* [syzbot] [cgroups?] possible deadlock in copy_process
@ 2026-03-26 9:48 syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-03-26 9:48 UTC (permalink / raw)
To: cgroups, hannes, linux-kernel, mkoutny, syzkaller-bugs, tj
Hello,
syzbot found the following issue on:
HEAD commit: 785f0eb2f85d Add linux-next specific files for 20260320
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=105e2a06580000
kernel config: https://syzkaller.appspot.com/x/.config?x=22bf3527036b9be1
dashboard link: https://syzkaller.appspot.com/bug?extid=327400a7d1255e319efb
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2e684d8ea98b/disk-785f0eb2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b33fd1111047/vmlinux-785f0eb2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2c5ee1287187/bzImage-785f0eb2.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+327400a7d1255e319efb@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.9.3615/18333 is trying to acquire lock:
ffffffff8ea843c0 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:317 [inline]
ffffffff8ea843c0 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4520 [inline]
ffffffff8ea843c0 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4875 [inline]
ffffffff8ea843c0 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_lru_noprof+0x45/0x640 mm/slub.c:4917
but task is already holding lock:
ffffffff8e99cfd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x2a1a/0x4430 kernel/fork.c:2375
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #7 (cgroup_threadgroup_rwsem){++++}-{0:0}:
percpu_down_write+0x54/0x320 kernel/locking/percpu-rwsem.c:232
cgroup_attach_lock kernel/cgroup/cgroup.c:2484 [inline]
cgroup_procs_write_start+0x574/0x900 kernel/cgroup/cgroup.c:3043
__cgroup_procs_write+0x9b/0x300 kernel/cgroup/cgroup.c:5326
cgroup_procs_write+0x27/0x50 kernel/cgroup/cgroup.c:5361
cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4249
kernfs_fop_write_iter+0x3af/0x540 fs/kernfs/file.c:352
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x61d/0xb90 fs/read_write.c:688
ksys_write+0x150/0x270 fs/read_write.c:740
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #6 (cpu_hotplug_lock){++++}-{0:0}:
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
cpus_read_lock+0x42/0x160 kernel/cpu.c:490
static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
nbd_reconnect_socket drivers/block/nbd.c:1342 [inline]
nbd_genl_reconfigure+0x132f/0x1ea0 drivers/block/nbd.c:2431
genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x80f/0x9b0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec+0x112/0x150 net/socket.c:796
__sock_sendmsg net/socket.c:811 [inline]
____sys_sendmsg+0x589/0x8c0 net/socket.c:2668
___sys_sendmsg+0x2a5/0x360 net/socket.c:2722
__sys_sendmsg net/socket.c:2754 [inline]
__do_sys_sendmsg net/socket.c:2759 [inline]
__se_sys_sendmsg net/socket.c:2757 [inline]
__x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2757
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:632 [inline]
__mutex_lock+0x19e/0x1420 kernel/locking/mutex.c:794
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x37b/0x1100 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0xa70/0x1910 block/blk-mq.c:2148
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
__blk_mq_sched_dispatch_requests+0xdcc/0x1600 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2386
blk_mq_dispatch_list+0xd16/0xe10 include/linux/spinlock.h:-1
blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
__blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x28d/0x580 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:753
submit_bh fs/buffer.c:2842 [inline]
block_read_full_folio+0x599/0x830 fs/buffer.c:2444
filemap_read_folio+0x137/0x3b0 mm/filemap.c:2502
do_read_cache_folio+0x358/0x590 mm/filemap.c:4107
read_mapping_folio include/linux/pagemap.h:1028 [inline]
read_part_sector+0xb6/0x2b0 block/partitions/core.c:723
