possible deadlock in blkdev_reread_part

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 1ec8f1f0 Linux 4.14.111
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17f365bb200000
kernel config: https://syzkaller.appspot.com/x/.config?x=fdadf290ea9fc6f9
dashboard link: https://syzkaller.appspot.com/bug?extid=8717dc3c67074f156de2
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8717dc...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
4.14.111 #1 Not tainted
------------------------------------------------------
syz-executor.5/32668 is trying to acquire lock:
(&bdev->bd_mutex){+.+.}, at: [<ffffffff82ca511f>]
blkdev_reread_part+0x1f/0x40 block/ioctl.c:192

but task is already holding lock:
(&nbd->config_lock){+.+.}, at: [<ffffffff83742af4>] nbd_ioctl+0x134/0xae0
drivers/block/nbd.c:1289

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nbd->config_lock){+.+.}:
lock_acquire+0x16f/0x430 kernel/locking/lockdep.c:3994
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xe8/0x1470 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
nbd_open+0xf2/0x1f0 drivers/block/nbd.c:1337
__blkdev_get+0x2c9/0x1120 fs/block_dev.c:1472
blkdev_get+0xa8/0x8e0 fs/block_dev.c:1612
blkdev_open+0x1d1/0x260 fs/block_dev.c:1770
do_dentry_open+0x73e/0xeb0 fs/open.c:758
vfs_open+0x105/0x230 fs/open.c:872
do_last fs/namei.c:3425 [inline]
path_openat+0x8bd/0x3f70 fs/namei.c:3566
do_filp_open+0x18e/0x250 fs/namei.c:3600
do_sys_open+0x2c5/0x430 fs/open.c:1065
SYSC_open fs/open.c:1083 [inline]
SyS_open+0x2d/0x40 fs/open.c:1078
do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #1 (nbd_index_mutex){+.+.}:
lock_acquire+0x16f/0x430 kernel/locking/lockdep.c:3994
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xe8/0x1470 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
nbd_open+0x27/0x1f0 drivers/block/nbd.c:1324
__blkdev_get+0x2c9/0x1120 fs/block_dev.c:1472
blkdev_get+0xa8/0x8e0 fs/block_dev.c:1612
blkdev_open+0x1d1/0x260 fs/block_dev.c:1770
do_dentry_open+0x73e/0xeb0 fs/open.c:758
vfs_open+0x105/0x230 fs/open.c:872
do_last fs/namei.c:3425 [inline]
path_openat+0x8bd/0x3f70 fs/namei.c:3566
do_filp_open+0x18e/0x250 fs/namei.c:3600
do_sys_open+0x2c5/0x430 fs/open.c:1065
SYSC_open fs/open.c:1083 [inline]
SyS_open+0x2d/0x40 fs/open.c:1078
do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #0 (&bdev->bd_mutex){+.+.}:
check_prev_add kernel/locking/lockdep.c:1901 [inline]
check_prevs_add kernel/locking/lockdep.c:2018 [inline]
validate_chain kernel/locking/lockdep.c:2460 [inline]
__lock_acquire+0x2c89/0x45e0 kernel/locking/lockdep.c:3487
lock_acquire+0x16f/0x430 kernel/locking/lockdep.c:3994
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xe8/0x1470 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
blkdev_reread_part+0x1f/0x40 block/ioctl.c:192
nbd_bdev_reset drivers/block/nbd.c:1031 [inline]
nbd_clear_sock_ioctl drivers/block/nbd.c:1211 [inline]
__nbd_ioctl drivers/block/nbd.c:1227 [inline]
nbd_ioctl+0x807/0xae0 drivers/block/nbd.c:1296
__blkdev_driver_ioctl block/ioctl.c:297 [inline]
blkdev_ioctl+0x983/0x1880 block/ioctl.c:594
block_ioctl+0xde/0x120 fs/block_dev.c:1881
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x7b9/0x1070 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7

other info that might help us debug this:

Chain exists of:
&bdev->bd_mutex --> nbd_index_mutex --> &nbd->config_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&nbd->config_lock);
lock(nbd_index_mutex);
lock(&nbd->config_lock);
lock(&bdev->bd_mutex);

