[syzbot] [block?] possible deadlock in __del_gendisk

[syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    3be1a7a31fbd Add linux-next specific files for 20250526
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1573bad4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9ab703e8a19430df
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/33e6b012d232/disk-3be1a7a3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f92328298470/vmlinux-3be1a7a3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e5cbdb6f4a5c/bzImage-3be1a7a3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2e9e529ac0b319316453@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.15.0-rc7-next-20250526-syzkaller #0 Not tainted
------------------------------------------------------
syz.4.1558/11720 is trying to acquire lock:
ffff888142bb3358 (&disk->open_mutex){+.+.}-{4:4}, at: __del_gendisk+0x129/0x9e0 block/genhd.c:706

but task is already holding lock:
ffff888142bb2368 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&set->update_nr_hwq_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
       blk_mq_update_nr_hw_queues+0x3b/0x14c0 block/blk-mq.c:5041
       nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
       nbd_genl_connect+0x1250/0x1930 drivers/block/nbd.c:2201
       genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2534
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
       netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
       sock_sendmsg_nosec net/socket.c:712 [inline]
       __sock_sendmsg+0x21c/0x270 net/socket.c:727
       ____sys_sendmsg+0x505/0x830 net/socket.c:2566
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
       __sys_sendmsg net/socket.c:2652 [inline]
       __do_sys_sendmsg net/socket.c:2657 [inline]
       __se_sys_sendmsg net/socket.c:2655 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&nbd->config_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118
       nbd_config_put+0x2c/0x790 drivers/block/nbd.c:1423
       nbd_release+0xfe/0x140 drivers/block/nbd.c:1735
       bdev_release+0x536/0x650 block/bdev.c:-1
       blkdev_release+0x15/0x20 block/fops.c:684
       __fput+0x44c/0xa70 fs/file_table.c:467
       fput_close_sync+0x119/0x200 fs/file_table.c:572
       __do_sys_close fs/open.c:1589 [inline]
       __se_sys_close fs/open.c:1574 [inline]
       __x64_sys_close+0x7f/0x110 fs/open.c:1574
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&disk->open_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       __del_gendisk+0x129/0x9e0 block/genhd.c:706
       del_gendisk+0xe8/0x160 block/genhd.c:819
       loop_remove+0x42/0xc0 drivers/block/loop.c:2081
       loop_control_remove drivers/block/loop.c:2140 [inline]
       loop_control_ioctl+0x4a6/0x590 drivers/block/loop.c:2178
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &disk->open_mutex --> &nbd->config_lock --> &set->update_nr_hwq_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&set->update_nr_hwq_lock);
                               lock(&nbd->config_lock);
                               lock(&set->update_nr_hwq_lock);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

1 lock held by syz.4.1558/11720:
 #0: ffff888142bb2368 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

stack backtrace:
CPU: 0 UID: 0 PID: 11720 Comm: syz.4.1558 Not tainted 6.15.0-rc7-next-20250526-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
 __del_gendisk+0x129/0x9e0 block/genhd.c:706
 del_gendisk+0xe8/0x160 block/genhd.c:819
 loop_remove+0x42/0xc0 drivers/block/loop.c:2081
 loop_control_remove drivers/block/loop.c:2140 [inline]
 loop_control_ioctl+0x4a6/0x590 drivers/block/loop.c:2178
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f301358e969
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f30113f6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f30137b5fa0 RCX: 00007f301358e969
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 0000000000000003
RBP: 00007f3013610ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f30137b5fa0 R15: 00007fffe9613fd8
 </TASK>


---
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If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    ddddf9d64f73 Merge tag 'perf-core-2025-05-25' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12f87882580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fd18a1001092f95b
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11825df4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17fb7ad4580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-ddddf9d6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bc551d1d4e46/vmlinux-ddddf9d6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d26a6de23b0e/bzImage-ddddf9d6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2e9e529ac0b319316453@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.15.0-syzkaller-01599-gddddf9d64f73 #0 Not tainted
------------------------------------------------------
kworker/u4:9/1091 is trying to acquire lock:
ffff888011362358 (&disk->open_mutex){+.+.}-{4:4}, at: __del_gendisk+0x129/0x9e0 block/genhd.c:706

