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

syzbot
2025-04-03T08:34:25Z

syzbot has found a reproducer for the following issue on:

HEAD commit: a1b5bd45d4ee Merge tag 'usb-6.15-rc1' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1711cfb0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=adffebefc9feb9d6
dashboard link: https://syzkaller.appspot.com/bug?extid=9dd7dbb1a4b915dee638
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12ee494c580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13df5998580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-a1b5bd45.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/588b4d489b63/vmlinux-a1b5bd45.xz
kernel image: https://storage.googleapis.com/syzbot-assets/51ead797f7ae/bzImage-a1b5bd45.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9dd7dbb1a4b915dee638@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.14.0-syzkaller-12886-ga1b5bd45d4ee #0 Not tainted
------------------------------------------------------
syz-executor170/5939 is trying to acquire lock:
ffffffff906953a8 (uevent_sock_mutex){+.+.}-{4:4}, at: uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
ffffffff906953a8 (uevent_sock_mutex){+.+.}-{4:4}, at: kobject_uevent_net_broadcast lib/kobject_uevent.c:410 [inline]
ffffffff906953a8 (uevent_sock_mutex){+.+.}-{4:4}, at: kobject_uevent_env+0xb36/0x1870 lib/kobject_uevent.c:608

but task is already holding lock:
ffff888025aa6228 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:215

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}:
blk_alloc_queue+0x619/0x760 block/blk-core.c:461
blk_mq_alloc_queue+0x179/0x290 block/blk-mq.c:4349
__blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4396
loop_add+0x496/0xb70 drivers/block/loop.c:2067
loop_init+0x164/0x270 drivers/block/loop.c:2302
do_one_initcall+0x120/0x6e0 init/main.c:1257
do_initcall_level init/main.c:1319 [inline]
do_initcalls init/main.c:1335 [inline]
do_basic_setup init/main.c:1354 [inline]
kernel_init_freeable+0x5c2/0x900 init/main.c:1567
kernel_init+0x1c/0x2b0 init/main.c:1457
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire mm/page_alloc.c:4028 [inline]
fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:4042
might_alloc include/linux/sched/mm.h:318 [inline]
slab_pre_alloc_hook mm/slub.c:4102 [inline]
slab_alloc_node mm/slub.c:4180 [inline]
kmem_cache_alloc_node_noprof+0x57/0x3b0 mm/slub.c:4252
__alloc_skb+0x2b2/0x380 net/core/skbuff.c:658
alloc_skb include/linux/skbuff.h:1340 [inline]
alloc_uevent_skb+0x7d/0x210 lib/kobject_uevent.c:289
uevent_net_broadcast_untagged lib/kobject_uevent.c:326 [inline]
kobject_uevent_net_broadcast lib/kobject_uevent.c:410 [inline]
kobject_uevent_env+0xca4/0x1870 lib/kobject_uevent.c:608
kobject_synth_uevent+0x7d4/0x8a0 lib/kobject_uevent.c:207
bus_uevent_store+0x3d/0x90 drivers/base/bus.c:832
bus_attr_store+0x71/0xb0 drivers/base/bus.c:172
sysfs_kf_write+0xef/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x351/0x510 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:591 [inline]
vfs_write+0x5ba/0x1180 fs/read_write.c:684
ksys_write+0x12a/0x240 fs/read_write.c:736
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x260 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 kernel/locking/lockdep.c:3909 [inline]
__lock_acquire+0x1173/0x1ba0 kernel/locking/lockdep.c:5235
lock_acquire kernel/locking/lockdep.c:5866 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
__mutex_lock_common kernel/locking/mutex.c:601 [inline]
__mutex_lock+0x199/0xb90 kernel/locking/mutex.c:746
uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
kobject_uevent_net_broadcast lib/kobject_uevent.c:410 [inline]
kobject_uevent_env+0xb36/0x1870 lib/kobject_uevent.c:608
loop_set_size drivers/block/loop.c:211 [inline]
loop_set_size drivers/block/loop.c:208 [inline]
loop_set_status+0x9c7/0xb90 drivers/block/loop.c:1306
loop_set_status_old+0x162/0x1d0 drivers/block/loop.c:1405
lo_ioctl+0x695/0x26d0 drivers/block/loop.c:1575
blkdev_ioctl+0x274/0x6d0 block/ioctl.c:698
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x260 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-executor170/5939:
#0: ffff888025c4fb68 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_set_status+0x2a/0xb90 drivers/block/loop.c:1275
#1: ffff888025aa6228 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:215
#2: ffff888025aa6260 (&q->q_usage_counter(queue)#20){+.+.}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:215

stack backtrace:
CPU: 0 UID: 0 PID: 5939 Comm: syz-executor170 Not tainted 6.14.0-syzkaller-12886-ga1b5bd45d4ee #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
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2079
check_noncircular+0x14c/0x170 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 kernel/locking/lockdep.c:3909 [inline]
__lock_acquire+0x1173/0x1ba0 kernel/locking/lockdep.c:5235
lock_acquire kernel/locking/lockdep.c:5866 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
__mutex_lock_common kernel/locking/mutex.c:601 [inline]
__mutex_lock+0x199/0xb90 kernel/locking/mutex.c:746
uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
kobject_uevent_net_broadcast lib/kobject_uevent.c:410 [inline]
kobject_uevent_env+0xb36/0x1870 lib/kobject_uevent.c:608
loop_set_size drivers/block/loop.c:211 [inline]
loop_set_size drivers/block/loop.c:208 [inline]
loop_set_status+0x9c7/0xb90 drivers/block/loop.c:1306
loop_set_status_old+0x162/0x1d0 drivers/block/loop.c:1405
lo_ioctl+0x695/0x26d0 drivers/block/loop.c:1575
blkdev_ioctl+0x274/0x6d0 block/ioctl.c:698
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5b0284a229
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeda6302f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffeda6304c8 RCX: 00007f5b0284a229
RDX: 0000200000000080 RSI: 0000000000004c02 RDI: 0000000000000003
RBP: 00007f5b028bd610 R08: 00007ffeda6304c8 R09: 00007ffeda6304c8
R10: 00007ffeda6304c8 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffeda6304b8 R14: 0000000000000001 R15: 0000000000000001
</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.