======================================================
WARNING: possible circular locking dependency detected
5.13.0-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor385/8453 is trying to acquire lock:
ffff88801f052d18 (&disk->open_mutex){+.+.}-{3:3}, at: del_gendisk+0x8b/0x770 block/genhd.c:587

but task is already holding lock:
ffffffff8cc7cb68 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock lib/refcount.c:118 [inline]
ffffffff8cc7cb68 (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:1456
       blkdev_get_whole+0xa1/0x420 fs/block_dev.c:1251
       blkdev_get_by_dev.part.0+0x30c/0xdd0 fs/block_dev.c:1415
       blkdev_get_by_dev fs/block_dev.c:1504 [inline]
       blkdev_open+0x295/0x300 fs/block_dev.c:1510
       do_dentry_open+0x4c8/0x11c0 fs/open.c:826
       do_open fs/namei.c:3361 [inline]
       path_openat+0x1c0e/0x27e0 fs/namei.c:3494
       do_filp_open+0x190/0x3d0 fs/namei.c:3521
       do_sys_openat2+0x16d/0x420 fs/open.c:1195
       do_sys_open fs/open.c:1211 [inline]
       __do_sys_open fs/open.c:1219 [inline]
       __se_sys_open fs/open.c:1215 [inline]
       __x64_sys_open+0x119/0x1c0 fs/open.c:1215
       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:224 [inline]
       nbd_put.part.0+0x82/0x160 drivers/block/nbd.c:246
       nbd_put drivers/block/nbd.c:1903 [inline]
       nbd_genl_connect+0x1214/0x1660 drivers/block/nbd.c:1957
       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+0x85b/0xda0 net/netlink/af_netlink.c:1929
       sock_sendmsg_nosec net/socket.c:702 [inline]
       sock_sendmsg+0xcf/0x120 net/socket.c:722
       ____sys_sendmsg+0x6e8/0x810 net/socket.c:2385
       ___sys_sendmsg+0xf3/0x170 net/socket.c:2439
       __sys_sendmsg+0xe5/0x1b0 net/socket.c:2468
       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-executor385/8453:
 #0: ffffffff8d94a490 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40 net/netlink/genetlink.c:810
 #1: ffffffff8d94a548 (genl_mutex){+.+.}-{3:3}, at: genl_lock net/netlink/genetlink.c:33 [inline]
 #1: ffffffff8d94a548 (genl_mutex){+.+.}-{3:3}, at: genl_rcv_msg+0x3e0/0x580 net/netlink/genetlink.c:798
 #2: ffffffff8cc7cb68 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock lib/refcount.c:118 [inline]
 #2: ffffffff8cc7cb68 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock+0x50/0x140 lib/refcount.c:113

stack backtrace:
CPU: 0 PID: 8453 Comm: syz-executor385 Not tainted 5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:96
 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:224 [inline]
 nbd_put.part.0+0x82/0x160 drivers/block/nbd.c:246
 nbd_put drivers/block/nbd.c:1903 [inline]
 nbd_genl_connect+0x1214/0x1660 drivers/block/nbd.c:1957
 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+0x85b/0xda0 net/netlink/af_netlink.c:1929
 sock_sendmsg_nosec net/socket.c:702 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:722
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2385
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2439
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2468
 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: 0033:0x43fa89
Code: 28 c3 e8 5a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffa3b11d18 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004004a0 RCX: 000000000043fa89
RDX: 0000000000000000 RSI: 0000000020001880 RDI: 0000000000000004
RBP: 00000000004034f0 R08: 0000000000000004 R09: 00000000004004a0
R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000403580
R13: 0000000000000000 R14: 00000000004ad018 R15: 00000000004004a0
general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 PID: 8453 Comm: syz-executor385 Not tainted 5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:blk_mq_map_queue_type block/blk-mq.h:96 [inline]
RIP: 0010:blk_mq_get_sq_hctx block/blk-mq.c:1663 [inline]
RIP: 0010:blk_mq_run_hw_queues+0x32b/0x4a0 block/blk-mq.c:1682
Code: ea 48 c1 ea 03 80 3c 02 00 0f 85 51 01 00 00 48 8b 45 00 89 db 48 8d 1c 98 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 <0f> b6 14 02 48 89 d8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 ed
RSP: 0018:ffffc9000169f3b0 EFLAGS: 00010247
RAX: dffffc0000000000 RBX: 0000000000000004 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff83be8009 RDI: ffff8881460cb4c0
RBP: ffff88801f426000 R08: 0000000000000000 R09: ffff8881460cb437
R10: ffffffff83be7e41 R11: 0000000000000000 R12: ffff8881460caaf0
R13: ffff8881460d5f00 R14: ffff8880168c3808 R15: 0000000000000001
FS:  00000000008a3300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005564442c0928 CR3: 0000000036ecc000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 blk_freeze_queue_start+0xc4/0xe0 block/blk-mq.c:142
 blk_set_queue_dying+0x24/0x80 block/blk-core.c:353
 blk_cleanup_queue+0x7b/0x1e0 block/blk-core.c:380
 blk_cleanup_disk+0x33/0x80 block/genhd.c:1324
 nbd_dev_remove drivers/block/nbd.c:226 [inline]
 nbd_put.part.0+0x92/0x160 drivers/block/nbd.c:246
 nbd_put drivers/block/nbd.c:1903 [inline]
 nbd_genl_connect+0x1214/0x1660 drivers/block/nbd.c:1957
 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+0x85b/0xda0 net/netlink/af_netlink.c:1929
 sock_sendmsg_nosec net/socket.c:702 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:722
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2385
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2439
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2468
 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: 0033:0x43fa89
Code: 28 c3 e8 5a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffa3b11d18 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004004a0 RCX: 000000000043fa89
RDX: 0000000000000000 RSI: 0000000020001880 RDI: 0000000000000004
RBP: 00000000004034f0 R08: 0000000000000004 R09: 00000000004004a0
R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000403580
R13: 0000000000000000 R14: 00000000004ad018 R15: 00000000004004a0
Modules linked in:
---[ end trace 5901d46f06584e8e ]---
RIP: 0010:blk_mq_map_queue_type block/blk-mq.h:96 [inline]
RIP: 0010:blk_mq_get_sq_hctx block/blk-mq.c:1663 [inline]
RIP: 0010:blk_mq_run_hw_queues+0x32b/0x4a0 block/blk-mq.c:1682
Code: ea 48 c1 ea 03 80 3c 02 00 0f 85 51 01 00 00 48 8b 45 00 89 db 48 8d 1c 98 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 <0f> b6 14 02 48 89 d8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 ed
RSP: 0018:ffffc9000169f3b0 EFLAGS: 00010247
RAX: dffffc0000000000 RBX: 0000000000000004 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff83be8009 RDI: ffff8881460cb4c0
RBP: ffff88801f426000 R08: 0000000000000000 R09: ffff8881460cb437
R10: ffffffff83be7e41 R11: 0000000000000000 R12: ffff8881460caaf0
R13: ffff8881460d5f00 R14: ffff8880168c3808 R15: 0000000000000001
FS:  00000000008a3300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff95803e0a8 CR3: 0000000036ecc000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400