======================================================
[ INFO: possible circular locking dependency detected ]
4.4.161+ #1 Not tainted
-------------------------------------------------------
syz-executor112/2090 is trying to acquire lock:
 (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81a655de>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189

but task is already holding lock:
 (&lo->lo_ctl_mutex#2){+.+...}, at: [<ffffffff81d34190>] lo_compat_ioctl+0x110/0x140 drivers/block/loop.c:1542

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa5db>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa5db>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff81d34245>] __lo_release drivers/block/loop.c:1595 [inline]
       [<ffffffff81d34245>] lo_release+0x85/0x1a0 drivers/block/loop.c:1618
       [<ffffffff81547966>] __blkdev_put+0x636/0x840 fs/block_dev.c:1535
       [<ffffffff815489e5>] blkdev_put+0x85/0x560 fs/block_dev.c:1600
       [<ffffffff81548f4b>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1607
       [<ffffffff81496de5>] __fput+0x235/0x6f0 fs/file_table.c:208
       [<ffffffff81497325>] ____fput+0x15/0x20 fs/file_table.c:244
       [<ffffffff8112f19f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
       [<ffffffff81003edd>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
       [<ffffffff81003edd>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:254
       [<ffffffff81005924>] prepare_exit_to_usermode arch/x86/entry/common.c:287 [inline]
       [<ffffffff81005924>] syscall_return_slowpath+0x254/0x2d0 arch/x86/entry/common.c:352
       [<ffffffff82705cad>] int_ret_from_sys_call+0x25/0xa3

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa5db>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa5db>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff81d2a0eb>] lo_open+0x1b/0xa0 drivers/block/loop.c:1575
       [<ffffffff81547e1e>] __blkdev_get+0x2ae/0xdf0 fs/block_dev.c:1213
       [<ffffffff8154abea>] blkdev_get+0x2da/0x920 fs/block_dev.c:1353
       [<ffffffff8154b445>] blkdev_open+0x1a5/0x250 fs/block_dev.c:1508
       [<ffffffff8148bc2d>] do_dentry_open+0x38d/0xbd0 fs/open.c:749
       [<ffffffff8148f39a>] vfs_open+0x12a/0x210 fs/open.c:862
       [<ffffffff814bef7c>] do_last fs/namei.c:3222 [inline]
       [<ffffffff814bef7c>] path_openat+0x50c/0x39a0 fs/namei.c:3359
       [<ffffffff814c60a7>] do_filp_open+0x197/0x270 fs/namei.c:3393
       [<ffffffff8148fcbc>] do_sys_open+0x31c/0x610 fs/open.c:1038
       [<ffffffff8148ffdd>] SYSC_open fs/open.c:1056 [inline]
       [<ffffffff8148ffdd>] SyS_open+0x2d/0x40 fs/open.c:1051
       [<ffffffff82705b21>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff811ff31c>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff811ff31c>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff811ff31c>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff811ff31c>] __lock_acquire+0x3e6c/0x5f10 kernel/locking/lockdep.c:3213
       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa5db>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa5db>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff81a655de>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
       [<ffffffff81d2b71c>] loop_reread_partitions+0x7c/0x90 drivers/block/loop.c:648
       [<ffffffff81d2c1ae>] loop_set_status+0xa7e/0xfe0 drivers/block/loop.c:1191
       [<ffffffff81d2c7aa>] loop_set_status_compat+0x9a/0xf0 drivers/block/loop.c:1515
       [<ffffffff81d3419b>] lo_compat_ioctl+0x11b/0x140 drivers/block/loop.c:1543
       [<ffffffff81a92e24>] compat_blkdev_ioctl+0x3a4/0x3546 block/compat_ioctl.c:751
       [<ffffffff8159376f>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
       [<ffffffff8159376f>] compat_SyS_ioctl+0x4af/0x2220 fs/compat_ioctl.c:1544
       [<ffffffff8100629e>] do_syscall_32_irqs_on arch/x86/entry/common.c:396 [inline]
       [<ffffffff8100629e>] do_fast_syscall_32+0x31e/0xa80 arch/x86/entry/common.c:463
       [<ffffffff82707290>] sysenter_flags_fixed+0xd/0x1a

other info that might help us debug this:

Chain exists of:
 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&lo->lo_ctl_mutex#2);
                               lock(loop_index_mutex);
                               lock(&lo->lo_ctl_mutex#2);
  lock(&bdev->bd_mutex);

 *** DEADLOCK ***

1 lock held by syz-executor112/2090:
 #0:  (&lo->lo_ctl_mutex#2){+.+...}, at: [<ffffffff81d34190>] lo_compat_ioctl+0x110/0x140 drivers/block/loop.c:1542

stack backtrace:
CPU: 0 PID: 2090 Comm: syz-executor112 Not tainted 4.4.161+ #1
 0000000000000000 0d8a8ea2c3f694a0 ffff8801d42f7608 ffffffff81a9969d
 ffffffff83a99850 ffffffff83abf110 ffffffff83a98ad0 ffff8800b6b220a8
 ffff8800b6b217c0 ffff8801d42f7650 ffffffff813a856a 0000000000000001
Call Trace:
 [<ffffffff81a9969d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81a9969d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff813a856a>] print_circular_bug.cold.34+0x2f7/0x432 kernel/locking/lockdep.c:1226
 [<ffffffff811ff31c>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff811ff31c>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff811ff31c>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff811ff31c>] __lock_acquire+0x3e6c/0x5f10 kernel/locking/lockdep.c:3213
 [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff826fa5db>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff826fa5db>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
 [<ffffffff81a655de>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
 [<ffffffff81d2b71c>] loop_reread_partitions+0x7c/0x90 drivers/block/loop.c:648
 [<ffffffff81d2c1ae>] loop_set_status+0xa7e/0xfe0 drivers/block/loop.c:1191
 [<ffffffff81d2c7aa>] loop_set_status_compat+0x9a/0xf0 drivers/block/loop.c:1515
 [<ffffffff81d3419b>] lo_compat_ioctl+0x11b/0x140 drivers/block/loop.c:1543
 [<ffffffff81a92e24>] compat_blkdev_ioctl+0x3a4/0x3546 block/compat_ioctl.c:751
 [<ffffffff8159376f>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff8159376f>] compat_SyS_ioctl+0x4af/0x2220 fs/compat_ioctl.c:1544
 [<ffffffff8100629e>] do_syscall_32_irqs_on arch/x86/entry/common.c:396 [inline]
 [<ffffffff8100629e>] do_fast_syscall_32+0x31e/0xa80 arch/x86/entry/common.c:463
 [<ffffffff82707290>] sysenter_flags_fixed+0xd/0x1a