[syzbot] [block?] possible deadlock in blk_mq_freeze_queue_nomemsave

syzbot
2025-03-31T13:34:24Z

Hello,

syzbot found the following issue on:

HEAD commit: aa918db707fb Merge tag 'bpf_try_alloc_pages' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1776ec3f980000
kernel config: https://syzkaller.appspot.com/x/.config?x=9c654e2bc7f36976
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

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/81273eda411b/disk-aa918db7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a2d1a79f3011/vmlinux-aa918db7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/df851fa81fd2/bzImage-aa918db7.xz

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

loop5: detected capacity change from 2048 to 64
======================================================
WARNING: possible circular locking dependency detected
6.14.0-syzkaller-10764-gaa918db707fb #0 Not tainted
------------------------------------------------------
syz.5.738/7855 is trying to acquire lock:
ffffffff9068dfe8 (uevent_sock_mutex){+.+.}-{4:4}, at: uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
ffffffff9068dfe8 (uevent_sock_mutex){+.+.}-{4:4}, at: kobject_uevent_net_broadcast lib/kobject_uevent.c:410 [inline]
ffffffff9068dfe8 (uevent_sock_mutex){+.+.}-{4:4}, at: kobject_uevent_env+0xb36/0x1870 lib/kobject_uevent.c:608

but task is already holding lock:
ffff888025874ea8 (&q->q_usage_counter(io)#22){++++}-{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)#22){++++}-{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+0x123/0x6e0 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+0x48/0x80 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:3914 [inline]
fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:3928
might_alloc include/linux/sched/mm.h:318 [inline]
slab_pre_alloc_hook mm/slub.c:4089 [inline]
slab_alloc_node mm/slub.c:4167 [inline]
kmem_cache_alloc_node_noprof+0x57/0x3b0 mm/slub.c:4239
__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+0x74/0xb0 drivers/base/bus.c:172
sysfs_kf_write+0x11a/0x170 fs/sysfs/file.c:139
kernfs_fop_write_iter+0x354/0x510 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:591 [inline]
vfs_write+0x5bd/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:587 [inline]
__mutex_lock+0x199/0xb90 kernel/locking/mutex.c:732
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
set_capacity_and_notify+0x1ca/0x240 block/genhd.c:102
loop_set_size drivers/block/loop.c:210 [inline]
loop_set_status+0x94a/0xb90 drivers/block/loop.c:1306
loop_set_status64 drivers/block/loop.c:1415 [inline]
lo_ioctl+0x729/0x26d0 drivers/block/loop.c:1582
blkdev_ioctl+0x277/0x6d0 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+0x193/0x200 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)#22

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&q->q_usage_counter(io)#22);
lock(fs_reclaim);
lock(&q->q_usage_counter(io)#22);
lock(uevent_sock_mutex);

*** DEADLOCK ***

3 locks held by syz.5.738/7855:
#0: ffff8880259e4b68 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_set_status+0x2a/0xb90 drivers/block/loop.c:1275
#1: ffff888025874ea8 (&q->q_usage_counter(io)#22){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:215
#2: ffff888025874ee0 (&q->q_usage_counter(queue)#21){+.+.}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:215

stack backtrace:
CPU: 0 UID: 0 PID: 7855 Comm: syz.5.738 Not tainted 6.14.0-syzkaller-10764-gaa918db707fb #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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:587 [inline]
__mutex_lock+0x199/0xb90 kernel/locking/mutex.c:732
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
set_capacity_and_notify+0x1ca/0x240 block/genhd.c:102
loop_set_size drivers/block/loop.c:210 [inline]
loop_set_status+0x94a/0xb90 drivers/block/loop.c:1306
loop_set_status64 drivers/block/loop.c:1415 [inline]
lo_ioctl+0x729/0x26d0 drivers/block/loop.c:1582
blkdev_ioctl+0x277/0x6d0 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+0x193/0x200 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: 0033:0x7f74ac58d169
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:00007f74ad427038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f74ac7a5fa0 RCX: 00007f74ac58d169
RDX: 00002000000007c0 RSI: 0000000000004c04 RDI: 0000000000000006
RBP: 00007f74ac60e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f74ac7a5fa0 R15: 00007ffc990fb088
</TASK>

---
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