[moderation] [cgroups?] KCSAN: data-race in css_set_move_task / memcpy_and_pad (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0e35b9b6ec0f Merge tag 'mm-hotfixes-stable-2026-07-06-17-4..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=156a2589580000
kernel config: https://syzkaller.appspot.com/x/.config?x=84b3039e8461eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=2d033bf8519b4b95dbb7
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
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/50ec388edb4b/disk-0e35b9b6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d5fde077ecdc/vmlinux-0e35b9b6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e0545f5d0fb1/bzImage-0e35b9b6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2d033b...@syzkaller.appspotmail.com

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

write to 0xffff888101dde018 of 8 bytes by task 22 on cpu 1:
__list_del include/linux/list.h:226 [inline]
__list_del_entry include/linux/list.h:249 [inline]
list_del_init include/linux/list.h:318 [inline]
css_set_move_task+0x1c1/0x380 kernel/cgroup/cgroup.c:909
do_cgroup_task_dead kernel/cgroup/cgroup.c:7076 [inline]
cgroup_task_dead+0x6f/0x2b0 kernel/cgroup/cgroup.c:7140
finish_task_switch+0x26e/0x340 kernel/sched/core.c:5405
context_switch kernel/sched/core.c:5513 [inline]
__schedule+0x799/0xd10 kernel/sched/core.c:7234
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0x5a/0xa0 kernel/sched/core.c:7326
smpboot_thread_fn+0x36f/0x510 kernel/smpboot.c:156
kthread+0x221/0x270 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff888101ddd640 of 3456 bytes by task 9328 on cpu 0:
memcpy_and_pad+0x48/0x80 lib/string_helpers.c:1008
arch_dup_task_struct+0x2c/0x40 arch/x86/kernel/process.c:108
dup_task_struct+0x6d/0x6a0 kernel/fork.c:925
copy_process+0x5a0/0x2310 kernel/fork.c:2115
kernel_clone+0x1c0/0x5f0 kernel/fork.c:2748
__do_sys_clone kernel/fork.c:2889 [inline]
__se_sys_clone kernel/fork.c:2873 [inline]
__x64_sys_clone+0x143/0x180 kernel/fork.c:2873
x64_sys_call+0x1222/0x3020 arch/x86/include/generated/asm/syscalls_64.h:57
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 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: 9328 Comm: dhcpcd-run-hook Tainted: G W syzkaller #0 PREEMPT(lazy)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


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