but task is already holding lock:
ffff88801bb55188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&set->update_nr_hwq_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
       blk_mq_update_nr_hw_queues+0x3b/0x14c0 block/blk-mq.c:5041
       nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
       nbd_genl_connect+0x1250/0x1930 drivers/block/nbd.c:2201
       genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x219/0x490 net/netlink/af_netlink.c:2534
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
       netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
       sock_sendmsg_nosec net/socket.c:712 [inline]
       __sock_sendmsg+0x219/0x270 net/socket.c:727
       ____sys_sendmsg+0x505/0x830 net/socket.c:2566
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
       __sys_sendmsg net/socket.c:2652 [inline]
       __do_sys_sendmsg net/socket.c:2657 [inline]
       __se_sys_sendmsg net/socket.c:2655 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&nbd->config_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118
       nbd_config_put+0x2c/0x790 drivers/block/nbd.c:1423
       nbd_release+0xfe/0x140 drivers/block/nbd.c:1735
       bdev_release+0x533/0x650 block/bdev.c:-1
       blkdev_release+0x15/0x20 block/fops.c:684
       __fput+0x449/0xa70 fs/file_table.c:465
       fput_close_sync+0x119/0x200 fs/file_table.c:570
       __do_sys_close fs/open.c:1589 [inline]
       __se_sys_close fs/open.c:1574 [inline]
       __x64_sys_close+0x7f/0x110 fs/open.c:1574
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&disk->open_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       __del_gendisk+0x129/0x9e0 block/genhd.c:706
       del_gendisk+0xe8/0x160 block/genhd.c:819
       nbd_dev_remove drivers/block/nbd.c:268 [inline]
       nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
       process_one_work kernel/workqueue.c:3238 [inline]
       process_scheduled_works+0xadb/0x17a0 kernel/workqueue.c:3319
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
       kthread+0x711/0x8a0 kernel/kthread.c:464
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  &disk->open_mutex --> &nbd->config_lock --> &set->update_nr_hwq_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&set->update_nr_hwq_lock);
                               lock(&nbd->config_lock);
                               lock(&set->update_nr_hwq_lock);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

3 locks held by kworker/u4:9/1091:
 #0: ffff88801f317148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3213 [inline]
 #0: ffff88801f317148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_scheduled_works+0x9b1/0x17a0 kernel/workqueue.c:3319
 #1: ffffc90002647c60 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3214 [inline]
 #1: ffffc90002647c60 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ec/0x17a0 kernel/workqueue.c:3319
 #2: ffff88801bb55188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

stack backtrace:
CPU: 0 UID: 0 PID: 1091 Comm: kworker/u4:9 Not tainted 6.15.0-syzkaller-01599-gddddf9d64f73 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: nbd-del nbd_dev_remove_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:601 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
 __del_gendisk+0x129/0x9e0 block/genhd.c:706
 del_gendisk+0xe8/0x160 block/genhd.c:819
 nbd_dev_remove drivers/block/nbd.c:268 [inline]
 nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xadb/0x17a0 kernel/workqueue.c:3319
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


---
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.

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in __del_gendisk

======================================================
WARNING: possible circular locking dependency detected
6.15.0-syzkaller-g914873bc7df9-dirty #0 Not tainted
------------------------------------------------------
kworker/u4:1/13 is trying to acquire lock:
ffff888059e20358 (&disk->open_mutex){+.+.}-{4:4}, at: __del_gendisk+0x129/0x9e0 block/genhd.c:706

