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Wed, 25 Aug 2021 02:00:24 +0000 Subject: Re: [PATCH v2 3/7] btrfs: do not read super look for a device path To: Josef Bacik References: <26639cd9f337a84b432b6627cd7c17b3d6d51e34.1627419595.git.josef@toxicpanda.com> From: Anand Jain Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com Message-ID: <41d2c028-6af5-ab2b-91fa-1090d4258ba9@oracle.com> Date: Wed, 25 Aug 2021 10:00:16 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: <26639cd9f337a84b432b6627cd7c17b3d6d51e34.1627419595.git.josef@toxicpanda.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SG2P153CA0006.APCP153.PROD.OUTLOOK.COM (2603:1096::16) To MN2PR10MB4128.namprd10.prod.outlook.com (2603:10b6:208:1d2::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.10.109] (39.109.186.25) by SG2P153CA0006.APCP153.PROD.OUTLOOK.COM (2603:1096::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4478.1 via Frontend Transport; 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All we need to do if we're given a path > is look through the fs_devices on our file system and use that device if > we find it, reading the super block is just silly. The device path as stored in our fs_devices can differ from the path provided by the user for the same device (for example, dm, lvm). btrfs-progs sanitize the device path but, others (for example, an ioctl test case) might not. And the path lookup would fail. Also, btrfs dev scan can update the device path anytime, even after it is mounted. Fixing that failed the subsequent subvolume mounts (if I remember correctly). > This fixes the case where we end up with our sb write "lock" getting the > dependency of the block device ->open_mutex, which resulted in the > following lockdep splat Can we do.. btrfs_exclop_start() :: find device part (read sb) :: mnt_want_write_file()? Thanks, Anand > > ====================================================== > WARNING: possible circular locking dependency detected > 5.14.0-rc2+ #405 Not tainted > ------------------------------------------------------ > losetup/11576 is trying to acquire lock: > ffff9bbe8cded938 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x67/0x5e0 > > but task is already holding lock: > ffff9bbe88e4fc68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop] > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #4 (&lo->lo_mutex){+.+.}-{3:3}: > __mutex_lock+0x7d/0x750 > lo_open+0x28/0x60 [loop] > blkdev_get_whole+0x25/0xf0 > blkdev_get_by_dev.part.0+0x168/0x3c0 > blkdev_open+0xd2/0xe0 > do_dentry_open+0x161/0x390 > path_openat+0x3cc/0xa20 > do_filp_open+0x96/0x120 > do_sys_openat2+0x7b/0x130 > __x64_sys_openat+0x46/0x70 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > -> #3 (&disk->open_mutex){+.+.}-{3:3}: > __mutex_lock+0x7d/0x750 > blkdev_get_by_dev.part.0+0x56/0x3c0 > blkdev_get_by_path+0x98/0xa0 > btrfs_get_bdev_and_sb+0x1b/0xb0 > btrfs_find_device_by_devspec+0x12b/0x1c0 > btrfs_rm_device+0x127/0x610 > btrfs_ioctl+0x2a31/0x2e70 > __x64_sys_ioctl+0x80/0xb0 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > -> #2 (sb_writers#12){.+.+}-{0:0}: > lo_write_bvec+0xc2/0x240 [loop] > loop_process_work+0x238/0xd00 [loop] > process_one_work+0x26b/0x560 > worker_thread+0x55/0x3c0 > kthread+0x140/0x160 > ret_from_fork+0x1f/0x30 > > -> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}: > process_one_work+0x245/0x560 > worker_thread+0x55/0x3c0 > kthread+0x140/0x160 > ret_from_fork+0x1f/0x30 > > -> #0 ((wq_completion)loop0){+.+.