[syzbot] [netfilter?] BUG: using smp_processor_id() in preemptible code in cpu_mt

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 50d00ea66086 Merge branch 'bpf-follow-up-fixes-for-stack-a..
git tree: bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17f258c8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4caf64b1ee83dac0
dashboard link: https://syzkaller.appspot.com/bug?extid=690d3e3ffa7335ac10eb
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/dbc6ccaf15bc/disk-50d00ea6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9160c9066e5c/vmlinux-50d00ea6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b6f1c3abffde/bzImage-50d00ea6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+690d3e...@syzkaller.appspotmail.com

BUG: using smp_processor_id() in preemptible [00000000] code: syz.3.1377/11941
caller is cpu_mt+0x53/0xd0 net/netfilter/xt_cpu.c:37
CPU: 1 UID: 0 PID: 11941 Comm: syz.3.1377 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
check_preemption_disabled+0xd3/0xe0 lib/smp_processor_id.c:47
cpu_mt+0x53/0xd0 net/netfilter/xt_cpu.c:37
__nft_match_eval net/netfilter/nft_compat.c:412 [inline]
nft_match_eval+0x1ad/0x2b0 net/netfilter/nft_compat.c:442
expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline]
nft_do_chain+0x48d/0x1ae0 net/netfilter/nf_tables_core.c:285
nft_do_chain_inet+0x360/0x4b0 net/netfilter/nft_chain_filter.c:162
nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
nf_hook_slow+0xc5/0x220 net/netfilter/core.c:619
nf_hook+0x22a/0x3a0 include/linux/netfilter.h:273
NF_HOOK_COND include/linux/netfilter.h:306 [inline]
ip_output+0x269/0x450 net/ipv4/ip_output.c:438
__ip_queue_xmit+0x116a/0x1bb0 net/ipv4/ip_output.c:534
sctp_packet_transmit+0x246f/0x2ac0 net/sctp/output.c:653
sctp_packet_singleton+0x234/0x340 net/sctp/outqueue.c:783
sctp_outq_flush_ctrl net/sctp/outqueue.c:914 [inline]
sctp_outq_flush+0x50d/0x31b0 net/sctp/outqueue.c:1212
sctp_cmd_interpreter net/sctp/sm_sideeffect.c:-1 [inline]
sctp_side_effects net/sctp/sm_sideeffect.c:1204 [inline]
sctp_do_sm+0x54c7/0x5cf0 net/sctp/sm_sideeffect.c:1175
sctp_primitive_ASSOCIATE+0x95/0xc0 net/sctp/primitive.c:73
sctp_sendmsg_to_asoc+0x143d/0x1900 net/sctp/socket.c:1840
sctp_sendmsg+0x1b3d/0x2c10 net/sctp/socket.c:2030
sock_sendmsg_nosec net/socket.c:787 [inline]
__sock_sendmsg net/socket.c:802 [inline]
____sys_sendmsg+0x80a/0x9f0 net/socket.c:2698
___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
__sys_sendmsg net/socket.c:2784 [inline]
__do_sys_sendmsg net/socket.c:2789 [inline]
__se_sys_sendmsg net/socket.c:2787 [inline]
__x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff6e519ce59
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:00007ff6e33f6028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ff6e5415fa0 RCX: 00007ff6e519ce59
RDX: 00000000000480d1 RSI: 0000200000000140 RDI: 0000000000000003
RBP: 00007ff6e5232d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff6e5416038 R14: 00007ff6e5415fa0 R15: 00007ffdfe9dd548
</TASK>


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