but task is already holding lock:
ffff888053877188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&set->update_nr_hwq_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
       blk_mq_update_nr_hw_queues+0x3b/0x14c0 block/blk-mq.c:5041
       nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
       nbd_genl_connect+0x1250/0x1930 drivers/block/nbd.c:2201
       genl_family_rcv_msg_doit+0x212/0x300 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x21c/0x490 net/netlink/af_netlink.c:2534
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
       netlink_unicast+0x758/0x8d0 net/netlink/af_netlink.c:1339
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
       sock_sendmsg_nosec net/socket.c:712 [inline]
       __sock_sendmsg+0x21c/0x270 net/socket.c:727
       ____sys_sendmsg+0x505/0x830 net/socket.c:2566
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
       __sys_sendmsg net/socket.c:2652 [inline]
       __do_sys_sendmsg net/socket.c:2657 [inline]
       __se_sys_sendmsg net/socket.c:2655 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x220 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&nbd->config_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       nbd_open+0x2b7/0x5d0 drivers/block/nbd.c:1703
       blkdev_get_whole+0x98/0x510 block/bdev.c:730
       bdev_open+0x31e/0xd30 block/bdev.c:957
       blkdev_open+0x3a8/0x510 block/fops.c:676
       do_dentry_open+0xdf3/0x1970 fs/open.c:964
       vfs_open+0x3b/0x340 fs/open.c:1094
       do_open fs/namei.c:3887 [inline]
       path_openat+0x2ee5/0x3830 fs/namei.c:4046
       do_filp_open+0x1fa/0x410 fs/namei.c:4073
       do_sys_openat2+0x121/0x1c0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x220 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (nbd_index_mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       nbd_open+0x7b/0x5d0 drivers/block/nbd.c:1690
       blkdev_get_whole+0x98/0x510 block/bdev.c:730
       bdev_open+0x31e/0xd30 block/bdev.c:957
       blkdev_open+0x3a8/0x510 block/fops.c:676
       do_dentry_open+0xdf3/0x1970 fs/open.c:964
       vfs_open+0x3b/0x340 fs/open.c:1094
       do_open fs/namei.c:3887 [inline]
       path_openat+0x2ee5/0x3830 fs/namei.c:4046
       do_filp_open+0x1fa/0x410 fs/namei.c:4073
       do_sys_openat2+0x121/0x1c0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x220 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&disk->open_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       __del_gendisk+0x129/0x9e0 block/genhd.c:706
       del_gendisk+0xe8/0x160 block/genhd.c:819
       nbd_dev_remove drivers/block/nbd.c:268 [inline]
       nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
       process_one_work kernel/workqueue.c:3238 [inline]
       process_scheduled_works+0xade/0x17a0 kernel/workqueue.c:3319
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
       kthread+0x70e/0x8a0 kernel/kthread.c:464
       ret_from_fork+0x4e/0x80 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  &disk->open_mutex --> &nbd->config_lock --> &set->update_nr_hwq_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&set->update_nr_hwq_lock);
                               lock(&nbd->config_lock);
                               lock(&set->update_nr_hwq_lock);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

3 locks held by kworker/u4:1/13:
 #0: ffff888000b13148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3213 [inline]
 #0: ffff888000b13148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_scheduled_works+0x9b1/0x17a0 kernel/workqueue.c:3319
 #1: ffffc900001f7c60 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3214 [inline]
 #1: ffffc900001f7c60 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ec/0x17a0 kernel/workqueue.c:3319
 #2: ffff888053877188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

stack backtrace:
CPU: 0 UID: 0 PID: 13 Comm: kworker/u4:1 Not tainted 6.15.0-syzkaller-g914873bc7df9-dirty #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: nbd-del nbd_dev_remove_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:601 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
 __del_gendisk+0x129/0x9e0 block/genhd.c:706
 del_gendisk+0xe8/0x160 block/genhd.c:819
 nbd_dev_remove drivers/block/nbd.c:268 [inline]
 nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xade/0x17a0 kernel/workqueue.c:3319
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x4e/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
wlan0: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
wlan0: Creating new IBSS network, BSSID 50:50:50:50:50:50
wlan1: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
wlan1: Creating new IBSS network, BSSID 50:50:50:50:50:50


Tested on:

commit:         914873bc Merge tag 'x86-build-2025-05-25' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=141fbdf4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=eeb82b5d1d67d535
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13f7bdf4580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

drivers/block/nbd.c:1707:4: error: use of undeclared identifier 'retuen'
drivers/block/nbd.c:1712:4: error: use of undeclared identifier 'retuen'; did you mean 'return'?
drivers/block/nbd.c:1719:3: error: use of undeclared identifier 'retuen'


Tested on:

commit:         feacb177 Merge tag 'sched_ext-for-6.16' of git://git.k..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=fd18a1001092f95b
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
patch:          https://syzkaller.appspot.com/x/patch.diff?x=11e70bf4580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in __del_gendisk

