[v5.15] possible deadlock in btrfs_start_transaction (2)

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syzbot

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Feb 2, 2025, 2:03:26 AM2/2/25

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Hello,

syzbot found the following issue on:

HEAD commit: c16c81c81336 Linux 5.15.178
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=11c98f24580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3ca28fba9b2e5c5
dashboard link: https://syzkaller.appspot.com/bug?extid=b56327bfdb9a4b46222a
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3f2947e5e4dc/disk-c16c81c8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7034800fdaa8/vmlinux-c16c81c8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/42337be7c213/Image-c16c81c8.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b56327...@syzkaller.appspotmail.com

BTRFS info (device loop6): enabling ssd optimizations
======================================================
WARNING: possible circular locking dependency detected
5.15.178-syzkaller #0 Not tainted
------------------------------------------------------
5�/5195 is trying to acquire lock:
ffff0000d7bf0650 (sb_internal#4){.+.+}-{0:0}, at: btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:777

but task is already holding lock:
ffff0000e925ad50 (&type->i_mutex_dir_key#10){++++}-{3:3}, at: inode_lock include/linux/fs.h:789 [inline]
ffff0000e925ad50 (&type->i_mutex_dir_key#10){++++}-{3:3}, at: vfs_fileattr_set+0x110/0xad4 fs/ioctl.c:685

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&type->i_mutex_dir_key#10){++++}-{3:3}:
down_read+0xc0/0x398 kernel/locking/rwsem.c:1498
inode_lock_shared include/linux/fs.h:799 [inline]
lookup_slow+0x50/0x84 fs/namei.c:1679
walk_component+0x394/0x4cc fs/namei.c:1976
lookup_last fs/namei.c:2431 [inline]
path_lookupat+0x13c/0x3d0 fs/namei.c:2455
filename_lookup+0x1c4/0x4c8 fs/namei.c:2484
kern_path+0x4c/0x194 fs/namei.c:2582
lookup_bdev+0xc0/0x25c block/bdev.c:979
device_matched fs/btrfs/volumes.c:568 [inline]
btrfs_free_stale_devices+0x658/0x9ec fs/btrfs/volumes.c:608
btrfs_forget_devices+0x5c/0x98 fs/btrfs/volumes.c:1431
btrfs_control_ioctl+0x12c/0x248 fs/btrfs/super.c:2451
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #1 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
__mutex_lock_common+0x194/0x2154 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0xa4/0xf8 kernel/locking/mutex.c:743
insert_dev_extents fs/btrfs/block-group.c:2395 [inline]
btrfs_create_pending_block_groups+0x490/0xebc fs/btrfs/block-group.c:2445
__btrfs_end_transaction+0x13c/0x610 fs/btrfs/transaction.c:1014
btrfs_end_transaction+0x24/0x34 fs/btrfs/transaction.c:1050
flush_space+0x458/0xc94 fs/btrfs/space-info.c:674
btrfs_async_reclaim_data_space+0xec/0x37c fs/btrfs/space-info.c:1169
process_one_work+0x790/0x11b8 kernel/workqueue.c:2310
worker_thread+0x910/0x1034 kernel/workqueue.c:2457
kthread+0x37c/0x45c kernel/kthread.c:334
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:870

-> #0 (sb_internal#4){.+.+}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1813 [inline]
sb_start_intwrite include/linux/fs.h:1930 [inline]
start_transaction+0x644/0x1480 fs/btrfs/transaction.c:678
btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:777
btrfs_fileattr_set+0x4dc/0x9b8 fs/btrfs/ioctl.c:331
vfs_fileattr_set+0x70c/0xad4 fs/ioctl.c:700
do_vfs_ioctl+0x1634/0x2a38
__do_sys_ioctl fs/ioctl.c:872 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0xe4/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

Chain exists of:
sb_internal#4 --> &fs_devs->device_list_mutex --> &type->i_mutex_dir_key#10

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&type->i_mutex_dir_key#10);
lock(&fs_devs->device_list_mutex);
lock(&type->i_mutex_dir_key#10);
lock(sb_internal#4);

