Message-ID: <6858b265.a00a0220.2e5631.0001.GAE@google.com>
Date: Sun, 22 Jun 2025 18:48:21 -0700
From: syzbot <syzbot+67ee62f1782c5d4e5d0c@...kaller.appspotmail.com>
To: bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, 
	linux-kernel@...r.kernel.org, mingo@...hat.com, 
	syzkaller-bugs@...glegroups.com, tglx@...utronix.de, x86@...nel.org
Subject: [syzbot] [kernel?] possible deadlock in worker_thread (2)

Hello,

syzbot found the following issue on:

HEAD commit:    74b4cc9b8780 Merge tag 'cgroup-for-6.16-rc2-fixes' of git:..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1008be82580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4130f4d8a06c3e71
dashboard link: https://syzkaller.appspot.com/bug?extid=67ee62f1782c5d4e5d0c
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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-74b4cc9b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/264068bc8f84/vmlinux-74b4cc9b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4f86c1c65991/bzImage-74b4cc9b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+67ee62f1782c5d4e5d0c@...kaller.appspotmail.com

block nbd12: Receive control failed (result -32)
======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc2-syzkaller-00071-g74b4cc9b8780 #0 Not tainted
------------------------------------------------------
kworker/u33:1/5298 is trying to acquire lock:
ffff888027fc7a30 (&nbd->config_lock){+.+.}-{4:4}, at: refcount_dec_and_mutex_lock+0x51/0xc0 lib/refcount.c:118

but task is already holding lock:
ffffc900270dfd10 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3214

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 ((work_completion)(&args->work)){+.+.}-{0:0}:
       process_one_work+0x932/0x1b70 kernel/workqueue.c:3214
       process_scheduled_works kernel/workqueue.c:3321 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
       kthread+0x3c2/0x780 kernel/kthread.c:464
       ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 ((wq_completion)nbd4-recv){+.+.}-{0:0}:
       touch_wq_lockdep_map+0xad/0x1c0 kernel/workqueue.c:3909
       __flush_workqueue+0x128/0x1230 kernel/workqueue.c:3951
       nbd_disconnect_and_put+0x9b/0x1c0 drivers/block/nbd.c:2242
       nbd_genl_disconnect+0x396/0x570 drivers/block/nbd.c:2281
       genl_family_rcv_msg_doit+0x206/0x2f0 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x55c/0x800 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2534
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
       netlink_unicast+0x53d/0x7f0 net/netlink/af_netlink.c:1339
       netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1883
       sock_sendmsg_nosec net/socket.c:712 [inline]
       __sock_sendmsg net/socket.c:727 [inline]
       ____sys_sendmsg+0xa95/0xc70 net/socket.c:2566
       ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620
       __sys_sendmsg+0x16d/0x220 net/socket.c:2652
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&nbd->config_lock){+.+.}-{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
       refcount_dec_and_mutex_lock+0x51/0xc0 lib/refcount.c:118
       nbd_config_put+0x31/0x750 drivers/block/nbd.c:1423
       recv_work+0x681/0xa80 drivers/block/nbd.c:1021
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
       process_scheduled_works kernel/workqueue.c:3321 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
       kthread+0x3c2/0x780 kernel/kthread.c:464
       ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  &nbd->config_lock --> (wq_completion)nbd4-recv --> (work_completion)(&args->work)

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock((work_completion)(&args->work));
                               lock((wq_completion)nbd4-recv);
                               lock((work_completion)(&args->work));
  lock(&nbd->config_lock);

 *** DEADLOCK ***

2 locks held by kworker/u33:1/5298:
 #0: ffff8880280bb148 ((wq_completion)nbd12-recv){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3213
 #1: ffffc900270dfd10 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3214

stack backtrace:
CPU: 2 UID: 0 PID: 5298 Comm: kworker/u33:1 Not tainted 6.16.0-rc2-syzkaller-00071-g74b4cc9b8780 #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
Workqueue: nbd12-recv recv_work
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
 refcount_dec_and_mutex_lock+0x51/0xc0 lib/refcount.c:118
 nbd_config_put+0x31/0x750 drivers/block/nbd.c:1423
 recv_work+0x681/0xa80 drivers/block/nbd.c:1021
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
block nbd12: shutting down sockets
==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: slab-use-after-free in atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline]
BUG: KASAN: slab-use-after-free in recv_work+0x694/0xa80 drivers/block/nbd.c:1022
Write of size 4 at addr ffff8880549ba078 by task kworker/u33:1/5298