======================================================
WARNING: possible circular locking dependency detected
6.15.0-syzkaller-g90b83efa6701-dirty #0 Not tainted
------------------------------------------------------
kworker/u4:2/31 is trying to acquire lock:
ffff888000617358 (&disk->open_mutex){+.+.}-{4:4}, at: __del_gendisk+0x129/0x9e0 block/genhd.c:706

but task is already holding lock:
ffff88803f055188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&set->update_nr_hwq_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
       blk_mq_update_nr_hw_queues+0x3b/0x14c0 block/blk-mq.c:5041
       nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
       nbd_genl_connect+0x1250/0x1930 drivers/block/nbd.c:2203
       genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2534
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
       netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
       sock_sendmsg_nosec net/socket.c:712 [inline]
       __sock_sendmsg+0x21c/0x270 net/socket.c:727
       ____sys_sendmsg+0x505/0x830 net/socket.c:2566
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
       __sys_sendmsg net/socket.c:2652 [inline]
       __do_sys_sendmsg net/socket.c:2657 [inline]
       __se_sys_sendmsg net/socket.c:2655 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&nbd->config_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       nbd_open+0x2c3/0x5f0 drivers/block/nbd.c:1704
       blkdev_get_whole+0x98/0x510 block/bdev.c:730
       bdev_open+0x31e/0xd30 block/bdev.c:957
       blkdev_open+0x3a8/0x510 block/fops.c:676
       do_dentry_open+0xdf0/0x1970 fs/open.c:964
       vfs_open+0x3b/0x340 fs/open.c:1094
       do_open fs/namei.c:3887 [inline]
       path_openat+0x2ee5/0x3830 fs/namei.c:4046
       do_filp_open+0x1fa/0x410 fs/namei.c:4073
       do_sys_openat2+0x121/0x1c0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&disk->open_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       __del_gendisk+0x129/0x9e0 block/genhd.c:706
       del_gendisk+0xe8/0x160 block/genhd.c:819
       nbd_dev_remove drivers/block/nbd.c:268 [inline]
       nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
       process_one_work kernel/workqueue.c:3238 [inline]
       process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
       kthread+0x70e/0x8a0 kernel/kthread.c:464
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  &disk->open_mutex --> &nbd->config_lock --> &set->update_nr_hwq_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&set->update_nr_hwq_lock);
                               lock(&nbd->config_lock);
                               lock(&set->update_nr_hwq_lock);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

3 locks held by kworker/u4:2/31:
 #0: ffff88801f97e148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3213 [inline]
 #0: ffff88801f97e148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3321
 #1: ffffc90000527bc0 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3214 [inline]
 #1: ffffc90000527bc0 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3321
 #2: ffff88803f055188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818

stack backtrace:
CPU: 0 UID: 0 PID: 31 Comm: kworker/u4:2 Not tainted 6.15.0-syzkaller-g90b83efa6701-dirty #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: nbd-del nbd_dev_remove_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:601 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
 __del_gendisk+0x129/0x9e0 block/genhd.c:706
 del_gendisk+0xe8/0x160 block/genhd.c:819
 nbd_dev_remove drivers/block/nbd.c:268 [inline]
 nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         90b83efa Merge tag 'bpf-next-6.16' of git://git.kernel..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16892482580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=262b2977ef00756b
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1345dbf4580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

syzbot has bisected this issue to:

commit f1be1788a32e8fa63416ad4518bbd1a85a825c9d
Author: Ming Lei <ming.lei@redhat.com>
Date:   Fri Oct 25 00:37:20 2024 +0000

    block: model freeze & enter queue as lock for supporting lockdep

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1024db0c580000
start commit:   e0fca6f2cebf net: mana: Record doorbell physical address i..
git tree:       net
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1224db0c580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1424db0c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d11f52d3049c3790
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=132f8dd4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14aac182580000

Reported-by: syzbot+2e9e529ac0b319316453@syzkaller.appspotmail.com
Fixes: f1be1788a32e ("block: model freeze & enter queue as lock for supporting lockdep")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[Ming Lei]

