[moderation] [cgroups?] KCSAN: data-race in css_set_move_task / memcpy_and_pad (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 24d479d26b25 Linux 6.19-rc6
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13769b9a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=676c6f0212d0c041
dashboard link: https://syzkaller.appspot.com/bug?extid=1ee8687806d5edebd5ad
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [cgr...@vger.kernel.org han...@cmpxchg.org linux-...@vger.kernel.org mko...@suse.com t...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e47d2b960e97/disk-24d479d2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/75c59e1fc76a/vmlinux-24d479d2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e42579adf478/bzImage-24d479d2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1ee868...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in css_set_move_task / memcpy_and_pad

write to 0xffff888102534b60 of 8 bytes by task 31 on cpu 1:
__list_del include/linux/list.h:203 [inline]
__list_del_entry include/linux/list.h:226 [inline]
list_del_init include/linux/list.h:295 [inline]
css_set_move_task+0x212/0x430 kernel/cgroup/cgroup.c:932
do_cgroup_task_dead kernel/cgroup/cgroup.c:6998 [inline]
cgroup_task_dead+0x6f/0x2b0 kernel/cgroup/cgroup.c:7062
finish_task_switch+0x1b1/0x280 kernel/sched/core.c:5156
context_switch kernel/sched/core.c:5263 [inline]
__schedule+0x82d/0xc90 kernel/sched/core.c:6867
__schedule_loop kernel/sched/core.c:6949 [inline]
schedule+0x5e/0xd0 kernel/sched/core.c:6964
do_wait+0x10e/0x240 kernel/exit.c:1721
kernel_wait+0x72/0x100 kernel/exit.c:1892
call_usermodehelper_exec_sync kernel/umh.c:136 [inline]
call_usermodehelper_exec_work+0x9c/0x160 kernel/umh.c:163
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
worker_thread+0x581/0x770 kernel/workqueue.c:3421
kthread+0x488/0x510 kernel/kthread.c:463
ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffff888102534200 of 3264 bytes by task 21831 on cpu 0:
memcpy_and_pad+0x48/0x80 lib/string_helpers.c:1007
arch_dup_task_struct+0x2c/0x40 arch/x86/kernel/process.c:108
dup_task_struct+0x6e/0x940 kernel/fork.c:919
copy_process+0x37e/0x1f10 kernel/fork.c:2052
kernel_clone+0x16b/0x5b0 kernel/fork.c:2651
__do_sys_clone kernel/fork.c:2792 [inline]
__se_sys_clone kernel/fork.c:2776 [inline]
__x64_sys_clone+0x143/0x180 kernel/fork.c:2776
x64_sys_call+0x12d0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:57
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 21831 Comm: dhcpcd-run-hook Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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