On Fri 26 Feb 2021 at 13:01, Anand Jain <anand.j...@oracle.com> wrote:

On 25/02/2021 12:39, Su Yue wrote:
While playing with seed device(misc/next and v5.11), lockdep complains
the following:
To reproduce:
dev1=/dev/sdb1
dev2=/dev/sdb2
umount /mnt
mkfs.btrfs -f $dev1
btrfstune -S 1 $dev1
mount $dev1 /mnt
btrfs device add $dev2 /mnt/ -f
umount /mnt
mount $dev2 /mnt
umount /mnt


In my understanding the commit 01d01caf19ff7c537527d352d169c4368375c0a1
 (btrfs: move the chunk_mutex in btrfs_read_chunk_tree
 fixed this bug in 5.9.
Could you please try this [1] patch,
[1]
https://patchwork.kernel.org/project/linux-btrfs/patch/20200717100525.320697-1-anand.j...@oracle.com/
Patch [1] still relevant as the device_list_mutex in clone_fs_devices() is
redundant. We could remove it as well.

Thanks for taking a look first.  Obviously,  the patch silences the
current warning after removing the device_list_mutex even lockdep
warnings differ.
I'm too foolish to read seed device freeing code so I'd say your patch
works.

Thanks,
Su

Thanks, Anand

Warning:
[ 104.348749] BTRFS: device fsid 9a34d68b-fd18-470c-8cfc-44916c364c76
devid 1 transid 5 /dev/sdb1 scanned by mkfs.btrfs (627)
[ 104.377243] BTRFS info (device sdb1): disk space caching is enabled
[  104.378091] BTRFS info (device sdb1): has skinny extents
[ 104.378800] BTRFS info (device sdb1): flagging fs with big metadata feature [ 104.512522] BTRFS info (device sdb1): relocating block group 567279616
flags system|dup
[ 104.535912] BTRFS info (device sdb1): relocating block group 22020096 flags
system|dup
[  104.571307] BTRFS info (device sdb1): disk added /dev/sdb2
[ 104.602831] BTRFS info (device sdb2): disk space caching is enabled
[  104.603692] BTRFS info (device sdb2): has skinny extents
[ 104.606389] ====================================================== [ 104.607212] WARNING: possible circular locking dependency detected
[  104.608025] 5.11.0-rc7-custom+ #55 Tainted: G           O
[ 104.608790] ------------------------------------------------------
[  104.609599] mount/670 is trying to acquire lock:
[ 104.610207] ffffa2274d7158e8 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at:
clone_fs_devices+0x4f/0x160 [btrfs]
[  104.611585]
               but task is already holding lock:
[ 104.612334] ffffa22750e32f20 (btrfs-chunk-00){++++}-{3:3}, at:
__btrfs_tree_read_lock+0x2d/0x110 [btrfs]
[  104.651264]
               which lock already depends on the new lock.
[  104.708041]
               the existing dependency chain (in reverse order)
is:
[  104.743619]
               -> #1 (btrfs-chunk-00){++++}-{3:3}:
[  104.777693]        down_read_nested+0x4b/0x140
[  104.794386]        __btrfs_tree_read_lock+0x2d/0x110 [btrfs]
[ 104.811338] btrfs_read_lock_root_node+0x36/0x50 [btrfs]
[  104.828574]        btrfs_search_slot+0x473/0x900 [btrfs]
[  104.845543]        btrfs_update_device+0x71/0x1a0 [btrfs]
[ 104.862164] btrfs_finish_chunk_alloc+0x121/0x490 [btrfs] [ 104.878474] btrfs_create_pending_block_groups+0x151/0x2c0 [btrfs] [ 104.894725] btrfs_commit_transaction+0x82/0xb30 [btrfs] [ 104.910808] btrfs_init_new_device+0x1015/0x14d0 [btrfs]
[  104.926879]        btrfs_ioctl+0x1ff/0x2fc0 [btrfs]
[  104.942996]        __x64_sys_ioctl+0x91/0xc0
[  104.958874]        do_syscall_64+0x38/0x50
[  104.974554]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  104.990108]
               -> #0 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
[  105.020508]        __lock_acquire+0x11e0/0x1ea0
[  105.035759]        lock_acquire+0xd8/0x3c0
[  105.050434]        __mutex_lock+0x8f/0x870
[  105.064614]        mutex_lock_nested+0x1b/0x20
[  105.078641]        clone_fs_devices+0x4f/0x160 [btrfs]
[  105.092984]        btrfs_read_chunk_tree+0x30e/0x7f0 [btrfs]
[  105.107031]        open_ctree+0xb40/0x176a [btrfs]
[  105.120673]        btrfs_mount_root.cold+0x12/0xeb [btrfs]
[  105.134564]        legacy_get_tree+0x34/0x60
[  105.148347]        vfs_get_tree+0x2d/0xc0
[  105.162053]        vfs_kern_mount.part.0+0x78/0xc0
