnstmail02.fnst.cn.fujitsu.com (tang.cn.fujitsu.com [127.0.0.1]) by tang.cn.fujitsu.com (8.14.3/8.13.1) with ESMTP id r0TA6qvV020489 for ; Tue, 29 Jan 2013 18:06:52 +0800 Received: from [10.167.225.199] ([10.167.225.199]) by fnstmail02.fnst.cn.fujitsu.com (Lotus Domino Release 8.5.3) with ESMTP id 2013012918054709-137158 ; Tue, 29 Jan 2013 18:05:47 +0800 Message-ID: <51079F65.5050700@cn.fujitsu.com> Date: Tue, 29 Jan 2013 18:07:33 +0800 From: Miao Xie Reply-To: miaox@cn.fujitsu.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Linux Btrfs Subject: [PATCH V2 05/10] Btrfs: protect fs_info->alloc_start References: <51079D72.7000301@cn.fujitsu.com> In-Reply-To: <51079D72.7000301@cn.fujitsu.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2013/01/29 18:05:47, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2013/01/29 18:05:47, Serialize complete at 2013/01/29 18:05:47 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org fs_info->alloc_start is a 64bits variant, can be accessed by multi-task, but it is not protected strictly, it can be changed while we are accessing it. On 32bit machine, we will get wrong value because we access it by two instructions.(In fact, it is also possible that the same problem happens on the 64bit machine, because the compiler may split the 64bit operation into two 32bit operation.) For example: Assuming -> alloc_start is 0x0000 0000 0001 0000 at the beginning, then we remount and set ->alloc_start to 0x0000 0100 0000 0000. Task0 Task1 load high 32 bits set high 32 bits set low 32 bits load low 32 bits Task1 will get 0. This patch fixes this problem by using two locks to protect it fs_info->chunk_mutex sb->s_umount On the read side, we just need get one of these two locks, and on the write side, we must lock all of them. Signed-off-by: Miao Xie --- Changelog v1 -> v2: - modify the changelog and make it more clear and stringency. --- fs/btrfs/ctree.h | 10 ++++++++++ fs/btrfs/super.c | 4 ++++ 2 files changed, 14 insertions(+) diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 3e672916..201be7d 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -1295,6 +1295,16 @@ struct btrfs_fs_info { * so it is also safe. */ u64 max_inline; + /* + * Protected by ->chunk_mutex and sb->s_umount. + * + * The reason that we use two lock to protect it is because only + * remount and mount operations can change it and these two operations + * are under sb->s_umount, but the read side (chunk allocation) can not + * acquire sb->s_umount or the deadlock would happen. So we use two + * locks to protect it. On the write side, we must acquire two locks, + * and on the read side, we just need acquire one of them. + */ u64 alloc_start; struct btrfs_transaction *running_transaction; wait_queue_head_t transaction_throttle; diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index d8982e9..c96f132 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -519,7 +519,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options) case Opt_alloc_start: num = match_strdup(&args[0]); if (num) { + mutex_lock(&info->chunk_mutex); info->alloc_start = memparse(num, NULL); + mutex_unlock(&info->chunk_mutex); kfree(num); printk(KERN_INFO "btrfs: allocations start at %llu\n", @@ -1289,7 +1291,9 @@ restore: fs_info->mount_opt = old_opts; fs_info->compress_type = old_compress_type; fs_info->max_inline = old_max_inline; + mutex_lock(&fs_info->chunk_mutex); fs_info->alloc_start = old_alloc_start; + mutex_unlock(&fs_info->chunk_mutex); btrfs_resize_thread_pool(fs_info, old_thread_pool_size, fs_info->thread_pool_size); fs_info->metadata_ratio = old_metadata_ratio;