* [syzbot] [block?] possible deadlock in wbt_init_enable_default
@ 2026-10-31 23:30 syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-10-31 23:30 UTC (permalink / raw)
To: axboe, linux-block, linux-kernel, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: 151a134a4e6e Add linux-next specific files for 20261027
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16cfed21580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f530fbb08d65d27a
dashboard link: https://syzkaller.appspot.com/bug?extid=e2e1def00b1be94f0a22
compiler: Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c1d27f58c2b6/disk-151a134a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c2670074ce19/vmlinux-151a134a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1588f5d40496/bzImage-151a134a.xz
AI-generated root cause summary:
A race between disk registration in dm_setup_md_queue() and concurrent device
removal (dm_destroy() -> blk_mark_disk_dead()) causes the queue freeze lockdep
state tracking in block/blk-mq.c and block/blk.h to become inconsistent.
Although rq_qos_add() freezes and subsequently unfreezes the queue during
wbt_init_enable_default(), blk_unfreeze_release_lock() skips releasing
q->io_lockdep_map because the disk was concurrently marked dead/dying. When
wbt_init_enable_default() immediately proceeds to acquire q->debugfs_mutex,
lockdep detects an apparent circular locking dependency against the leaked
lockdep map. In production kernels without CONFIG_LOCKDEP, the queue is properly
unfrozen and no deadlock or memory corruption occurs.
full analysis: https://syzkaller.appspot.com/x/ai_root_cause?x=e2e1def00b1be94f0a22
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e2e1def00b1be94f0a22@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.2.182/6581 is trying to acquire lock:
ffff8880288865c8 (&q->debugfs_mutex){+.+.}-{4:4}, at: blk_debugfs_lock_nomemsave block/blk.h:800 [inline]
ffff8880288865c8 (&q->debugfs_mutex){+.+.}-{4:4}, at: blk_debugfs_lock block/blk.h:814 [inline]
ffff8880288865c8 (&q->debugfs_mutex){+.+.}-{4:4}, at: wbt_init_enable_default+0x146/0x220 block/blk-wbt.c:794
but task is already holding lock:
ffff888028885d80 (&q->q_usage_counter(io)#73){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:953 [inline]
ffff888028885d80 (&q->q_usage_counter(io)#73){++++}-{0:0}, at: rq_qos_add+0x15b/0x370 block/blk-rq-qos.c:341
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (&q->q_usage_counter(io)#73){++++}-{0:0}:
blk_alloc_queue+0x544/0x690 block/blk-core.c:505
__blk_alloc_disk+0xe3/0x1d0 block/genhd.c:1527
alloc_dev drivers/md/dm.c:2349 [inline]
dm_create+0x476/0xf70 drivers/md/dm.c:2563
dev_create+0x1f7/0x400 drivers/md/dm-ioctl.c:977
ctl_ioctl drivers/md/dm-ioctl.c:2221 [inline]
dm_ctl_ioctl+0x9ec/0xe10 drivers/md/dm-ioctl.c:2243
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire mm/page_alloc.c:4363 [inline]
fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4377
might_alloc include/linux/sched/mm.h:316 [inline]
slab_pre_alloc_hook mm/slub.c:4673 [inline]
slab_alloc_node mm/slub.c:5011 [inline]
kmem_cache_alloc_lru_noprof+0x65/0x5f0 mm/slub.c:5066
__d_alloc+0x37/0x820 fs/dcache.c:1924
d_alloc+0x4b/0x190 fs/dcache.c:2010
lookup_one_qstr_excl+0xd8/0x360 fs/namei.c:1806
__start_dirop fs/namei.c:2920 [inline]
start_dirop+0x5c/0x90 fs/namei.c:2942
simple_start_creating+0xcc/0x110 fs/libfs.c:2308
debugfs_start_creating+0xca/0x1b0 fs/debugfs/inode.c:397
debugfs_create_dir+0x24/0x350 fs/debugfs/inode.c:575
regulator_init+0x6c/0x110 drivers/regulator/core.c:6787
do_one_initcall+0x250/0x870 init/main.c:1419
do_initcall_level+0x10a/0x1a0 init/main.c:1481
do_initcalls+0x59/0xa0 init/main.c:1497
kernel_init_freeable+0x29d/0x3e0 init/main.c:1732
kernel_init+0x22/0x1d0 init/main.c:1622
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #1 (&sb->s_type->i_mutex_key#3/1){+.+.}-{4:4}:
down_write_nested+0x98/0x200 kernel/locking/rwsem.c:1757
inode_lock_nested include/linux/fs.h:1069 [inline]