adfspart_check_ICS+0xa5/0xa40 block/partitions/acorn.c:360
check_partition block/partitions/core.c:142 [inline]
blk_add_partitions block/partitions/core.c:590 [inline]
bdev_disk_changed+0x7ba/0x1550 block/partitions/core.c:694
blkdev_get_whole+0x380/0x510 block/bdev.c:764
bdev_open+0x31e/0xd30 block/bdev.c:973
blkdev_open+0x470/0x610 block/fops.c:697
do_dentry_open+0x785/0x14e0 fs/open.c:949
vfs_open+0x3b/0x340 fs/open.c:1081
do_open fs/namei.c:4693 [inline]
path_openat+0x2e08/0x3860 fs/namei.c:4852
do_file_open+0x23e/0x4a0 fs/namei.c:4881
do_sys_openat2+0x113/0x200 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #4 (&cmd->lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:632 [inline]
__mutex_lock+0x19e/0x1420 kernel/locking/mutex.c:794
nbd_queue_rq+0xc6/0x1100 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0xa70/0x1910 block/blk-mq.c:2148
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
__blk_mq_sched_dispatch_requests+0xdcc/0x1600 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2386
blk_mq_dispatch_list+0xd16/0xe10 include/linux/spinlock.h:-1
blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
__blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x28d/0x580 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:753
submit_bh fs/buffer.c:2842 [inline]
block_read_full_folio+0x599/0x830 fs/buffer.c:2444
filemap_read_folio+0x137/0x3b0 mm/filemap.c:2502
do_read_cache_folio+0x358/0x590 mm/filemap.c:4107
read_mapping_folio include/linux/pagemap.h:1028 [inline]
read_part_sector+0xb6/0x2b0 block/partitions/core.c:723
adfspart_check_ICS+0xa5/0xa40 block/partitions/acorn.c:360
check_partition block/partitions/core.c:142 [inline]
blk_add_partitions block/partitions/core.c:590 [inline]
bdev_disk_changed+0x7ba/0x1550 block/partitions/core.c:694
blkdev_get_whole+0x380/0x510 block/bdev.c:764
bdev_open+0x31e/0xd30 block/bdev.c:973
blkdev_open+0x470/0x610 block/fops.c:697
do_dentry_open+0x785/0x14e0 fs/open.c:949
vfs_open+0x3b/0x340 fs/open.c:1081
do_open fs/namei.c:4693 [inline]
path_openat+0x2e08/0x3860 fs/namei.c:4852
do_file_open+0x23e/0x4a0 fs/namei.c:4881
do_sys_openat2+0x113/0x200 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #3 (set->srcu){.+.+}-{0:0}:
srcu_lock_sync include/linux/srcu.h:199 [inline]
__synchronize_srcu+0xca/0x3e0 kernel/rcu/srcutree.c:1505
elevator_switch+0x1e8/0x7a0 block/elevator.c:576
elevator_change+0x2cc/0x450 block/elevator.c:681
elevator_set_default+0x36c/0x430 block/elevator.c:754
blk_register_queue+0x3e9/0x4e0 block/blk-sysfs.c:987
__add_disk+0x677/0xd50 block/genhd.c:528
add_disk_fwnode+0xfb/0x480 block/genhd.c:597
add_disk include/linux/blkdev.h:793 [inline]
nbd_dev_add+0x72c/0xb50 drivers/block/nbd.c:1984
nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
do_one_initcall+0x250/0x870 init/main.c:1386
do_initcall_level+0x104/0x190 init/main.c:1448
do_initcalls+0x59/0xa0 init/main.c:1464
kernel_init_freeable+0x2a6/0x3e0 init/main.c:1696
kernel_init+0x1d/0x1d0 init/main.c:1586
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #2 (&q->elevator_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:632 [inline]
__mutex_lock+0x19e/0x1420 kernel/locking/mutex.c:794
elevator_change+0x1b3/0x450 block/elevator.c:679
elevator_set_none+0xb5/0x140 block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5131 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5176 [inline]
blk_mq_update_nr_hw_queues+0x5e7/0x1a60 block/blk-mq.c:5241
nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489
nbd_genl_connect+0x165b/0x1cf0 drivers/block/nbd.c:2239
genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x80f/0x9b0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec+0x112/0x150 net/socket.c:796
