syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6001 is trying to acquire lock:
ffff888140450a20 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_iop_getattr+0x9e/0x450 fs/kernfs/inode.c:193

but task is already holding lock:
ffff888024ba4ca0 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:954 [inline]
ffff888024ba4ca0 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: loop_change_fd drivers/block/loop.c:595 [inline]
ffff888024ba4ca0 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: lo_ioctl+0x1a51/0x1fb0 drivers/block/loop.c:1546

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#26){++++}-{0:0}:
       blk_alloc_queue+0x52f/0x610 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4415 [inline]
       __blk_mq_alloc_disk+0x197/0x390 block/blk-mq.c:4462
       loop_add+0x482/0xb40 drivers/block/loop.c:2050
       loop_init+0xd9/0x170 drivers/block/loop.c:2289
       do_one_initcall+0x250/0x840 init/main.c:1378
       do_initcall_level+0x104/0x190 init/main.c:1440
       do_initcalls+0x59/0xa0 init/main.c:1456
       kernel_init_freeable+0x2a6/0x3d0 init/main.c:1688
       kernel_init+0x1d/0x1d0 init/main.c:1578
       ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #1 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4331 [inline]
       fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4345
       might_alloc include/linux/sched/mm.h:317 [inline]
       slab_pre_alloc_hook mm/slub.c:4904 [inline]
       slab_alloc_node mm/slub.c:5239 [inline]
       kmem_cache_alloc_noprof+0x45/0x6e0 mm/slub.c:5270
       __kernfs_iattrs+0xdf/0x340 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+0xc1a/0xf40 fs/attr.c:546
       do_truncate+0x1c2/0x250 fs/open.c:68
       handle_truncate fs/namei.c:4244 [inline]
       do_open fs/namei.c:4641 [inline]
       path_openat+0x360c/0x3e20 fs/namei.c:4796
       do_filp_open+0x22d/0x490 fs/namei.c:4823
       do_sys_openat2+0x12f/0x220 fs/open.c:1430
       do_sys_open fs/open.c:1436 [inline]
       __do_sys_openat fs/open.c:1452 [inline]
       __se_sys_openat fs/open.c:1447 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1447
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 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 kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x330 kernel/locking/lockdep.c:5868
       down_read+0x47/0x2e0 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:464 [inline]
       loop_assign_backing_file+0x27a/0x4b0 drivers/block/loop.c:517
       loop_change_fd drivers/block/loop.c:597 [inline]
       lo_ioctl+0x1acb/0x1fb0 drivers/block/loop.c:1546
       blkdev_ioctl+0x5e3/0x740 block/ioctl.c:792
       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+0xe2/0xf80 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)#26

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#26);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#26);
  rlock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

3 locks held by syz.0.17/6001:
 #0: ffff888024cb7448 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_global_lock_killable drivers/block/loop.c:118 [inline]
 #0: ffff888024cb7448 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_change_fd drivers/block/loop.c:562 [inline]
 #0: ffff888024cb7448 (&lo->lo_mutex){+.+.}-{4:4}, at: lo_ioctl+0x14c7/0x1fb0 drivers/block/loop.c:1546
 #1: ffff888024ba4ca0 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:954 [inline]
 #1: ffff888024ba4ca0 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: loop_change_fd drivers/block/loop.c:595 [inline]
 #1: ffff888024ba4ca0 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: lo_ioctl+0x1a51/0x1fb0 drivers/block/loop.c:1546
 #2: ffff888024ba4cd8 (&q->q_usage_counter(queue)#10){+.+.}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:954 [inline]
 #2: ffff888024ba4cd8 (&q->q_usage_counter(queue)#10){+.+.}-{0:0}, at: loop_change_fd drivers/block/loop.c:595 [inline]
 #2: ffff888024ba4cd8 (&q->q_usage_counter(queue)#10){+.+.}-{0:0}, at: lo_ioctl+0x1a51/0x1fb0 drivers/block/loop.c:1546

stack backtrace:
CPU: 1 UID: 0 PID: 6001 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x330 kernel/locking/lockdep.c:5868
 down_read+0x47/0x2e0 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:464 [inline]
 loop_assign_backing_file+0x27a/0x4b0 drivers/block/loop.c:517
 loop_change_fd drivers/block/loop.c:597 [inline]
 lo_ioctl+0x1acb/0x1fb0 drivers/block/loop.c:1546
 blkdev_ioctl+0x5e3/0x740 block/ioctl.c:792
 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+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fac2239aeb9
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:00007fff2df96ed8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fac22615fa0 RCX: 00007fac2239aeb9
RDX: 0000000000000005 RSI: 0000000000004c06 RDI: 0000000000000003
RBP: 00007fac22408c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fac22615fac R14: 00007fac22615fa0 R15: 00007fac22615fa0
 </TASK>