syzbot

======================================================
WARNING: possible circular locking dependency detected
6.14.0-syzkaller-11125-g609706855d90 #0 Not tainted
------------------------------------------------------
syz.0.753/9197 is trying to acquire lock:
ffff8881437e2318 (&q->elevator_lock){+.+.}-{4:4}, at: queue_wb_lat_store+0x187/0x3d0 block/blk-sysfs.c:596

but task is already holding lock:
ffff8881437e1de8 (&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:3914 [inline]
       fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:3928
       might_alloc include/linux/sched/mm.h:318 [inline]
       xa_insert include/linux/xarray.h:783 [inline]
       blk_mq_init_hctx block/blk-mq.c:3924 [inline]
       blk_mq_alloc_and_init_hctx+0x503/0x11c0 block/blk-mq.c:4457
       blk_mq_realloc_hw_ctxs+0x8f6/0xc00 block/blk-mq.c:4486
       blk_mq_init_allocated_queue+0x3af/0x1230 block/blk-mq.c:4540
       blk_mq_alloc_queue+0x1c2/0x290 block/blk-mq.c:4353
       __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

-> #0 (&q->elevator_lock){+.+.}-{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
       queue_wb_lat_store+0x187/0x3d0 block/blk-sysfs.c:596
       queue_attr_store+0x270/0x310 block/blk-sysfs.c:799
       sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
       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

other info that might help us debug this:

Chain exists of:
  &q->elevator_lock --> 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(&q->elevator_lock);

 *** DEADLOCK ***

6 locks held by syz.0.753/9197:
 #0: ffff88806a44d278 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2a2/0x370 fs/file.c:1213
 #1: ffff888035a20420 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x12a/0x240 fs/read_write.c:736
 #2: ffff888061625888 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x510 fs/kernfs/file.c:325
 #3: ffff8880213fbb48 (kn->active#125){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2b2/0x510 fs/kernfs/file.c:326
 #4: ffff8881437e1de8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:215
 #5: ffff8881437e1e20 (&q->q_usage_counter(queue)#21){+.+.}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x15/0x20 block/blk-mq.c:215

stack backtrace:
CPU: 1 UID: 0 PID: 9197 Comm: syz.0.753 Not tainted 6.14.0-syzkaller-11125-g609706855d90 #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
 queue_wb_lat_store+0x187/0x3d0 block/blk-sysfs.c:596
 queue_attr_store+0x270/0x310 block/blk-sysfs.c:799
 sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
 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
RIP: 0033:0x7fb5d6d8d169
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:00007fb5d7bca038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fb5d6fa5fa0 RCX: 00007fb5d6d8d169
RDX: 0000000000000081 RSI: 0000200000000040 RDI: 0000000000000003
RBP: 00007fb5d6e0e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fb5d6fa5fa0 R15: 00007ffce0809d88
 </TASK>