__sock_sendmsg net/socket.c:811 [inline]
____sys_sendmsg+0x589/0x8c0 net/socket.c:2668
___sys_sendmsg+0x2a5/0x360 net/socket.c:2722
__sys_sendmsg net/socket.c:2754 [inline]
__do_sys_sendmsg net/socket.c:2759 [inline]
__se_sys_sendmsg net/socket.c:2757 [inline]
__x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2757
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (&q->q_usage_counter(io)#49){++++}-{0:0}:
blk_alloc_queue+0x546/0x680 block/blk-core.c:461
blk_mq_alloc_queue block/blk-mq.c:4450 [inline]
__blk_mq_alloc_disk+0x197/0x390 block/blk-mq.c:4497
nbd_dev_add+0x499/0xb50 drivers/block/nbd.c:1954
nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
do_one_initcall+0x250/0x870 init/main.c:1386
do_initcall_level+0x104/0x190 init/main.c:1448
do_initcalls+0x59/0xa0 init/main.c:1464
kernel_init_freeable+0x2a6/0x3e0 init/main.c:1696
kernel_init+0x1d/0x1d0 init/main.c:1586
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #0 (fs_reclaim){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__fs_reclaim_acquire mm/page_alloc.c:4312 [inline]
fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4326
might_alloc include/linux/sched/mm.h:317 [inline]
slab_pre_alloc_hook mm/slub.c:4520 [inline]
slab_alloc_node mm/slub.c:4875 [inline]
kmem_cache_alloc_lru_noprof+0x45/0x640 mm/slub.c:4917
alloc_inode+0xb8/0x1b0 fs/inode.c:349
iget_locked+0x131/0x6a0 fs/inode.c:1480
kernfs_get_inode+0x4f/0x780 fs/kernfs/inode.c:252
cgroup_may_write kernel/cgroup/cgroup.c:5252 [inline]
cgroup_css_set_fork kernel/cgroup/cgroup.c:6693 [inline]
cgroup_can_fork+0xaf9/0xe70 kernel/cgroup/cgroup.c:6783
copy_process+0x2a1a/0x4430 kernel/fork.c:2375
kernel_clone+0x26d/0x8e0 kernel/fork.c:2720
__do_sys_clone3 kernel/fork.c:3021 [inline]
__se_sys_clone3+0x33c/0x360 kernel/fork.c:3000
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
fs_reclaim --> cpu_hotplug_lock --> cgroup_threadgroup_rwsem
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
rlock(cgroup_threadgroup_rwsem);
lock(cpu_hotplug_lock);
lock(cgroup_threadgroup_rwsem);
lock(fs_reclaim);
*** DEADLOCK ***
2 locks held by syz.9.3615/18333:
#0: ffffffff8e99cd20 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_lock include/linux/cgroup.h:455 [inline]
#0: ffffffff8e99cd20 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_css_set_fork kernel/cgroup/cgroup.c:6651 [inline]
#0: ffffffff8e99cd20 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_can_fork+0x7c/0xe70 kernel/cgroup/cgroup.c:6783
#1: ffffffff8e99cfd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x2a1a/0x4430 kernel/fork.c:2375
stack backtrace:
CPU: 1 UID: 0 PID: 18333 Comm: syz.9.3615 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__fs_reclaim_acquire mm/page_alloc.c:4312 [inline]
fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4326
might_alloc include/linux/sched/mm.h:317 [inline]
slab_pre_alloc_hook mm/slub.c:4520 [inline]
slab_alloc_node mm/slub.c:4875 [inline]
kmem_cache_alloc_lru_noprof+0x45/0x640 mm/slub.c:4917
alloc_inode+0xb8/0x1b0 fs/inode.c:349
iget_locked+0x131/0x6a0 fs/inode.c:1480
kernfs_get_inode+0x4f/0x780 fs/kernfs/inode.c:252
cgroup_may_write kernel/cgroup/cgroup.c:5252 [inline]
cgroup_css_set_fork kernel/cgroup/cgroup.c:6693 [inline]
cgroup_can_fork+0xaf9/0xe70 kernel/cgroup/cgroup.c:6783
copy_process+0x2a1a/0x4430 kernel/fork.c:2375
kernel_clone+0x26d/0x8e0 kernel/fork.c:2720
__do_sys_clone3 kernel/fork.c:3021 [inline]
__se_sys_clone3+0x33c/0x360 kernel/fork.c:3000
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f49a759c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f49a8387ef8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b3
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f49a759c799
RDX: 00007f49a8387f10 RSI: 0000000000000058 RDI: 00007f49a8387f10
RBP: 00007f49a7632c99 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f49a7816038 R14: 00007f49a7815fa0 R15: 00007fff59f21a58
</TASK>
---
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2026-03-26 9:48 [syzbot] [cgroups?] possible deadlock in copy_process syzbot
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