random: sshd: uninitialized urandom read (32 bytes read, 125 bits of entropy available)
random: sshd: uninitialized urandom read (32 bytes read, 127 bits of entropy available)
IPVS: Creating netns size=2552 id=1

======================================================
[ INFO: possible circular locking dependency detected ]
4.4.125-g38f41ec #21 Not tainted
-------------------------------------------------------
syz-executor0/3639 is trying to acquire lock:
 (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81cadaae>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189

but task is already holding lock:
 (&lo->lo_ctl_mutex#2){+.+.+.}, at: [<ffffffff82423b29>] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1526

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff8123dcae>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff8377039b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8377039b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
       [<ffffffff82424af5>] __lo_release drivers/block/loop.c:1579 [inline]
       [<ffffffff82424af5>] lo_release+0x85/0x160 drivers/block/loop.c:1602
       [<ffffffff815d4047>] __blkdev_put+0x5f7/0x7e0 fs/block_dev.c:1535
       [<ffffffff815d50a5>] blkdev_put+0x85/0x550 fs/block_dev.c:1600
       [<ffffffff815d55fb>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1607
       [<ffffffff81523f43>] __fput+0x233/0x6d0 fs/file_table.c:208
       [<ffffffff81524465>] ____fput+0x15/0x20 fs/file_table.c:244
       [<ffffffff8118bd44>] task_work_run+0x104/0x180 kernel/task_work.c:115
       [<ffffffff8100361d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
       [<ffffffff8100361d>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:252
       [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline]
       [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:348
       [<ffffffff83779af5>] int_ret_from_sys_call+0x25/0xa3

       [<ffffffff8123dcae>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff8377039b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8377039b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
       [<ffffffff8241d09b>] lo_open+0x1b/0xa0 drivers/block/loop.c:1559
       [<ffffffff815d44dc>] __blkdev_get+0x2ac/0xdf0 fs/block_dev.c:1213
       [<ffffffff815d62ad>] blkdev_get+0x33d/0x940 fs/block_dev.c:1353
       [<ffffffff815d6ab5>] blkdev_open+0x1a5/0x250 fs/block_dev.c:1508
       [<ffffffff8151881b>] do_dentry_open+0x59b/0xba0 fs/open.c:749
       [<ffffffff8151c0e0>] vfs_open+0x110/0x210 fs/open.c:862
       [<ffffffff8154d373>] do_last fs/namei.c:3221 [inline]
       [<ffffffff8154d373>] path_openat+0x923/0x3940 fs/namei.c:3357
       [<ffffffff81553017>] do_filp_open+0x197/0x290 fs/namei.c:3392
       [<ffffffff8151cab9>] do_sys_open+0x369/0x660 fs/open.c:1038
       [<ffffffff8151cddd>] SYSC_open fs/open.c:1056 [inline]
       [<ffffffff8151cddd>] SyS_open+0x2d/0x40 fs/open.c:1051
       [<ffffffff83779965>] entry_SYSCALL_64_fastpath+0x22/0x9e

       [<ffffffff8123b00f>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff8123b00f>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff8123b00f>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff8123b00f>] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213
       [<ffffffff8123dcae>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff8377039b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8377039b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
       [<ffffffff81cadaae>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
       [<ffffffff8241e6c8>] loop_reread_partitions+0x78/0xe0 drivers/block/loop.c:645
       [<ffffffff8241f0c5>] loop_set_status+0x995/0xfc0 drivers/block/loop.c:1175
       [<ffffffff8241f78a>] loop_set_status_compat+0x9a/0x100 drivers/block/loop.c:1499
       [<ffffffff82423b34>] lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1527
       [<ffffffff81cfa844>] compat_blkdev_ioctl+0x3d4/0x3b10 block/compat_ioctl.c:751
       [<ffffffff8161efea>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
       [<ffffffff8161efea>] compat_SyS_ioctl+0x28a/0x2540 fs/compat_ioctl.c:1544
       [<ffffffff81006d91>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
       [<ffffffff81006d91>] do_fast_syscall_32+0x321/0x8a0 arch/x86/entry/common.c:459
       [<ffffffff8377b2aa>] sysenter_flags_fixed+0xd/0x17

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-executor0/3639:
 #0:  (&lo->lo_ctl_mutex#2){+.+.+.}, at: [<ffffffff82423b29>] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1526

stack backtrace:
CPU: 1 PID: 3639 Comm: syz-executor0 Not tainted 4.4.125-g38f41ec #21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 f62b31014b8dc8c4 ffff8801ce2c75e8 ffffffff81d067bd
 ffffffff85188b10 ffffffff851880f0 ffffffff851b0fb0 ffff8800b27e0908
 ffff8800b27e0000 ffff8801ce2c7630 ffffffff81234081 ffff8800b27e0908
Call Trace:
 [<ffffffff81d067bd>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d067bd>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81234081>] print_circular_bug+0x271/0x310 kernel/locking/lockdep.c:1226
 [<ffffffff8123b00f>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff8123b00f>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff8123b00f>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff8123b00f>] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213
 [<ffffffff8123dcae>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
 [<ffffffff8377039b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff8377039b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
 [<ffffffff81cadaae>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
 [<ffffffff8241e6c8>] loop_reread_partitions+0x78/0xe0 drivers/block/loop.c:645
 [<ffffffff8241f0c5>] loop_set_status+0x995/0xfc0 drivers/block/loop.c:1175
 [<ffffffff8241f78a>] loop_set_status_compat+0x9a/0x100 drivers/block/loop.c:1499
 [<ffffffff82423b34>] lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1527
 [<ffffffff81cfa844>] compat_blkdev_ioctl+0x3d4/0x3b10 block/compat_ioctl.c:751
 [<ffffffff8161efea>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff8161efea>] compat_SyS_ioctl+0x28a/0x2540 fs/compat_ioctl.c:1544
 [<ffffffff81006d91>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
 [<ffffffff81006d91>] do_fast_syscall_32+0x321/0x8a0 arch/x86/entry/common.c:459
 [<ffffffff8377b2aa>] sysenter_flags_fixed+0xd/0x17