*** DEADLOCK ***

1 lock held by syz-executor.5/32668:
#0: (&nbd->config_lock){+.+.}, at: [<ffffffff83742af4>]
nbd_ioctl+0x134/0xae0 drivers/block/nbd.c:1289

stack backtrace:
CPU: 0 PID: 32668 Comm: syz-executor.5 Not tainted 4.14.111 #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x138/0x19c lib/dump_stack.c:53
print_circular_bug.isra.0.cold+0x1cc/0x28f kernel/locking/lockdep.c:1258
check_prev_add kernel/locking/lockdep.c:1901 [inline]
check_prevs_add kernel/locking/lockdep.c:2018 [inline]
validate_chain kernel/locking/lockdep.c:2460 [inline]
__lock_acquire+0x2c89/0x45e0 kernel/locking/lockdep.c:3487
lock_acquire+0x16f/0x430 kernel/locking/lockdep.c:3994
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xe8/0x1470 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
blkdev_reread_part+0x1f/0x40 block/ioctl.c:192
nbd_bdev_reset drivers/block/nbd.c:1031 [inline]
nbd_clear_sock_ioctl drivers/block/nbd.c:1211 [inline]
__nbd_ioctl drivers/block/nbd.c:1227 [inline]
nbd_ioctl+0x807/0xae0 drivers/block/nbd.c:1296
__blkdev_driver_ioctl block/ioctl.c:297 [inline]
blkdev_ioctl+0x983/0x1880 block/ioctl.c:594
block_ioctl+0xde/0x120 fs/block_dev.c:1881
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x7b9/0x1070 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4582f9
RSP: 002b:00007f6e7c6b2c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00000000004582f9
RDX: 0000000000000000 RSI: 000000000000ab04 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6e7c6b36d4
R13: 00000000004c1645 R14: 00000000004d3978 R15: 00000000ffffffff
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
net_ratelimit: 3 callbacks suppressed
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
Dead loop on virtual device ip6_vti0, fix it urgently!
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop2' (ffff8880a4a31220): fill_kobj_path: path
= '/devices/virtual/block/loop2'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
overlayfs: failed to resolve './file1': -2
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
ntfs: (device loop0): ntfs_fill_super(): Unable to determine device size.
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop5' (ffff8880a4ae8260): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop5' (ffff8880a4ae8260): fill_kobj_path: path
= '/devices/virtual/block/loop5'
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop4' (ffff8880a4ae3320): kobject_uevent_env
kobject: 'loop4' (ffff8880a4ae3320): fill_kobj_path: path
= '/devices/virtual/block/loop4'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop3' (ffff8880a4a4b2a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop3' (ffff8880a4a4b2a0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): fill_kobj_path: path
= '/devices/virtual/block/loop0'
kobject: 'loop1' (ffff8880a49c8920): kobject_uevent_env
kobject: 'loop1' (ffff8880a49c8920): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop2' (ffff8880a4a31220): kobject_uevent_env
kobject: 'loop0' (ffff8880a11d83a0): kobject_uevent_env


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: 1ec8f1f0 Linux 4.14.111
git tree: linux-4.14.y

console output: https://syzkaller.appspot.com/x/log.txt?x=178732dd200000

kernel config: https://syzkaller.appspot.com/x/.config?x=fdadf290ea9fc6f9
dashboard link: https://syzkaller.appspot.com/bug?extid=8717dc3c67074f156de2
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15778ded200000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13767d97200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8717dc...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
audit: type=1400 audit(1555004398.221:36): avc: denied { map } for
pid=6930 comm="syz-executor756" path="/root/syz-executor756537227"
dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1

======================================================
WARNING: possible circular locking dependency detected
4.14.111 #1 Not tainted
------------------------------------------------------

syz-executor756/6930 is trying to acquire lock:

1 lock held by syz-executor756/6930:

#0: (&nbd->config_lock){+.+.}, at: [<ffffffff83742af4>]
nbd_ioctl+0x134/0xae0 drivers/block/nbd.c:1289

stack backtrace:

CPU: 1 PID: 6930 Comm: syz-executor756 Not tainted 4.14.111 #1

RIP: 0033:0x443df9
RSP: 002b:00007fff73275bd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000443df9

RDX: 0000000000000000 RSI: 000000000000ab04 RDI: 0000000000000003

RBP: 00000000006ce018 R08: 0000000000000