*** DEADLOCK ***

2 locks held by 5�/5195:
#0: ffff0000d7bf0460 (sb_writers#14){.+.+}-{0:0}, at: mnt_want_write_file+0x64/0x1e8 fs/namespace.c:421
#1: ffff0000e925ad50 (&type->i_mutex_dir_key#10){++++}-{3:3}, at: inode_lock include/linux/fs.h:789 [inline]
#1: ffff0000e925ad50 (&type->i_mutex_dir_key#10){++++}-{3:3}, at: vfs_fileattr_set+0x110/0xad4 fs/ioctl.c:685

stack backtrace:
CPU: 1 PID: 5195 Comm: 5� Not tainted 5.15.178-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call trace:
dump_backtrace+0x0/0x530 arch/arm64/kernel/stacktrace.c:152
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
dump_stack+0x1c/0x58 lib/dump_stack.c:113
print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2011
check_noncircular+0x2cc/0x378 kernel/locking/lockdep.c:2133
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1813 [inline]
sb_start_intwrite include/linux/fs.h:1930 [inline]
start_transaction+0x644/0x1480 fs/btrfs/transaction.c:678
btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:777
btrfs_fileattr_set+0x4dc/0x9b8 fs/btrfs/ioctl.c:331
vfs_fileattr_set+0x70c/0xad4 fs/ioctl.c:700
do_vfs_ioctl+0x1634/0x2a38
__do_sys_ioctl fs/ioctl.c:872 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0xe4/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

---
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syzbot

unread,

Feb 2, 2025, 4:07:19 AM2/2/25

to syzkaller...@googlegroups.com

syzbot has found a reproducer for the following issue on:

HEAD commit: c16c81c81336 Linux 5.15.178
git tree: linux-5.15.y

console output: https://syzkaller.appspot.com/x/log.txt?x=16cbc764580000

kernel config: https://syzkaller.appspot.com/x/.config?x=3ca28fba9b2e5c5
dashboard link: https://syzkaller.appspot.com/bug?extid=b56327bfdb9a4b46222a
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=130c03df980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11dcad18580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3f2947e5e4dc/disk-c16c81c8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7034800fdaa8/vmlinux-c16c81c8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/42337be7c213/Image-c16c81c8.gz.xz

mounted in repro: https://storage.googleapis.com/syzbot-assets/54c03fc91d50/mount_1.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b56327...@syzkaller.appspotmail.com

BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)

======================================================
WARNING: possible circular locking dependency detected
5.15.178-syzkaller #0 Not tainted
------------------------------------------------------

syz-executor293/4019 is trying to acquire lock:
ffff0000c9d1a650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:777

but task is already holding lock:

ffff0000ddfd8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: inode_lock include/linux/fs.h:789 [inline]
ffff0000ddfd8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: vfs_fileattr_set+0x110/0xad4 fs/ioctl.c:685

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&type->i_mutex_dir_key#6){++++}-{3:3}:

down_read+0xc0/0x398 kernel/locking/rwsem.c:1498
inode_lock_shared include/linux/fs.h:799 [inline]
lookup_slow+0x50/0x84 fs/namei.c:1679
walk_component+0x394/0x4cc fs/namei.c:1976
lookup_last fs/namei.c:2431 [inline]
path_lookupat+0x13c/0x3d0 fs/namei.c:2455
filename_lookup+0x1c4/0x4c8 fs/namei.c:2484
kern_path+0x4c/0x194 fs/namei.c:2582
lookup_bdev+0xc0/0x25c block/bdev.c:979
device_matched fs/btrfs/volumes.c:568 [inline]
btrfs_free_stale_devices+0x658/0x9ec fs/btrfs/volumes.c:608
btrfs_forget_devices+0x5c/0x98 fs/btrfs/volumes.c:1431
btrfs_control_ioctl+0x12c/0x248 fs/btrfs/super.c:2451
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #2 (&fs_devs->device_list_mutex){+.+.}-{3:3}:

