syzbot

netlink: 4 bytes leftover after parsing attributes in process `syz-executor191'.
netlink: 4 bytes leftover after parsing attributes in process `syz-executor191'.
netlink: 4 bytes leftover after parsing attributes in process `syz-executor191'.
netlink: 4 bytes leftover after parsing attributes in process `syz-executor191'.
======================================================
WARNING: possible circular locking dependency detected
5.14.0-rc7-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor191/8426 is trying to acquire lock:
ffff88801e634518 (&disk->open_mutex){+.+.}-{3:3}, at: del_gendisk+0x8b/0x770 block/genhd.c:587

but task is already holding lock:
ffffffff8c4899c8 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock lib/refcount.c:118 [inline]
ffffffff8c4899c8 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock+0x50/0x140 lib/refcount.c:113

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (nbd_index_mutex){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:959 [inline]
       __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
       nbd_open+0x7d/0x8a0 drivers/block/nbd.c:1483
       blkdev_get_whole+0xa1/0x420 fs/block_dev.c:1253
       blkdev_get_by_dev.part.0+0x30c/0xdd0 fs/block_dev.c:1417
       blkdev_get_by_dev fs/block_dev.c:1506 [inline]
       blkdev_open+0x295/0x300 fs/block_dev.c:1512
       do_dentry_open+0x4c8/0x11d0 fs/open.c:826
       do_open fs/namei.c:3374 [inline]
       path_openat+0x1c23/0x27f0 fs/namei.c:3507
       do_filp_open+0x1aa/0x400 fs/namei.c:3534
       do_sys_openat2+0x16d/0x420 fs/open.c:1204
       do_sys_open fs/open.c:1220 [inline]
       __do_sys_open fs/open.c:1228 [inline]
       __se_sys_open fs/open.c:1224 [inline]
       __x64_sys_open+0x119/0x1c0 fs/open.c:1224
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (&disk->open_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3051 [inline]
       check_prevs_add kernel/locking/lockdep.c:3174 [inline]
       validate_chain kernel/locking/lockdep.c:3789 [inline]
       __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015
       lock_acquire kernel/locking/lockdep.c:5625 [inline]
       lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
       __mutex_lock_common kernel/locking/mutex.c:959 [inline]
       __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
       del_gendisk+0x8b/0x770 block/genhd.c:587
       nbd_dev_remove drivers/block/nbd.c:241 [inline]
       nbd_put.part.0+0x82/0x160 drivers/block/nbd.c:263
       nbd_put drivers/block/nbd.c:1913 [inline]
       nbd_genl_connect+0x1383/0x1820 drivers/block/nbd.c:2003
       genl_family_rcv_msg_doit+0x228/0x320 net/netlink/genetlink.c:739
       genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
       genl_rcv_msg+0x328/0x580 net/netlink/genetlink.c:800
       netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504
       genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
       netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
       netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1340
       netlink_sendmsg+0x86d/0xdb0 net/netlink/af_netlink.c:1929
       sock_sendmsg_nosec net/socket.c:703 [inline]
       sock_sendmsg+0xcf/0x120 net/socket.c:723
       ____sys_sendmsg+0x6e8/0x810 net/socket.c:2392
       ___sys_sendmsg+0xf3/0x170 net/socket.c:2446
       __sys_sendmsg+0xe5/0x1b0 net/socket.c:2475
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(nbd_index_mutex);
                               lock(&disk->open_mutex);
                               lock(nbd_index_mutex);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

3 locks held by syz-executor191/8426:
 #0: ffffffff8d160150 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40 net/netlink/genetlink.c:810
 #1: ffffffff8d160208 (genl_mutex){+.+.}-{3:3}, at: genl_lock net/netlink/genetlink.c:33 [inline]
 #1: ffffffff8d160208 (genl_mutex){+.+.}-{3:3}, at: genl_rcv_msg+0x3e0/0x580 net/netlink/genetlink.c:798
 #2: ffffffff8c4899c8 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock lib/refcount.c:118 [inline]
 #2: ffffffff8c4899c8 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock+0x50/0x140 lib/refcount.c:113

stack backtrace:
CPU: 1 PID: 8426 Comm: syz-executor191 Not tainted 5.14.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2131
 check_prev_add kernel/locking/lockdep.c:3051 [inline]
 check_prevs_add kernel/locking/lockdep.c:3174 [inline]
 validate_chain kernel/locking/lockdep.c:3789 [inline]
 __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015
 lock_acquire kernel/locking/lockdep.c:5625 [inline]
 lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
 __mutex_lock_common kernel/locking/mutex.c:959 [inline]
 __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
 del_gendisk+0x8b/0x770 block/genhd.c:587
 nbd_dev_remove drivers/block/nbd.c:241 [inline]
 nbd_put.part.0+0x82/0x160 drivers/block/nbd.c:263
 nbd_put drivers/block/nbd.c:1913 [inline]
 nbd_genl_connect+0x1383/0x1820 drivers/block/nbd.c:2003
 genl_family_rcv_msg_doit+0x228/0x320 net/netlink/genetlink.c:739
 genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
 genl_rcv_msg+0x328/0x580 net/netlink/genetlink.c:800
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1340
 netlink_sendmsg+0x86d/0xdb0 net/netlink/af_netlink.c:1929
 sock_sendmsg_nosec net/socket.c:703 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:723
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2392
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2446
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2475
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x440019
Code: 35 01 00 85 c0 b8 00 00 00 00 48 0f 44 c3 5b c3 90 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe55976f08 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000440019
RDX: 0000000002000800 RSI: 0000000020002580 RDI: 0000000000000003
RBP: 0000000000000008 R08: 0000000000000002 R09: 00007ffe55976f30
R10: 000000000000000c R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000008 R14: 0000000000000001 R15: 0000000000000008