======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.18/6018 is trying to acquire lock:
ffff88801b2d8220 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_iop_getattr+0x9e/0x450 fs/kernfs/inode.c:193

but task is already holding lock:
ffff8880225962c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:934 [inline]
ffff8880225962c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: loop_change_fd drivers/block/loop.c:594 [inline]
ffff8880225962c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: lo_ioctl+0x16cc/0x1c10 drivers/block/loop.c:1543

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}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       blk_alloc_queue+0x538/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4400 [inline]
       __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4447
       loop_add+0x411/0xad0 drivers/block/loop.c:2043
       loop_init+0xd9/0x170 drivers/block/loop.c:2278
       do_one_initcall+0x236/0x820 init/main.c:1271
       do_initcall_level+0x104/0x190 init/main.c:1333
       do_initcalls+0x59/0xa0 init/main.c:1349
       kernel_init_freeable+0x334/0x4b0 init/main.c:1581
       kernel_init+0x1d/0x1d0 init/main.c:1471
       ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __fs_reclaim_acquire mm/page_alloc.c:4234 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4248
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4142 [inline]
       slab_alloc_node mm/slub.c:4220 [inline]
       kmem_cache_alloc_noprof+0x44/0x3c0 mm/slub.c:4247
       __kernfs_iattrs+0xd9/0x320 fs/kernfs/inode.c:36
       kernfs_iattrs fs/kernfs/inode.c:61 [inline]
       __kernfs_setattr fs/kernfs/inode.c:74 [inline]
       kernfs_iop_setattr+0xea/0x3f0 fs/kernfs/inode.c:128
       notify_change+0xb36/0xe40 fs/attr.c:552
       do_truncate+0x1a4/0x220 fs/open.c:68
       handle_truncate fs/namei.c:3596 [inline]
       do_open fs/namei.c:3979 [inline]
       path_openat+0x306c/0x3830 fs/namei.c:4134
       do_filp_open+0x1fa/0x410 fs/namei.c:4161
       do_sys_openat2+0x121/0x1c0 fs/open.c:1435
       do_sys_open fs/open.c:1450 [inline]
       __do_sys_openat fs/open.c:1466 [inline]
       __se_sys_openat fs/open.c:1461 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1461
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}
:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
       kernfs_iop_getattr+0x9e/0x450 fs/kernfs/inode.c:193
       vfs_getattr_nosec+0x2e1/0x430 fs/stat.c:213
       loop_query_min_dio_size drivers/block/loop.c:465 [inline]
       loop_assign_backing_file+0x222/0x400 drivers/block/loop.c:518
       loop_change_fd drivers/block/loop.c:596 [inline]
       lo_ioctl+0x1738/0x1c10 drivers/block/loop.c:1543
       blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:705
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:
  &root->kernfs_iattr_rwsem --> 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);
  rlock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

3 locks held by syz.1.18/6018:
 #0: ffff88802267b400 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_global_lock_killable drivers/block/loop.c:118 [inline]
 #0: ffff88802267b400 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_change_fd drivers/block/loop.c:561 [inline]
 #0: ffff88802267b400 (&lo->lo_mutex){+.+.}-{4:4}, at: lo_ioctl+0x11c1/0x1c10 drivers/block/loop.c:1543
 #1: ffff8880225962c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:934 [inline]
 #1: ffff8880225962c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: loop_change_fd drivers/block/loop.c:594 [inline]
 #1: ffff8880225962c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: lo_ioctl+0x16cc/0x1c10 drivers/block/loop.c:1543
 #2: ffff888022596300 (&q->q_usage_counter(queue)#8){+.+.}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:934 [inline]
 #2: ffff888022596300 (&q->q_usage_counter(queue)#8){+.+.}-{0:0}, at: loop_change_fd drivers/block/loop.c:594 [inline]
 #2: ffff888022596300 (&q->q_usage_counter(queue)#8){+.+.}-{0:0}, at: lo_ioctl+0x16cc/0x1c10 drivers/block/loop.c:1543

stack backtrace:
CPU: 1 UID: 0 PID: 6018 Comm: syz.1.18 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+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
 kernfs_iop_getattr+0x9e/0x450 fs/kernfs/inode.c:193
 vfs_getattr_nosec+0x2e1/0x430 fs/stat.c:213
 loop_query_min_dio_size drivers/block/loop.c:465 [inline]
 loop_assign_backing_file+0x222/0x400 drivers/block/loop.c:518
 loop_change_fd drivers/block/loop.c:596 [inline]
 lo_ioctl+0x1738/0x1c10 drivers/block/loop.c:1543
 blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:705
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5595f8ec29
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:00007f5596d46038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f55961d5fa0 RCX: 00007f5595f8ec29
RDX: 0000000000000006 RSI: 0000000000004c06 RDI: 0000000000000003
RBP: 00007f5596011e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f55961d6038 R14: 00007f55961d5fa0 R15: 00007fff8c2f3b48
 </TASK>
