[moderation] [kernel?] KCSAN: data-race in pcpu_balance_workfn / pcpu_nr_pages (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 67a993863163 Merge tag 'v6.16-p6' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16bd708c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=39acdbb3c95d37e5
dashboard link: https://syzkaller.appspot.com/bug?extid=e5bd32b79413e86f389e
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [b...@alien8.de dave....@linux.intel.com h...@zytor.com linux-...@vger.kernel.org mi...@redhat.com tg...@linutronix.de x...@kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/351756923090/disk-67a99386.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f2762f676256/vmlinux-67a99386.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bc628869dc44/bzImage-67a99386.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e5bd32...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in pcpu_balance_workfn / pcpu_nr_pages

read-write to 0xffffffff88e84988 of 8 bytes by task 3391 on cpu 1:
pcpu_chunk_depopulated mm/percpu.c:1540 [inline]
pcpu_reclaim_populated mm/percpu.c:2152 [inline]
pcpu_balance_workfn+0x2eb/0xc00 mm/percpu.c:2204
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3321
worker_thread+0x582/0x770 kernel/workqueue.c:3402
kthread+0x486/0x510 kernel/kthread.c:464
ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff88e84988 of 8 bytes by task 12195 on cpu 0:
pcpu_nr_pages+0x16/0x40 mm/percpu.c:3358
meminfo_proc_show+0x94b/0xa30 fs/proc/meminfo.c:132
traverse+0x144/0x3a0 fs/seq_file.c:111
seq_read_iter+0x853/0x940 fs/seq_file.c:195
proc_reg_read_iter+0xe3/0x180 fs/proc/inode.c:295
io_iter_do_read io_uring/rw.c:828 [inline]
__io_read+0x438/0xc20 io_uring/rw.c:941
io_read+0x1c/0x60 io_uring/rw.c:1020
__io_issue_sqe+0xfe/0x2e0 io_uring/io_uring.c:1738
io_issue_sqe+0x53/0x970 io_uring/io_uring.c:1761
io_queue_sqe io_uring/io_uring.c:1968 [inline]
io_submit_sqe io_uring/io_uring.c:2224 [inline]
io_submit_sqes+0x667/0xfd0 io_uring/io_uring.c:2337
__do_sys_io_uring_enter io_uring/io_uring.c:3404 [inline]
__se_sys_io_uring_enter+0x1c1/0x1b70 io_uring/io_uring.c:3338
__x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:3338
x64_sys_call+0x28c8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:427
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000295 -> 0x000000000000028e

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 12195 Comm: syz.5.3624 Not tainted 6.16.0-rc3-syzkaller-00190-g67a993863163 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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