syzbot

======================================================
WARNING: possible circular locking dependency detected
6.15.0-rc3-syzkaller-00283-gf1a3944c860b #0 Not tainted
------------------------------------------------------
syz-executor354/5827 is trying to acquire lock:
ffffffff8f657248 (uevent_sock_mutex){+.+.}-{4:4}, at: uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
ffffffff8f657248 (uevent_sock_mutex){+.+.}-{4:4}, at: kobject_uevent_net_broadcast+0x27e/0x560 lib/kobject_uevent.c:410

but task is already holding lock:
ffff888143fb27a8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:928 [inline]
ffff888143fb27a8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: loop_set_status+0x225/0xaf0 drivers/block/loop.c:1215

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#24){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
       blk_alloc_queue+0x538/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4348 [inline]
       __blk_mq_alloc_disk+0x164/0x350 block/blk-mq.c:4395
       loop_add+0x41d/0xae0 drivers/block/loop.c:1990
       loop_init+0x173/0x230 drivers/block/loop.c:2225
       do_one_initcall+0x233/0x820 init/main.c:1257
       do_initcall_level+0x137/0x1f0 init/main.c:1319
       do_initcalls+0x69/0xd0 init/main.c:1335
       kernel_init_freeable+0x3d9/0x570 init/main.c:1567
       kernel_init+0x1d/0x1d0 init/main.c:1457
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
       __fs_reclaim_acquire mm/page_alloc.c:4064 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4078
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4112 [inline]
       slab_alloc_node mm/slub.c:4190 [inline]
       kmem_cache_alloc_node_noprof+0x47/0x3c0 mm/slub.c:4262
       __alloc_skb+0x112/0x2d0 net/core/skbuff.c:658
       alloc_skb include/linux/skbuff.h:1340 [inline]
       alloc_uevent_skb+0x7d/0x230 lib/kobject_uevent.c:289
       uevent_net_broadcast_untagged lib/kobject_uevent.c:326 [inline]
       kobject_uevent_net_broadcast+0x2fa/0x560 lib/kobject_uevent.c:410
       kobject_uevent_env+0x55b/0x8c0 lib/kobject_uevent.c:608
       kobject_synth_uevent+0x527/0xb00 lib/kobject_uevent.c:207
       bus_uevent_store+0x115/0x170 drivers/base/bus.c:832
       kernfs_fop_write_iter+0x375/0x4f0 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:591 [inline]
       vfs_write+0x548/0xa90 fs/read_write.c:684
       ksys_write+0x145/0x250 fs/read_write.c:736
       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 (uevent_sock_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3166 [inline]
       check_prevs_add kernel/locking/lockdep.c:3285 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909
       __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
       kobject_uevent_net_broadcast+0x27e/0x560 lib/kobject_uevent.c:410
       kobject_uevent_env+0x55b/0x8c0 lib/kobject_uevent.c:608
       loop_set_size drivers/block/loop.c:211 [inline]
       loop_set_status+0x4d1/0xaf0 drivers/block/loop.c:1230
       lo_ioctl+0xb41/0x22e0 drivers/block/loop.c:-1
       blkdev_ioctl+0x5a5/0x6d0 block/ioctl.c:704
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:892
       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

other info that might help us debug this:

Chain exists of:
  uevent_sock_mutex --> fs_reclaim --> &q->q_usage_counter(io)#24

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#24);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#24);
  lock(uevent_sock_mutex);

 *** DEADLOCK ***

3 locks held by syz-executor354/5827:
 #0: ffff888024209368 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_set_status+0x2a/0xaf0 drivers/block/loop.c:1199
 #1: ffff888143fb27a8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:928 [inline]
 #1: ffff888143fb27a8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: loop_set_status+0x225/0xaf0 drivers/block/loop.c:1215
 #2: ffff888143fb27e0 (&q->q_usage_counter(queue)#20){+.+.}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:928 [inline]
 #2: ffff888143fb27e0 (&q->q_usage_counter(queue)#20){+.+.}-{0:0}, at: loop_set_status+0x225/0xaf0 drivers/block/loop.c:1215

stack backtrace:
CPU: 0 UID: 0 PID: 5827 Comm: syz-executor354 Not tainted 6.15.0-rc3-syzkaller-00283-gf1a3944c860b #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2079
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2211
 check_prev_add kernel/locking/lockdep.c:3166 [inline]
 check_prevs_add kernel/locking/lockdep.c:3285 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909
 __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
 __mutex_lock_common kernel/locking/mutex.c:601 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
 uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
 kobject_uevent_net_broadcast+0x27e/0x560 lib/kobject_uevent.c:410
 kobject_uevent_env+0x55b/0x8c0 lib/kobject_uevent.c:608
 loop_set_size drivers/block/loop.c:211 [inline]
 loop_set_status+0x4d1/0xaf0 drivers/block/loop.c:1230
 lo_ioctl+0xb41/0x22e0 drivers/block/loop.c:-1
 blkdev_ioctl+0x5a5/0x6d0 block/ioctl.c:704
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:892
 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
RIP: 0033:0x7f90cf63a939
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe0d3db488 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f90cf63a939
RDX: 00002000000001c0 RSI: 0000000000004c02 RDI: 0000000000000003
RBP: 00007f90cf6ad5f0 R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000000001
R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
 </TASK>