On Mon, May 26, 2025 at 08:12:27PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    ddddf9d64f73 Merge tag 'perf-core-2025-05-25' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12f87882580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fd18a1001092f95b
> dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
> compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11825df4580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17fb7ad4580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-ddddf9d6.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/bc551d1d4e46/vmlinux-ddddf9d6.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d26a6de23b0e/bzImage-ddddf9d6.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2e9e529ac0b319316453@syzkaller.appspotmail.com
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.15.0-syzkaller-01599-gddddf9d64f73 #0 Not tainted
> ------------------------------------------------------
> kworker/u4:9/1091 is trying to acquire lock:
> ffff888011362358 (&disk->open_mutex){+.+.}-{4:4}, at: __del_gendisk+0x129/0x9e0 block/genhd.c:706
> 
> but task is already holding lock:
> ffff88801bb55188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xe0/0x160 block/genhd.c:818
> 
> which lock already depends on the new lock.
> 

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 7bdc7eb808ea..aa249719fa7f 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1473,7 +1473,12 @@ static int nbd_start_device(struct nbd_device *nbd)
 		return -EINVAL;
 	}
 
-	blk_mq_update_nr_hw_queues(&nbd->tag_set, config->num_connections);
+	mutex_unlock(&nbd->config_lock);
+	blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
+	mutex_lock(&nbd->config_lock);
+	if (config->num_connections != num_connections)
+		return -EINVAL;
+
 	nbd->pid = task_pid_nr(current);
 
 	nbd_parse_flags(nbd);

Thanks,
Ming

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file block/genhd.c
patch: **** unexpected end of file in patch



Tested on:

commit:         a6923c06 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=921f306d77438390
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       
patch:          https://syzkaller.appspot.com/x/patch.diff?x=109c0aa2580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file block/genhd.c
patch: **** unexpected end of file in patch



Tested on:

commit:         a6923c06 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=921f306d77438390
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17bed834580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in del_gendisk

wlan1: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
wlan1: Creating new IBSS network, BSSID 50:50:50:50:50:50
======================================================
WARNING: possible circular locking dependency detected
6.16.0-syzkaller-ga6923c06a3b2-dirty #0 Not tainted
------------------------------------------------------
kworker/u8:2/36 is trying to acquire lock:
ffff888025106188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0xf0/0x180 block/genhd.c:823

but task is already holding lock:
ffff8880251060d8 (&set->tag_list_lock){+.+.}-{4:4}, at: del_gendisk+0xe8/0x180 block/genhd.c:822

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&set->tag_list_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760
       blk_mq_sysfs_register+0x196/0x530 block/blk-mq-sysfs.c:232
       blk_register_queue+0xf2/0x400 block/blk-sysfs.c:884
       __add_disk+0x677/0xd50 block/genhd.c:528
       add_disk_fwnode+0xfc/0x480 block/genhd.c:597
       <kernel::block::mq::gen_disk::GenDiskBuilder>::build::<rnull::NullBlkDevice> rust/kernel/block/mq/gen_disk.rs:160 [inline]
       <rnull::NullBlkModule as kernel::InPlaceModule>::init::{closure#0} drivers/block/rnull.rs:49 [inline]
       <rnull::NullBlkModule as kernel::InPlaceModule>::init+0x8ee/0xc00 drivers/block/rnull.rs:46
       rnull::__module_init::__module_init::__init drivers/block/rnull.rs:27 [inline]
       __rnull_mod_init+0x1a/0x70 drivers/block/rnull.rs:27
       do_one_initcall+0x233/0x820 init/main.c:1269
       do_initcall_level+0x104/0x190 init/main.c:1331
       do_initcalls+0x59/0xa0 init/main.c:1347
       kernel_init_freeable+0x334/0x4a0 init/main.c:1579
       kernel_init+0x1d/0x1d0 init/main.c:1469
       ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&set->update_nr_hwq_lock){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1522
       del_gendisk+0xf0/0x180 block/genhd.c:823
       nbd_dev_remove drivers/block/nbd.c:268 [inline]
       nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
       process_one_work kernel/workqueue.c:3236 [inline]
       process_scheduled_works+0xade/0x17b0 kernel/workqueue.c:3319
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
       kthread+0x711/0x8a0 kernel/kthread.c:464
       ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&set->tag_list_lock);
                               lock(&set->update_nr_hwq_lock);
                               lock(&set->tag_list_lock);
  rlock(&set->update_nr_hwq_lock);

