======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.8/5734 is trying to acquire lock:
ffffffff8fe90da0 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_noprof+0x5f/0x600

but task is already holding lock:
ffff88810b948d30 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa3/0xd80

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->blkcg_mutex){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       blkcg_activate_policy+0x1cb/0x8e0
       blk_throtl_init+0x2f7/0x420
       tg_set_conf+0x1db/0x4e0
       cgroup_file_write+0x331/0x8f0
       kernfs_fop_write_iter+0x3a4/0x540
       vfs_write+0x612/0xba0
       ksys_write+0x150/0x270
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#66){++++}-{0:0}:
       blk_alloc_queue+0x544/0x690
       __blk_mq_alloc_disk+0x194/0x390
       null_add_dev+0xe82/0x1d70
       null_init+0x1e3/0x390
       do_one_initcall+0x250/0x870
       do_initcall_level+0x10a/0x1a0
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x29d/0x3e0
       kernel_init+0x22/0x1d0
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #0 (fs_reclaim){+.+.}-{0:0}:
       __lock_acquire+0x164c/0x2de0
       lock_acquire+0x115/0x350
       fs_reclaim_acquire+0x71/0x100
       kmem_cache_alloc_noprof+0x5f/0x600
       __radix_tree_preload+0x2df/0x870
       blkg_conf_prep+0x621/0xd80
       tg_set_conf+0x20b/0x4e0
       cgroup_file_write+0x331/0x8f0
       kernfs_fop_write_iter+0x3a4/0x540
       vfs_write+0x612/0xba0
       ksys_write+0x150/0x270
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  fs_reclaim --> &q->q_usage_counter(io)#66 --> &q->blkcg_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->blkcg_mutex);
                               lock(&q->q_usage_counter(io)#66);
                               lock(&q->blkcg_mutex);
  lock(fs_reclaim);

 *** DEADLOCK ***

locks held by syz.1.8/5734: 6, last CPU#1:
 #0: ffff88816f03f4f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff88816f8e2460 (sb_writers#10){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0
 #2: ffff88816955cc80 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d8/0x540
 #3: ffff8881094ff878 (kn->active#57){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x22b/0x540
 #4: ffff88810b948bb0 (&q->rq_qos_mutex){+.+.}-{4:4}, at: blkg_conf_open_bdev+0x2a8/0x3c0
 #5: ffff88810b948d30 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa3/0xd80

stack backtrace:
CPU: 1 UID: 0 PID: 5734 Comm: syz.1.8 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 print_circular_bug+0x2e2/0x300
 check_noncircular+0x12f/0x150
 __lock_acquire+0x164c/0x2de0
 lock_acquire+0x115/0x350
 fs_reclaim_acquire+0x71/0x100
 kmem_cache_alloc_noprof+0x5f/0x600
 __radix_tree_preload+0x2df/0x870
 blkg_conf_prep+0x621/0xd80
 tg_set_conf+0x20b/0x4e0
 cgroup_file_write+0x331/0x8f0
 kernfs_fop_write_iter+0x3a4/0x540
 vfs_write+0x612/0xba0
 ksys_write+0x150/0x270
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fecaeb9f559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fecacdee028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fecaee25fa0 RCX: 00007fecaeb9f559
RDX: 0000000000000006 RSI: 0000200000000180 RDI: 0000000000000005
RBP: 00007fecaec36b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fecaee26038 R14: 00007fecaee25fa0 R15: 00007ffe35d01828
 </TASK>
