[moderation] [kernel?] KCSAN: data-race in __hrtimer_rearm_deferred / print_cpu

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 45dcf5e28813 Merge tag 'pcmcia-7.1-rc1' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16007702580000
kernel config: https://syzkaller.appspot.com/x/.config?x=deef952e1303dd49
dashboard link: https://syzkaller.appspot.com/bug?extid=20790177528defde1ce2
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [anna-...@linutronix.de fred...@kernel.org linux-...@vger.kernel.org tg...@kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2d64f39b45da/disk-45dcf5e2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4d8c88b63e56/vmlinux-45dcf5e2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dfd8c4613684/bzImage-45dcf5e2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+207901...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __hrtimer_rearm_deferred / print_cpu

write to 0xffff888237c1b8e8 of 8 bytes by task 12169 on cpu 0:
hrtimer_rearm kernel/time/hrtimer.c:2028 [inline]
__hrtimer_rearm_deferred+0x537/0x670 kernel/time/hrtimer.c:2059
hrtimer_rearm_deferred_tif include/linux/hrtimer_rearm.h:53 [inline]
hrtimer_rearm_deferred include/linux/hrtimer_rearm.h:62 [inline]
irqentry_exit_to_kernel_mode_after_preempt include/linux/irq-entry-common.h:513 [inline]
irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:550 [inline]
irqentry_exit+0x527/0x5b0 kernel/entry/common.c:164
sysvec_apic_timer_interrupt+0x44/0x80 arch/x86/kernel/apic/apic.c:1061
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
nf_hook_slow+0x58/0x180 net/netfilter/core.c:619
nf_hook include/linux/netfilter.h:273 [inline]
NF_HOOK include/linux/netfilter.h:316 [inline]
ip6_input+0x118/0x160 net/ipv6/ip6_input.c:540
dst_input include/net/dst.h:480 [inline]
ip6_sublist_rcv_finish net/ipv6/ip6_input.c:128 [inline]
ip6_list_rcv_finish net/ipv6/ip6_input.c:185 [inline]
ip6_sublist_rcv+0x8d6/0xa00 net/ipv6/ip6_input.c:361
ipv6_list_rcv+0x267/0x2a0 net/ipv6/ip6_input.c:395
__netif_receive_skb_list_ptype net/core/dev.c:6252 [inline]
__netif_receive_skb_list_core+0x3b0/0x500 net/core/dev.c:6299
__netif_receive_skb_list net/core/dev.c:6351 [inline]
netif_receive_skb_list_internal+0x47d/0x5f0 net/core/dev.c:6442
netif_receive_skb_list+0x33/0x1c0 net/core/dev.c:6494
xdp_recv_frames net/bpf/test_run.c:269 [inline]
xdp_test_run_batch net/bpf/test_run.c:350 [inline]
bpf_test_run_xdp_live+0x104c/0x1360 net/bpf/test_run.c:379
bpf_prog_test_run_xdp+0x57b/0xa10 net/bpf/test_run.c:1430
bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4742
__sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6266
__do_sys_bpf kernel/bpf/syscall.c:6361 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6359 [inline]
__x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6359
x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888237c1b8e8 of 8 bytes by task 12170 on cpu 1:
print_cpu+0x2fb/0x670 kernel/time/timer_list.c:129
timer_list_show+0x107/0x170 kernel/time/timer_list.c:291
seq_read_iter+0x636/0x940 fs/seq_file.c:273
proc_reg_read_iter+0x110/0x180 fs/proc/inode.c:299
copy_splice_read+0x471/0x6c0 fs/splice.c:362
do_splice_read fs/splice.c:980 [inline]
splice_direct_to_actor+0x26e/0x670 fs/splice.c:1084
do_splice_direct_actor fs/splice.c:1202 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1228
do_sendfile+0x382/0x650 fs/read_write.c:1372
__do_sys_sendfile64 fs/read_write.c:1433 [inline]
__se_sys_sendfile64 fs/read_write.c:1419 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x7fffffffffffffff -> 0x000000402d5241f2

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12170 Comm: syz.4.2929 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup