==================================================================
BUG: KCSAN: data-race in copy_mm / percpu_counter_destroy_many

write to 0xffff88811a013458 of 8 bytes by task 7637 on cpu 0:
 __list_del include/linux/list.h:203 [inline]
 __list_del_entry include/linux/list.h:226 [inline]
 list_del include/linux/list.h:237 [inline]
 percpu_counter_destroy_many+0xc7/0x2b0 lib/percpu_counter.c:244
 __mmdrop+0x25d/0x3f0 kernel/fork.c:737
 mmdrop include/linux/sched/mm.h:55 [inline]
 mmdrop_sched include/linux/sched/mm.h:83 [inline]
 mmdrop_lazy_tlb_sched include/linux/sched/mm.h:110 [inline]
 finish_task_switch+0x225/0x320 kernel/sched/core.c:5270
 context_switch kernel/sched/core.c:5391 [inline]
 __schedule+0x951/0xd40 kernel/sched/core.c:7189
 preempt_schedule_common+0x11/0x30 kernel/sched/core.c:7370
 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12
 alloc_from_pcs mm/slub.c:4771 [inline]
 slab_alloc_node mm/slub.c:4883 [inline]
 __kmalloc_cache_noprof+0x24c/0x400 mm/slub.c:5414
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 inetdev_init+0x4f/0x340 net/ipv4/devinet.c:273
 inetdev_event+0x404/0xba0 net/ipv4/devinet.c:1590
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x72/0x1a0 kernel/notifier.c:453
 call_netdevice_notifiers_info net/core/dev.c:2249 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2287 [inline]
 call_netdevice_notifiers+0xb5/0x110 net/core/dev.c:2301
 register_netdevice+0xf7b/0x1160 net/core/dev.c:11461
 __ip_tunnel_create+0x31d/0x430 net/ipv4/ip_tunnel.c:268
 ip_tunnel_init_net+0x210/0x490 net/ipv4/ip_tunnel.c:1147
 ipgre_tap_init_net+0x35/0x40 net/ipv4/ip_gre.c:1762
 ops_init+0x22a/0x2e0 net/core/net_namespace.c:137
 setup_net+0x9f/0x230 net/core/net_namespace.c:446
 copy_net_ns+0x310/0x450 net/core/net_namespace.c:579
 create_new_namespaces+0x20e/0x440 kernel/nsproxy.c:132
 unshare_nsproxy_namespaces+0x115/0x150 kernel/nsproxy.c:234
 ksys_unshare+0x402/0x740 kernel/fork.c:3243
 __do_sys_unshare kernel/fork.c:3317 [inline]
 __se_sys_unshare kernel/fork.c:3315 [inline]
 __x64_sys_unshare+0x1f/0x30 kernel/fork.c:3315
 x64_sys_call+0x1cef/0x3020 arch/x86/include/generated/asm/syscalls_64.h:273
 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 0xffff88811a012f40 of 1664 bytes by task 7670 on cpu 1:
 dup_mm kernel/fork.c:1528 [inline]
 copy_mm+0xe1/0x370 kernel/fork.c:1586
 copy_process+0x1087/0x2370 kernel/fork.c:2264
 kernel_clone+0x1a5/0x5e0 kernel/fork.c:2721
 __do_sys_clone kernel/fork.c:2862 [inline]
 __se_sys_clone kernel/fork.c:2846 [inline]
 __x64_sys_clone+0x143/0x180 kernel/fork.c:2846
 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+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 7670 Comm: dhcpcd-run-hook Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================