}-{0:0}: > __lock_acquire+0x10ea/0x1d90 > lock_acquire+0xb5/0x2b0 > flush_workqueue+0x91/0x5e0 > drain_workqueue+0xa0/0x110 > destroy_workqueue+0x36/0x250 > __loop_clr_fd+0x9a/0x660 [loop] > block_ioctl+0x3f/0x50 > __x64_sys_ioctl+0x80/0xb0 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > other info that might help us debug this: > > Chain exists of: > (wq_completion)loop0 --> &disk->open_mutex --> &lo->lo_mutex > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&lo->lo_mutex); > lock(&disk->open_mutex); > lock(&lo->lo_mutex); > lock((wq_completion)loop0); > > *** DEADLOCK *** > > 1 lock held by losetup/11576: > #0: ffff9bbe88e4fc68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop] > > stack backtrace: > CPU: 0 PID: 11576 Comm: losetup Not tainted 5.14.0-rc2+ #405 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 > Call Trace: > dump_stack_lvl+0x57/0x72 > check_noncircular+0xcf/0xf0 > ? stack_trace_save+0x3b/0x50 > __lock_acquire+0x10ea/0x1d90 > lock_acquire+0xb5/0x2b0 > ? flush_workqueue+0x67/0x5e0 > ? lockdep_init_map_type+0x47/0x220 > flush_workqueue+0x91/0x5e0 > ? flush_workqueue+0x67/0x5e0 > ? verify_cpu+0xf0/0x100 > drain_workqueue+0xa0/0x110 > destroy_workqueue+0x36/0x250 > __loop_clr_fd+0x9a/0x660 [loop] > ? blkdev_ioctl+0x8d/0x2a0 > block_ioctl+0x3f/0x50 > __x64_sys_ioctl+0x80/0xb0 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > RIP: 0033:0x7f31b02404cb > > Signed-off-by: Josef Bacik > --- > fs/btrfs/volumes.c | 61 +++++++++++++++++----------------------------- > 1 file changed, 23 insertions(+), 38 deletions(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 0e7372f637eb..bf2449cdb2ab 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -2313,37 +2313,22 @@ void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev) > btrfs_free_device(tgtdev); > } > > -static struct btrfs_device *btrfs_find_device_by_path( > - struct btrfs_fs_info *fs_info, const char *device_path) > +static struct btrfs_device *find_device_by_path( > + struct btrfs_fs_devices *fs_devices, > + const char *path) > { > - int ret = 0; > - struct btrfs_super_block *disk_super; > - u64 devid; > - u8 *dev_uuid; > - struct block_device *bdev; > struct btrfs_device *device; > + bool missing = !strcmp(path, "missing"); > > - ret = btrfs_get_bdev_and_sb(device_path, FMODE_READ, > - fs_info->bdev_holder, 0, &bdev, &disk_super); > - if (ret) > - return ERR_PTR(ret); > - > - devid = btrfs_stack_device_id(&disk_super->dev_item); > - dev_uuid = disk_super->dev_item.uuid; > - if (btrfs_fs_incompat(fs_info, METADATA_UUID)) > - device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid, > - disk_super->metadata_uuid); > - else > - device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid, > - disk_super->fsid); > - > - btrfs_release_disk_super(disk_super); > - if (!device) > - device = ERR_PTR(-ENOENT); > - blkdev_put(bdev, FMODE_READ); > - return device; > + list_for_each_entry(device, &fs_devices->devices, dev_list) { > + if (missing && test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, > + &device->dev_state) && !device->bdev) > + return device; > + if (!missing && device_path_matched(path, device)) > + return device; > + } > + return NULL; > } > - > /* > * Lookup a device given by device id, or the path if the id is 0. > */ > @@ -2351,6 +2336,7 @@ struct btrfs_device *btrfs_find_device_by_devspec( > struct btrfs_fs_info *fs_info, u64 devid, > const char *device_path) > { > + struct btrfs_fs_devices *seed_devs; > struct btrfs_device *device; > > if (devid) { > @@ -2364,18 +2350,17 @@ struct btrfs_device *btrfs_find_device_by_devspec( > if (!device_path || !device_path[0]) > return ERR_PTR(-EINVAL); > > - if (strcmp(device_path, "missing") == 0) { > - /* Find first missing device */ > - list_for_each_entry(device, &fs_info->fs_devices->devices, > - dev_list) { > - if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, > - &device->dev_state) && !device->bdev) > - return device; > - } > - return ERR_PTR(-ENOENT); > - } > + device = find_device_by_path(fs_info->fs_devices, device_path); > + if (device) > + return device; > > - return btrfs_find_device_by_path(fs_info, device_path); > + list_for_each_entry(seed_devs, &fs_info->fs_devices->seed_list, > + seed_list) { > + device = find_device_by_path(seed_devs, device_path); > + if (device) > + return device; > + } > + return ERR_PTR(-ENOENT); > } > > /* >