CPU: 0 UID: 0 PID: 5298 Comm: kworker/u33:1 Not tainted 6.16.0-rc2-syzkaller-00071-g74b4cc9b8780 #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
Workqueue: nbd12-recv recv_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xcd/0x680 mm/kasan/report.c:521
 kasan_report+0xe0/0x110 mm/kasan/report.c:634
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline]
 recv_work+0x694/0xa80 drivers/block/nbd.c:1022
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Allocated by task 10333:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394
 kmalloc_noprof include/linux/slab.h:905 [inline]
 kzalloc_noprof include/linux/slab.h:1039 [inline]
 nbd_alloc_and_init_config+0x97/0x2a0 drivers/block/nbd.c:1659
 nbd_genl_connect+0x490/0x1c20 drivers/block/nbd.c:2121
 genl_family_rcv_msg_doit+0x206/0x2f0 net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x55c/0x800 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2534
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x53d/0x7f0 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg net/socket.c:727 [inline]
 ____sys_sendmsg+0xa95/0xc70 net/socket.c:2566
 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620
 __sys_sendmsg+0x16d/0x220 net/socket.c:2652
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5298:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x51/0x70 mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2381 [inline]
 slab_free mm/slub.c:4643 [inline]
 kfree+0x2b4/0x4d0 mm/slub.c:4842
 nbd_config_put+0x3c1/0x750 drivers/block/nbd.c:1449
 recv_work+0x681/0xa80 drivers/block/nbd.c:1021
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff8880549ba000
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 120 bytes inside of
 freed 256-byte region [ffff8880549ba000, ffff8880549ba100)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x549ba
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b842b40 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b842b40 0000000000000000 dead000000000001
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffea0001526e81 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 8542, tgid 8542 (syz-executor), ts 169523608298, free_ts 169387762780
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1704
 prep_new_page mm/page_alloc.c:1712 [inline]
 get_page_from_freelist+0x1321/0x3890 mm/page_alloc.c:3669
 __alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:4959
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2419
 alloc_slab_page mm/slub.c:2451 [inline]
 allocate_slab mm/slub.c:2619 [inline]
 new_slab+0x23b/0x330 mm/slub.c:2673
 ___slab_alloc+0xd9c/0x1940 mm/slub.c:3859
 __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3949
 __slab_alloc_node mm/slub.c:4024 [inline]
 slab_alloc_node mm/slub.c:4185 [inline]
 __do_kmalloc_node mm/slub.c:4327 [inline]
 __kmalloc_noprof+0x2f2/0x510 mm/slub.c:4340
 kmalloc_noprof include/linux/slab.h:909 [inline]
 kmalloc_array_noprof include/linux/slab.h:948 [inline]
 security_inode_init_security+0x13f/0x390 security/security.c:1829
 shmem_symlink+0x135/0x9f0 mm/shmem.c:4098
 vfs_symlink fs/namei.c:4739 [inline]
 vfs_symlink+0x403/0x680 fs/namei.c:4723
 do_symlinkat+0x261/0x310 fs/namei.c:4765
 __do_sys_symlinkat fs/namei.c:4781 [inline]
 __se_sys_symlinkat fs/namei.c:4778 [inline]
 __x64_sys_symlinkat+0x93/0xc0 fs/namei.c:4778
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 8529 tgid 8529 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1248 [inline]
 __free_frozen_pages+0x7fe/0x1180 mm/page_alloc.c:2706
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x4d/0x120 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4148 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 kmem_cache_alloc_noprof+0x1cb/0x3b0 mm/slub.c:4204
 getname_flags.part.0+0x4c/0x550 fs/namei.c:146
 getname_flags include/linux/audit.h:322 [inline]
 getname include/linux/fs.h:2907 [inline]
 __do_sys_unlink fs/namei.c:4705 [inline]
 __se_sys_unlink fs/namei.c:4703 [inline]
 __x64_sys_unlink+0xb0/0x110 fs/namei.c:4703
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff8880549b9f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880549b9f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880549ba000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff8880549ba080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880549ba100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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