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Message-ID: <688ad18b.a00a0220.26d0e1.0033.GAE@google.com>
Date: Wed, 30 Jul 2025 19:14:35 -0700
From: syzbot <syzbot+aea0dfef449ccf91636b@...kaller.appspotmail.com>
To: axboe@...nel.dk, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
syzkaller-bugs@...glegroups.com
Subject: [syzbot] [block?] possible deadlock in del_gendisk (2)
Hello,
syzbot found the following issue on:
HEAD commit: 302f88ff3584 Merge tag 'for-linus' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=152528a2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=27aea6dad68e0c0c
dashboard link: https://syzkaller.appspot.com/bug?extid=aea0dfef449ccf91636b
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: i386
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-302f88ff.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b375ab423051/vmlinux-302f88ff.xz
kernel image: https://storage.googleapis.com/syzbot-assets/133b9f21ac36/bzImage-302f88ff.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aea0dfef449ccf91636b@...kaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc7-syzkaller-00127-g302f88ff3584 #0 Not tainted
------------------------------------------------------
syz.7.6877/31320 is trying to acquire lock:
but task is already holding lock:
ffff8880417fe368 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0x136/0x1e0 block/genhd.c:822
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&set->update_nr_hwq_lock){++++}-{4:4}:
down_write+0x92/0x200 kernel/locking/rwsem.c:1577
blk_mq_update_nr_hw_queues+0x32/0xcb0 block/blk-mq.c:5041
nbd_start_device+0x172/0xcd0 drivers/block/nbd.c:1476
nbd_start_device_ioctl drivers/block/nbd.c:1527 [inline]
__nbd_ioctl drivers/block/nbd.c:1602 [inline]
nbd_ioctl+0x219/0xda0 drivers/block/nbd.c:1642
compat_blkdev_ioctl+0x2eb/0x7a0 block/ioctl.c:760
__do_compat_sys_ioctl fs/ioctl.c:1005 [inline]
__se_compat_sys_ioctl fs/ioctl.c:948 [inline]
__ia32_compat_sys_ioctl+0x23f/0x370 fs/ioctl.c:948
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
__do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
-> #1 (&nbd->config_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:602 [inline]
__mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
refcount_dec_and_mutex_lock+0x51/0xc0 lib/refcount.c:118
nbd_config_put+0x31/0x750 drivers/block/nbd.c:1423
nbd_release+0xb7/0x190 drivers/block/nbd.c:1735
blkdev_put_whole+0xb0/0xf0 block/bdev.c:721
bdev_release+0x47e/0x6d0 block/bdev.c:1144
blkdev_release+0x15/0x20 block/fops.c:684
__fput+0x402/0xb70 fs/file_table.c:465
fput_close_sync+0x118/0x260 fs/file_table.c:570
__do_sys_close fs/open.c:1589 [inline]
__se_sys_close fs/open.c:1574 [inline]
__x64_sys_close+0x8b/0x120 fs/open.c:1574
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&disk->open_mutex){+.+.}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3168 [inline]
check_prevs_add kernel/locking/lockdep.c:3287 [inline]
validate_chain kernel/locking/lockdep.c:3911 [inline]
__lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
lock_acquire kernel/locking/lockdep.c:5871 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
__mutex_lock_common kernel/locking/mutex.c:602 [inline]
__mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
__del_gendisk+0xf5/0xbd0 block/genhd.c:710
del_gendisk+0x13e/0x1e0 block/genhd.c:823
loop_remove drivers/block/loop.c:2083 [inline]
loop_control_remove drivers/block/loop.c:2142 [inline]
loop_control_ioctl+0x4f1/0x630 drivers/block/loop.c:2180
__do_compat_sys_ioctl fs/ioctl.c:1005 [inline]
__se_compat_sys_ioctl fs/ioctl.c:948 [inline]
__ia32_compat_sys_ioctl+0x23f/0x370 fs/ioctl.c:948
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
__do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
other info that might help us debug this:
Chain exists of:
&disk->open_mutex --> &nbd->config_lock --> &set->update_nr_hwq_lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
rlock(&set->update_nr_hwq_lock);
lock(&nbd->config_lock);
lock(&set->update_nr_hwq_lock);
lock(&disk->open_mutex);
*** DEADLOCK ***
1 lock held by syz.7.6877/31320:
#0: ffff8880417fe368 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0x136/0x1e0 block/genhd.c:822
stack backtrace:
CPU: 0 UID: 0 PID: 31320 Comm: syz.7.6877 Not tainted 6.16.0-rc7-syzkaller-00127-g302f88ff3584 #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2046
check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2178
check_prev_add kernel/locking/lockdep.c:3168 [inline]
check_prevs_add kernel/locking/lockdep.c:3287 [inline]
validate_chain kernel/locking/lockdep.c:3911 [inline]
__lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
lock_acquire kernel/locking/lockdep.c:5871 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
__mutex_lock_common kernel/locking/mutex.c:602 [inline]
__mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
__del_gendisk+0xf5/0xbd0 block/genhd.c:710
del_gendisk+0x13e/0x1e0 block/genhd.c:823
loop_remove drivers/block/loop.c:2083 [inline]
loop_control_remove drivers/block/loop.c:2142 [inline]
loop_control_ioctl+0x4f1/0x630 drivers/block/loop.c:2180
__do_compat_sys_ioctl fs/ioctl.c:1005 [inline]
__se_compat_sys_ioctl fs/ioctl.c:948 [inline]
__ia32_compat_sys_ioctl+0x23f/0x370 fs/ioctl.c:948
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
__do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf70be579
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 0000000000004c81
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
----------------
Code disassembly (best guess), 2 bytes skipped:
0: 10 06 adc %al,(%rsi)
2: 03 74 b4 01 add 0x1(%rsp,%rsi,4),%esi
6: 10 07 adc %al,(%rdi)
8: 03 74 b0 01 add 0x1(%rax,%rsi,4),%esi
c: 10 08 adc %cl,(%rax)
e: 03 74 d8 01 add 0x1(%rax,%rbx,8),%esi
1e: 00 51 52 add %dl,0x52(%rcx)
21: 55 push %rbp
22: 89 e5 mov %esp,%ebp
24: 0f 34 sysenter
26: cd 80 int $0x80
* 28: 5d pop %rbp <-- trapping instruction
29: 5a pop %rdx
2a: 59 pop %rcx
2b: c3 ret
2c: 90 nop
2d: 90 nop
2e: 90 nop
2f: 90 nop
30: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi
37: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi
---
This report 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 syzkaller@...glegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
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