syzbot

======================================================
WARNING: possible circular locking dependency detected
6.16.0-syzkaller-12016-gbec077162bd0 #0 Not tainted
------------------------------------------------------
syz.3.299/8004 is trying to acquire lock:
ffff888025d5d468 (&q->elevator_lock){+.+.}-{4:4}, at: queue_requests_store+0x1c7/0x310 block/blk-sysfs.c:80

but task is already holding lock:
ffff888025d5cf28 (&q->q_usage_counter(io)#22){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:205

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&q->q_usage_counter(io)#22){++++}-{0:0}:
       blk_alloc_queue+0x619/0x760 block/blk-core.c:461
       blk_mq_alloc_queue+0x172/0x280 block/blk-mq.c:4400
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4447
       loop_add+0x490/0xb70 drivers/block/loop.c:2034
       loop_init+0x164/0x270 drivers/block/loop.c:2269
       do_one_initcall+0x120/0x6e0 init/main.c:1269
       do_initcall_level init/main.c:1331 [inline]
       do_initcalls init/main.c:1347 [inline]
       do_basic_setup init/main.c:1366 [inline]
       kernel_init_freeable+0x5c2/0x910 init/main.c:1579
       kernel_init+0x1c/0x2b0 init/main.c:1469
       ret_from_fork+0x5d7/0x6f0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4234 [inline]
       fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:4248
       might_alloc include/linux/sched/mm.h:318 [inline]
       prepare_alloc_pages+0x162/0x610 mm/page_alloc.c:4916
       __alloc_frozen_pages_noprof+0x18b/0x23f0 mm/page_alloc.c:5137
       __alloc_pages_noprof+0xb/0x1b0 mm/page_alloc.c:5182
       __alloc_pages_node_noprof include/linux/gfp.h:284 [inline]
       alloc_pages_node_noprof include/linux/gfp.h:311 [inline]
       pcpu_alloc_pages mm/percpu-vm.c:95 [inline]
       pcpu_populate_chunk+0x110/0xb00 mm/percpu-vm.c:285
       pcpu_alloc_noprof+0x86a/0x1470 mm/percpu.c:1870
       bpf_map_alloc_percpu+0x9a/0x4b0 kernel/bpf/syscall.c:558
       prealloc_init kernel/bpf/hashtab.c:336 [inline]
       htab_map_alloc+0x10ca/0x1570 kernel/bpf/hashtab.c:561
       map_create+0x58f/0x1f80 kernel/bpf/syscall.c:1480
       __sys_bpf+0x44d2/0x4de0 kernel/bpf/syscall.c:6011
       __do_sys_bpf kernel/bpf/syscall.c:6139 [inline]
       __se_sys_bpf kernel/bpf/syscall.c:6137 [inline]
       __x64_sys_bpf+0x78/0xc0 kernel/bpf/syscall.c:6137
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (pcpu_alloc_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
       pcpu_alloc_noprof+0xb4c/0x1470 mm/percpu.c:1782
       init_alloc_hint lib/sbitmap.c:16 [inline]
       sbitmap_init_node+0x2fd/0x770 lib/sbitmap.c:126
       sbitmap_queue_init_node+0x41/0x560 lib/sbitmap.c:438
       bt_alloc block/blk-mq-tag.c:542 [inline]
       blk_mq_init_tags+0x12d/0x2b0 block/blk-mq-tag.c:565
       blk_mq_alloc_rq_map block/blk-mq.c:3542 [inline]
       blk_mq_alloc_map_and_rqs+0x237/0xf60 block/blk-mq.c:4098
       blk_mq_sched_alloc_map_and_rqs block/blk-mq-sched.c:386 [inline]
       blk_mq_init_sched+0x30c/0x610 block/blk-mq-sched.c:485
       elevator_switch+0x1e1/0x7f0 block/elevator.c:595
       elevator_change+0x2ac/0x400 block/elevator.c:679
       elevator_set_default+0x2c4/0x360 block/elevator.c:742
       blk_register_queue+0x393/0x4f0 block/blk-sysfs.c:905
       __add_disk+0x74a/0xf00 block/genhd.c:528
       add_disk_fwnode+0x13f/0x5d0 block/genhd.c:597
       add_disk include/linux/blkdev.h:773 [inline]
       nbd_dev_add+0x783/0xbb0 drivers/block/nbd.c:1973
       nbd_init+0x181/0x320 drivers/block/nbd.c:2680
       do_one_initcall+0x120/0x6e0 init/main.c:1269
       do_initcall_level init/main.c:1331 [inline]
       do_initcalls init/main.c:1347 [inline]
       do_basic_setup init/main.c:1366 [inline]
       kernel_init_freeable+0x5c2/0x910 init/main.c:1579
       kernel_init+0x1c/0x2b0 init/main.c:1469
       ret_from_fork+0x5d7/0x6f0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&q->elevator_lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
       queue_requests_store+0x1c7/0x310 block/blk-sysfs.c:80
       queue_attr_store+0x26b/0x310 block/blk-sysfs.c:831
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x354/0x510 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x6c4/0x1150 fs/read_write.c:686
       ksys_write+0x12a/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x490 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:
  &q->elevator_lock --> 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(&q->elevator_lock);

 *** DEADLOCK ***

6 locks held by syz.3.299/8004:
 #0: ffff888032b5ad38 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2a2/0x370 fs/file.c:1232
 #1: ffff88807d542428 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:738
 #2: ffff888059aa1488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x510 fs/kernfs/file.c:325
 #3: ffff888025e27e18 (kn->active#111){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2b2/0x510 fs/kernfs/file.c:326
 #4: ffff888025d5cf28 (&q->q_usage_counter(io)#22){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:205
 #5: ffff888025d5cf60 (&q->q_usage_counter(queue)#21){+.+.}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:205

stack backtrace:
CPU: 1 UID: 0 PID: 8004 Comm: syz.3.299 Not tainted 6.16.0-syzkaller-12016-gbec077162bd0 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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:2043
 check_noncircular+0x14c/0x170 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 kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
 queue_requests_store+0x1c7/0x310 block/blk-sysfs.c:80
 queue_attr_store+0x26b/0x310 block/blk-sysfs.c:831
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x354/0x510 fs/kernfs/file.c:334
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x6c4/0x1150 fs/read_write.c:686
 ksys_write+0x12a/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdf3418ebe9
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:00007fdf35098038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fdf343b5fa0 RCX: 00007fdf3418ebe9
RDX: 0000000000000081 RSI: 0000200000000140 RDI: 0000000000000003
RBP: 00007fdf34211e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdf343b6038 R14: 00007fdf343b5fa0 R15: 00007ffd31a190f8
 </TASK>