[v5.15] possible deadlock in btrfs_join_transaction

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Jan 20, 2024, 4:24:19 PMJan 20
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Hello,

syzbot found the following issue on:

HEAD commit: ddcaf4999061 Linux 5.15.147
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14cda91be80000
kernel config: https://syzkaller.appspot.com/x/.config?x=ab92786ed9f7c373
dashboard link: https://syzkaller.appspot.com/bug?extid=41d447453faf9e956c83
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/9f538e3b5b6b/disk-ddcaf499.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aff958e6c838/vmlinux-ddcaf499.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b812c40b66fa/Image-ddcaf499.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+41d447...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.15.147-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.3/32659 is trying to acquire lock:
ffff0000dcf74650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:791

but task is already holding lock:
ffff000126f24058 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff000126f24058 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x15c/0x2b4 mm/util.c:549

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&mm->mmap_lock){++++}-{3:3}:
__might_fault+0xc8/0x128 mm/memory.c:5324
filldir64+0x2bc/0x9e4 fs/readdir.c:335
dir_emit_dot include/linux/fs.h:3650 [inline]
dir_emit_dots include/linux/fs.h:3661 [inline]
dcache_readdir+0x134/0x678 fs/libfs.c:196
iterate_dir+0x1f4/0x4e4
__do_sys_getdents64 fs/readdir.c:369 [inline]
__se_sys_getdents64 fs/readdir.c:354 [inline]
__arm64_sys_getdents64+0x1c4/0x4c4 fs/readdir.c:354
__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

-> #3 (&type->i_mutex_dir_key#2){++++}-{3:3}:
down_read+0xc0/0x398 kernel/locking/rwsem.c:1488
inode_lock_shared include/linux/fs.h:797 [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:563 [inline]
btrfs_free_stale_devices+0x61c/0x9ec fs/btrfs/volumes.c:608
btrfs_scan_one_device+0x438/0x5f8 fs/btrfs/volumes.c:1448
btrfs_mount_root+0x424/0x7f8 fs/btrfs/super.c:1716
legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
vfs_get_tree+0x90/0x274 fs/super.c:1517
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:1517
do_new_mount+0x25c/0x8c4 fs/namespace.c:2994
path_mount+0x594/0x101c fs/namespace.c:3324
do_mount fs/namespace.c:3337 [inline]
__do_sys_mount fs/namespace.c:3545 [inline]
__se_sys_mount fs/namespace.c:3522 [inline]
__arm64_sys_mount+0x510/0x5e0 fs/namespace.c:3522
__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:7931
commit_cowonly_roots+0x17c/0x808 fs/btrfs/transaction.c:1290
btrfs_commit_transaction+0xef4/0x30f0 fs/btrfs/transaction.c:2392
btrfs_sync_fs+0x678/0xc94 fs/btrfs/super.c:1454
sync_filesystem+0x1a0/0x218 fs/sync.c:66
generic_shutdown_super+0x70/0x29c fs/super.c:448
kill_anon_super+0x4c/0x74 fs/super.c:1076
btrfs_kill_super+0x40/0x58 fs/btrfs/super.c:2391
deactivate_locked_super+0xb8/0x13c fs/super.c:335
deactivate_super+0x108/0x128 fs/super.c:366
cleanup_mnt+0x3c0/0x474 fs/namespace.c:1143
__cleanup_mnt+0x20/0x30 fs/namespace.c:1150
task_work_run+0x130/0x1e4 kernel/task_work.c:164
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
do_notify_resume+0x262c/0x32b8 arch/arm64/kernel/signal.c:946
prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:133 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:138 [inline]
el0_svc+0xfc/0x1f0 arch/arm64/kernel/entry-common.c:609
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_commit_super+0xb4/0xd0 fs/btrfs/disk-io.c:4326
close_ctree+0x378/0x860 fs/btrfs/disk-io.c:4438
btrfs_put_super+0x40/0x50 fs/btrfs/super.c:340
generic_shutdown_super+0x130/0x29c fs/super.c:475
kill_anon_super+0x4c/0x74 fs/super.c:1076
btrfs_kill_super+0x40/0x58 fs/btrfs/super.c:2391
deactivate_locked_super+0xb8/0x13c fs/super.c:335
deactivate_super+0x108/0x128 fs/super.c:366
cleanup_mnt+0x3c0/0x474 fs/namespace.c:1143
__cleanup_mnt+0x20/0x30 fs/namespace.c:1150
task_work_run+0x130/0x1e4 kernel/task_work.c:164
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
do_notify_resume+0x262c/0x32b8 arch/arm64/kernel/signal.c:946
prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:133 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:138 [inline]
el0_svc+0xfc/0x1f0 arch/arm64/kernel/entry-common.c:609
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #0 (sb_internal#2){.+.+}-{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:1785 [inline]
sb_start_intwrite include/linux/fs.h:1902 [inline]
start_transaction+0x644/0x1480 fs/btrfs/transaction.c:678
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:791
btrfs_dirty_inode+0xb4/0x1c0 fs/btrfs/inode.c:6329
btrfs_update_time+0x248/0x270 fs/btrfs/inode.c:6371
inode_update_time fs/inode.c:1829 [inline]
touch_atime+0x434/0xa4c fs/inode.c:1902
file_accessed include/linux/fs.h:2490 [inline]
btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2424
call_mmap include/linux/fs.h:2151 [inline]
mmap_region+0xcb4/0x12f0 mm/mmap.c:1791
do_mmap+0x6c0/0xcec mm/mmap.c:1575
vm_mmap_pgoff+0x1a4/0x2b4 mm/util.c:551
ksys_mmap_pgoff+0x458/0x668 mm/mmap.c:1624
__do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
__se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
__arm64_sys_mmap+0xf8/0x110 arch/arm64/kernel/sys.c:21
__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#2 --> &type->i_mutex_dir_key#2 --> &mm->mmap_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&mm->mmap_lock);
lock(&type->i_mutex_dir_key#2);
lock(&mm->mmap_lock);
lock(sb_internal#2);

*** DEADLOCK ***

2 locks held by syz-executor.3/32659:
#0: ffff000126f24058 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
#0: ffff000126f24058 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x15c/0x2b4 mm/util.c:549
#1: ffff0000dcf74460 (sb_writers#16){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2490 [inline]
#1: ffff0000dcf74460 (sb_writers#16){.+.+}-{0:0}, at: btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2424

stack backtrace:
CPU: 0 PID: 32659 Comm: syz-executor.3 Not tainted 5.15.147-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
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:1785 [inline]
sb_start_intwrite include/linux/fs.h:1902 [inline]
start_transaction+0x644/0x1480 fs/btrfs/transaction.c:678
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:791
btrfs_dirty_inode+0xb4/0x1c0 fs/btrfs/inode.c:6329
btrfs_update_time+0x248/0x270 fs/btrfs/inode.c:6371
inode_update_time fs/inode.c:1829 [inline]
touch_atime+0x434/0xa4c fs/inode.c:1902
file_accessed include/linux/fs.h:2490 [inline]
btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2424
call_mmap include/linux/fs.h:2151 [inline]
mmap_region+0xcb4/0x12f0 mm/mmap.c:1791
do_mmap+0x6c0/0xcec mm/mmap.c:1575
vm_mmap_pgoff+0x1a4/0x2b4 mm/util.c:551
ksys_mmap_pgoff+0x458/0x668 mm/mmap.c:1624
__do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
__se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
__arm64_sys_mmap+0xf8/0x110 arch/arm64/kernel/sys.c:21
__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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