[  105.176072]        vfs_kern_mount+0x13/0x20
[  105.189844]        btrfs_mount+0x11f/0x3c0 [btrfs]
[  105.203396]        legacy_get_tree+0x34/0x60
[  105.217129]        vfs_get_tree+0x2d/0xc0
[  105.230536]        path_mount+0x48c/0xd30
[  105.243915]        __x64_sys_mount+0x108/0x140
[  105.257030]        do_syscall_64+0x38/0x50
[  105.270084]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  105.283382]
               other info that might help us debug this:
[  105.321699]  Possible unsafe locking scenario:
[  105.347053]        CPU0                    CPU1
[  105.359640]        ----                    ----
[  105.372004]   lock(btrfs-chunk-00);
[  105.384023] lock(&fs_devs->device_list_mutex);
[  105.396858] lock(btrfs-chunk-00);
[  105.409215]   lock(&fs_devs->device_list_mutex);
[  105.421625]
                *** DEADLOCK ***
[  105.457447] 3 locks held by mount/670:
[ 105.469302] #0: ffffa2270932e0e8 (&type->s_umount_key#54/1){+.+.}-{3:3},
at: alloc_super+0xdf/0x3c0
[ 105.494413] #1: ffffffffc0bdfdd0 (uuid_mutex){+.+.}-{3:3}, at:
btrfs_read_chunk_tree+0x5c/0x7f0 [btrfs]
[ 105.521072] #2: ffffa22750e32f20 (btrfs-chunk-00){++++}-{3:3}, at:
__btrfs_tree_read_lock+0x2d/0x110 [btrfs]
[  105.549753]
               stack backtrace:
[ 105.578187] CPU: 6 PID: 670 Comm: mount Tainted: G O
5.11.0-rc7-custom+ #55
[ 105.607477] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
ArchLinux 1.14.0-1 04/01/2014
[  105.638608] Call Trace:
[  105.653967]  dump_stack+0x90/0xb8
[  105.669419]  print_circular_bug.cold+0x13d/0x142
[  105.684814]  check_noncircular+0xf2/0x110
[  105.700322]  ? check_path.constprop.0+0x26/0x40
[  105.715821]  __lock_acquire+0x11e0/0x1ea0
[  105.731388]  ? __this_cpu_preempt_check+0x13/0x20
[  105.747097]  ? lockdep_unlock+0x33/0xd0
[  105.763012]  lock_acquire+0xd8/0x3c0
[  105.779043]  ? clone_fs_devices+0x4f/0x160 [btrfs]
[  105.795343]  __mutex_lock+0x8f/0x870
[  105.811251]  ? clone_fs_devices+0x4f/0x160 [btrfs]
[  105.827385]  ? lockdep_init_map_waits+0x51/0x250
[  105.843343]  ? clone_fs_devices+0x4f/0x160 [btrfs]
[  105.859264]  ? debug_mutex_init+0x36/0x50
[  105.875378]  ? __mutex_init+0x62/0x70
[  105.891493]  mutex_lock_nested+0x1b/0x20
[  105.907847]  clone_fs_devices+0x4f/0x160 [btrfs]
[  105.923756]  ? btrfs_get_64+0x63/0x110 [btrfs]
[  105.939389]  btrfs_read_chunk_tree+0x30e/0x7f0 [btrfs]
[  105.954580]  open_ctree+0xb40/0x176a [btrfs]
[  105.969477]  ? bdi_register_va+0x1b/0x20
[  105.983674]  ? super_setup_bdi_name+0x79/0xd0
[  105.997611]  btrfs_mount_root.cold+0x12/0xeb [btrfs]
[  106.011564]  ? __kmalloc_track_caller+0x217/0x3b0
[  106.026013]  legacy_get_tree+0x34/0x60
[  106.040045]  vfs_get_tree+0x2d/0xc0
[  106.053904]  vfs_kern_mount.part.0+0x78/0xc0
[  106.067296]  vfs_kern_mount+0x13/0x20
[  106.080125]  btrfs_mount+0x11f/0x3c0 [btrfs]
[  106.093144]  ? kfree+0x5ff/0x670
[  106.106064]  ? __kmalloc_track_caller+0x217/0x3b0
[  106.119249]  legacy_get_tree+0x34/0x60
[  106.132216]  vfs_get_tree+0x2d/0xc0
[  106.145225]  path_mount+0x48c/0xd30
[  106.157899]  __x64_sys_mount+0x108/0x140
[  106.170654]  do_syscall_64+0x38/0x50
[  106.183208]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  106.196111] RIP: 0033:0x7fafa8869ebe
[ 106.208994] Code: 48 8b 0d b5 0f 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d
01 f0 ff ff 73 01 c3 48 8b 0d 82 0f 0c 00 f7 d8 64 89 01 48
[ 106.250073] RSP: 002b:00007ffc04365b98 EFLAGS: 00000246 ORIG_RAX:
00000000000000a5
[  106.278571] RAX: ffffffffffffffda RBX: 00007fafa8994264 RCX:
00007fafa8869ebe
[  106.294048] RDX: 0000556726a02e00 RSI: 00005567269fc690 RDI:
00005567269fc670
[  106.309646] RBP: 00005567269fc440 R08: 0000000000000000 R09:
00007fafa892ba60
[  106.325336] R10: 0000000000000000 R11: 0000000000000246 R12:
0000000000000000
[  106.340847] R13: 00005567269fc670 R14: 0000556726a02e00 R15:
00005567269fc440
[  106.357929] BTRFS info (device sdb2): checking UUID tree

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