__mutex_lock_common+0x194/0x2154 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0xa4/0xf8 kernel/locking/mutex.c:743

btrfs_run_dev_stats+0xe4/0xe24 fs/btrfs/volumes.c:7985
commit_cowonly_roots+0x17c/0x808 fs/btrfs/transaction.c:1290
btrfs_commit_transaction+0xef4/0x30f0 fs/btrfs/transaction.c:2392
btrfs_clear_free_space_tree+0x5d0/0x9bc fs/btrfs/free-space-tree.c:1264
btrfs_start_pre_rw_mount+0x24c/0x578 fs/btrfs/disk-io.c:3079
open_ctree+0x2290/0x28f4 fs/btrfs/disk-io.c:3634
btrfs_fill_super+0x1b4/0x2c8 fs/btrfs/super.c:1387
btrfs_mount_root+0x6f8/0x7f8 fs/btrfs/super.c:1752
legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
vfs_get_tree+0x90/0x274 fs/super.c:1530
fc_mount fs/namespace.c:1000 [inline]
vfs_kern_mount+0xdc/0x178 fs/namespace.c:1030
btrfs_mount+0x328/0x9b8 fs/btrfs/super.c:1812
legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
vfs_get_tree+0x90/0x274 fs/super.c:1530
do_new_mount+0x278/0x8fc fs/namespace.c:3012
path_mount+0x594/0x101c fs/namespace.c:3342
do_mount fs/namespace.c:3355 [inline]
__do_sys_mount fs/namespace.c:3563 [inline]
__se_sys_mount fs/namespace.c:3540 [inline]
__arm64_sys_mount+0x510/0x5e0 fs/namespace.c:3540

__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #1 (&fs_info->tree_log_mutex){+.+.}-{3:3}:
__lock_release kernel/locking/lockdep.c:5339 [inline]
lock_release+0x340/0xa1c kernel/locking/lockdep.c:5643
__mutex_unlock_slowpath+0xe0/0x6d4 kernel/locking/mutex.c:851
mutex_unlock+0x8c/0xe0 kernel/locking/mutex.c:536
btrfs_commit_transaction+0x1650/0x30f0 fs/btrfs/transaction.c:2439
btrfs_clear_free_space_tree+0x5d0/0x9bc fs/btrfs/free-space-tree.c:1264
btrfs_start_pre_rw_mount+0x24c/0x578 fs/btrfs/disk-io.c:3079
open_ctree+0x2290/0x28f4 fs/btrfs/disk-io.c:3634
btrfs_fill_super+0x1b4/0x2c8 fs/btrfs/super.c:1387
btrfs_mount_root+0x6f8/0x7f8 fs/btrfs/super.c:1752
legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
vfs_get_tree+0x90/0x274 fs/super.c:1530
fc_mount fs/namespace.c:1000 [inline]
vfs_kern_mount+0xdc/0x178 fs/namespace.c:1030
btrfs_mount+0x328/0x9b8 fs/btrfs/super.c:1812
legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
vfs_get_tree+0x90/0x274 fs/super.c:1530
do_new_mount+0x278/0x8fc fs/namespace.c:3012
path_mount+0x594/0x101c fs/namespace.c:3342
do_mount fs/namespace.c:3355 [inline]
__do_sys_mount fs/namespace.c:3563 [inline]
__se_sys_mount fs/namespace.c:3540 [inline]
__arm64_sys_mount+0x510/0x5e0 fs/namespace.c:3540

-> #0 (sb_internal#2){.+.+}-{0:0}:

sb_internal#2 --> &fs_devs->device_list_mutex --> &type->i_mutex_dir_key#6

Possible unsafe locking scenario:

CPU0 CPU1
---- ----

lock(&type->i_mutex_dir_key#6);
lock(&fs_devs->device_list_mutex);
lock(&type->i_mutex_dir_key#6);
lock(sb_internal#2);

*** DEADLOCK ***

2 locks held by syz-executor293/4019:
#0: ffff0000c9d1a460 (sb_writers#8){.+.+}-{0:0}, at: mnt_want_write_file+0x64/0x1e8 fs/namespace.c:421
#1: ffff0000ddfd8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: inode_lock include/linux/fs.h:789 [inline]
#1: ffff0000ddfd8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: vfs_fileattr_set+0x110/0xad4 fs/ioctl.c:685

stack backtrace:
CPU: 0 PID: 4019 Comm: syz-executor293 Not tainted 5.15.178-syzkaller #0

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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