linux-kernel - Re: [syzbot] [block?] possible deadlock in __del

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Message-ID: <688e9c6d.050a0220.3627e7.0000.GAE@google.com>
Date: Sat, 02 Aug 2025 16:17:01 -0700
From: syzbot <syzbot+2e9e529ac0b319316453@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	ujwal.kundur@...il.com
Subject: Re: [syzbot] [block?] possible deadlock in __del_gendisk

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: MAX_LOCKDEP_KEYS too low!

BUG: MAX_LOCKDEP_KEYS too low!
turning off the locking correctness validator.
CPU: 0 UID: 0 PID: 17006 Comm: syz.0.1967 Not tainted 6.16.0-syzkaller-g186f3edfdd41-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 register_lock_class+0x2e8/0x320 kernel/locking/lockdep.c:1332
 __lock_acquire+0x99/0xd20 kernel/locking/lockdep.c:5112
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 blk_freeze_acquire_lock block/blk.h:738 [inline]
 blk_freeze_queue_start block/blk-mq.c:184 [inline]
 blk_mq_freeze_queue_nomemsave+0xd5/0x120 block/blk-mq.c:205
 blk_mq_freeze_queue include/linux/blk-mq.h:934 [inline]
 elevator_change+0xd5/0x320 block/elevator.c:666
 elevator_set_default+0x186/0x260 block/elevator.c:742
 blk_register_queue+0x35d/0x400 block/blk-sysfs.c:905
 __add_disk+0x677/0xd50 block/genhd.c:528
 add_disk_fwnode+0xfc/0x480 block/genhd.c:597
 add_disk include/linux/blkdev.h:773 [inline]
 nbd_dev_add+0x717/0xae0 drivers/block/nbd.c:1973
 nbd_genl_connect+0x919/0x18f0 drivers/block/nbd.c:2114
 genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
 ____sys_sendmsg+0x505/0x830 net/socket.c:2614
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
 __sys_sendmsg net/socket.c:2700 [inline]
 __do_sys_sendmsg net/socket.c:2705 [inline]
 __se_sys_sendmsg net/socket.c:2703 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe578b8e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe579a4d038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fe578db5fa0 RCX: 00007fe578b8e929
RDX: 0000000020000000 RSI: 0000200000001ac0 RDI: 0000000000000004
RBP: 00007fe578c10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fe578db5fa0 R15: 00007ffe9f356178
 </TASK>


Tested on:

commit:         186f3edf Merge tag 'pinctrl-v6.17-1' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10ea7f82580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=18eb6d916c138763
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9e529ac0b319316453
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10eddcf0580000