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Tue, 31 Aug 2021 01:22:17 +0000 From: Anand Jain To: linux-btrfs@vger.kernel.org, dsterba@suse.com Cc: l@damenly.su Subject: [PATCH RFC V5 2/2] btrfs: consolidate device_list_mutex in prepare_sprout to its parent Date: Tue, 31 Aug 2021 09:21:29 +0800 Message-Id: X-Mailer: git-send-email 2.31.1 In-Reply-To: References: Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: SG2PR03CA0144.apcprd03.prod.outlook.com (2603:1096:4:c8::17) To MN2PR10MB4128.namprd10.prod.outlook.com (2603:10b6:208:1d2::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from dev.sg.oracle.com (203.116.164.13) by SG2PR03CA0144.apcprd03.prod.outlook.com (2603:1096:4:c8::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4478.8 via Frontend Transport; Tue, 31 Aug 2021 01:22:15 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 7781171c-7416-4528-2863-08d96c1dc54e X-MS-TrafficTypeDiagnostic: MN2PR10MB4350: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8882; 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Both btrfs_prepare_sprout() and btrfs_init_new_device() needs device_list_mutex. But they are holding it sequentially, thus creates a small window to an opportunity to race. Close this opportunity and hold device_list_mutex common to both btrfs_init_new_device() and btrfs_prepare_sprout(). Signed-off-by: Anand Jain --- RFC because IMO the cleanup of device_list_mutex makes sense even though there isn't another thread that could race potentially race as of now. Depends on [PATCH v2] btrfs: fix lockdep warning while mounting sprout fs which removed the device_list_mutex from clone_fs_devices() otherwise this patch will cause a double mutex error. v2: fix the missing mutex_unlock in the error return v3: - v4: - v5: - (Except for the change in below SO comments) fs/btrfs/volumes.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index fa9fe47b5b68..53ead67b625c 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -2369,6 +2369,8 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) u64 super_flags; lockdep_assert_held(&uuid_mutex); + lockdep_assert_held(&fs_devices->device_list_mutex); + if (!fs_devices->seeding) return -EINVAL; @@ -2400,7 +2402,6 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) INIT_LIST_HEAD(&seed_devices->alloc_list); mutex_init(&seed_devices->device_list_mutex); - mutex_lock(&fs_devices->device_list_mutex); list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices, synchronize_rcu); list_for_each_entry(device, &seed_devices->devices, dev_list) @@ -2416,7 +2417,6 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) generate_random_uuid(fs_devices->fsid); memcpy(fs_devices->metadata_uuid, fs_devices->fsid, BTRFS_FSID_SIZE); memcpy(disk_super->fsid, fs_devices->fsid, BTRFS_FSID_SIZE); - mutex_unlock(&fs_devices->device_list_mutex); super_flags = btrfs_super_flags(disk_super) & ~BTRFS_SUPER_FLAG_SEEDING; @@ -2591,10 +2591,12 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path device->dev_stats_valid = 1; set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE); + mutex_lock(&fs_devices->device_list_mutex); if (seeding_dev) { btrfs_clear_sb_rdonly(sb); ret = btrfs_prepare_sprout(fs_info); if (ret) { + mutex_unlock(&fs_devices->device_list_mutex); btrfs_abort_transaction(trans, ret); goto error_trans; } @@ -2604,7 +2606,6 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path device->fs_devices = fs_devices; - mutex_lock(&fs_devices->device_list_mutex); mutex_lock(&fs_info->chunk_mutex); list_add_rcu(&device->dev_list, &fs_devices->devices); list_add(&device->dev_alloc_list, &fs_devices->alloc_list); -- 2.31.1