__start_dirop fs/namei.c:2918 [inline]
start_dirop+0x4f/0x90 fs/namei.c:2942
simple_start_creating+0xcc/0x110 fs/libfs.c:2308
debugfs_start_creating+0xca/0x1b0 fs/debugfs/inode.c:397
debugfs_create_dir+0x24/0x350 fs/debugfs/inode.c:575
blk_register_queue+0x189/0x4f0 block/blk-sysfs.c:968
__add_disk+0x6b8/0xdb0 block/genhd.c:531
add_disk_fwnode+0x143/0x3a0 block/genhd.c:604
add_disk include/linux/blkdev.h:801 [inline]
brd_alloc+0x5a9/0x7c0 drivers/block/brd.c:340
brd_init+0xc1/0x120 drivers/block/brd.c:420
do_one_initcall+0x250/0x870 init/main.c:1419
do_initcall_level+0x10a/0x1a0 init/main.c:1481
do_initcalls+0x59/0xa0 init/main.c:1497
kernel_init_freeable+0x29d/0x3e0 init/main.c:1732
kernel_init+0x22/0x1d0 init/main.c:1622
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #0 (&q->debugfs_mutex){+.+.}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
blk_debugfs_lock_nomemsave block/blk.h:800 [inline]
blk_debugfs_lock block/blk.h:814 [inline]
wbt_init_enable_default+0x146/0x220 block/blk-wbt.c:794
blk_register_queue+0x420/0x4f0 block/blk-sysfs.c:995
__add_disk+0x6b8/0xdb0 block/genhd.c:531
add_disk_fwnode+0x100/0x3a0 block/genhd.c:600
add_disk include/linux/blkdev.h:801 [inline]
dm_setup_md_queue+0x23d/0x4f0 drivers/md/dm.c:2632
table_load+0x4fd/0x8a0 drivers/md/dm-ioctl.c:1661
ctl_ioctl drivers/md/dm-ioctl.c:2221 [inline]
dm_ctl_ioctl+0x9ec/0xe10 drivers/md/dm-ioctl.c:2243
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
&q->debugfs_mutex --> fs_reclaim --> &q->q_usage_counter(io)#73
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&q->q_usage_counter(io)#73);
lock(fs_reclaim);
lock(&q->q_usage_counter(io)#73);
lock(&q->debugfs_mutex);
*** DEADLOCK ***
locks held by syz.2.182/6581: 6, last CPU#0:
#0: ffff88807ce11190 (&md->type_lock){+.+.}-{4:4}, at: table_load+0x1dd/0x8a0 drivers/md/dm-ioctl.c:1644
#1: ffff88807ce110e8 (&md->table_devices_lock){+.+.}-{4:4}, at: dm_setup_md_queue+0x20b/0x4f0 drivers/md/dm.c:2631
#2: ffff888035d3ad78 (&set->update_nr_hwq_lock){.+.+}-{4:4}, at: add_disk_fwnode+0xea/0x3a0 block/genhd.c:599
#3: ffff888028886330 (&q->sysfs_lock){+.+.}-{4:4}, at: blk_register_queue+0x10d/0x4f0 block/blk-sysfs.c:965
#4: ffff888028885d80 (&q->q_usage_counter(io)#73){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:953 [inline]
#4: ffff888028885d80 (&q->q_usage_counter(io)#73){++++}-{0:0}, at: rq_qos_add+0x15b/0x370 block/blk-rq-qos.c:341
#5: ffff888028885db8 (&q->q_usage_counter(queue)#54){+.+.}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:953 [inline]
#5: ffff888028885db8 (&q->q_usage_counter(queue)#54){+.+.}-{0:0}, at: rq_qos_add+0x15b/0x370 block/blk-rq-qos.c:341
stack backtrace:
CPU: 0 UID: 0 PID: 6581 Comm: syz.2.182 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
blk_debugfs_lock_nomemsave block/blk.h:800 [inline]
blk_debugfs_lock block/blk.h:814 [inline]
wbt_init_enable_default+0x146/0x220 block/blk-wbt.c:794
blk_register_queue+0x420/0x4f0 block/blk-sysfs.c:995
__add_disk+0x6b8/0xdb0 block/genhd.c:531
add_disk_fwnode+0x100/0x3a0 block/genhd.c:600
add_disk include/linux/blkdev.h:801 [inline]
dm_setup_md_queue+0x23d/0x4f0 drivers/md/dm.c:2632
table_load+0x4fd/0x8a0 drivers/md/dm-ioctl.c:1661
ctl_ioctl drivers/md/dm-ioctl.c:2221 [inline]
dm_ctl_ioctl+0x9ec/0xe10 drivers/md/dm-ioctl.c:2243
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f876af9f559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f876be1d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f876b225fa0 RCX: 00007f876af9f559
RDX: 0000200000000380 RSI: 00000000c138fd09 RDI: 0000000000000004
RBP: 00007f876b036b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f876b226038 R14: 00007f876b225fa0 R15: 00007ffe8962be28
</TASK>
device-mapper: ioctl: device has been removed from the dev hash table.
---
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2026-10-31 23:30 [syzbot] [block?] possible deadlock in wbt_init_enable_default syzbot
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