 *** DEADLOCK ***

3 locks held by kworker/u8:2/36:
 #0: ffff888025c60148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3211 [inline]
 #0: ffff888025c60148 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3319
 #1: ffffc90000ac7bc0 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
 #1: ffffc90000ac7bc0 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3319
 #2: ffff8880251060d8 (&set->tag_list_lock){+.+.}-{4:4}, at: del_gendisk+0xe8/0x180 block/genhd.c:822

stack backtrace:
CPU: 0 UID: 0 PID: 36 Comm: kworker/u8:2 Not tainted 6.16.0-syzkaller-ga6923c06a3b2-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: nbd-del nbd_dev_remove_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 down_read+0x46/0x2e0 kernel/locking/rwsem.c:1522
 del_gendisk+0xf0/0x180 block/genhd.c:823
 nbd_dev_remove drivers/block/nbd.c:268 [inline]
 nbd_dev_remove_work+0x47/0xe0 drivers/block/nbd.c:284
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xade/0x17b0 kernel/workqueue.c:3319
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         a6923c06 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1346dcf0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=18eb6d916c138763
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=11010aa2580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

block/genhd.c:743:19: error: use of undeclared identifier 'set'
block/genhd.c:745:17: error: use of undeclared identifier 'set'


Tested on:

commit:         186f3edf Merge tag 'pinctrl-v6.17-1' of git://git.kern..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=921f306d77438390
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=120b0aa2580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

block/genhd.c:743:19: error: use of undeclared identifier 'set'
block/genhd.c:745:17: error: use of undeclared identifier 'set'


Tested on:

commit:         186f3edf Merge tag 'pinctrl-v6.17-1' of git://git.kern..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=921f306d77438390
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10b2a2a2580000

Re: [syzbot] [block?] possible deadlock in __del_gendisk

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: MAX_LOCKDEP_KEYS too low!

BUG: MAX_LOCKDEP_KEYS too low!
turning off the locking correctness validator.
CPU: 0 UID: 0 PID: 17006 Comm: syz.0.1967 Not tainted 6.16.0-syzkaller-g186f3edfdd41-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 register_lock_class+0x2e8/0x320 kernel/locking/lockdep.c:1332
 __lock_acquire+0x99/0xd20 kernel/locking/lockdep.c:5112
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 blk_freeze_acquire_lock block/blk.h:738 [inline]
 blk_freeze_queue_start block/blk-mq.c:184 [inline]
 blk_mq_freeze_queue_nomemsave+0xd5/0x120 block/blk-mq.c:205
 blk_mq_freeze_queue include/linux/blk-mq.h:934 [inline]
 elevator_change+0xd5/0x320 block/elevator.c:666
 elevator_set_default+0x186/0x260 block/elevator.c:742
 blk_register_queue+0x35d/0x400 block/blk-sysfs.c:905
 __add_disk+0x677/0xd50 block/genhd.c:528
 add_disk_fwnode+0xfc/0x480 block/genhd.c:597
 add_disk include/linux/blkdev.h:773 [inline]
 nbd_dev_add+0x717/0xae0 drivers/block/nbd.c:1973
 nbd_genl_connect+0x919/0x18f0 drivers/block/nbd.c:2114
 genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
 ____sys_sendmsg+0x505/0x830 net/socket.c:2614
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
 __sys_sendmsg net/socket.c:2700 [inline]
 __do_sys_sendmsg net/socket.c:2705 [inline]
 __se_sys_sendmsg net/socket.c:2703 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe578b8e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe579a4d038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fe578db5fa0 RCX: 00007fe578b8e929
RDX: 0000000020000000 RSI: 0000200000001ac0 RDI: 0000000000000004
RBP: 00007fe578c10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fe578db5fa0 R15: 00007ffe9f356178
 </TASK>


Tested on:

commit:         186f3edf Merge tag 'pinctrl-v6.17-1' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10ea7f82580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=18eb6d916c138763
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10eddcf0580000