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BUG: KCSAN: data-race in __bpf_get_stackid / bcmp

write to 0xffff88811aaa29f0 of 120 bytes by task 16530 on cpu 0:
 __bpf_get_stackid+0x761/0x800 kernel/bpf/stackmap.c:288
 ____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
 bpf_get_stackid+0xef/0x120 kernel/bpf/stackmap.c:300
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1628 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1617
 bpf_prog_53f0063d4d7f65ce+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1350 [inline]
 __bpf_prog_run include/linux/filter.h:721 [inline]
 bpf_prog_run include/linux/filter.h:728 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run3+0x10f/0x1d0 kernel/trace/bpf_trace.c:2117
 __do_trace_kmem_cache_free include/trace/events/kmem.h:117 [inline]
 trace_kmem_cache_free include/trace/events/kmem.h:117 [inline]
 kmem_cache_free+0x329/0x3d0 mm/slub.c:6751
 anon_vma_chain_free mm/rmap.c:146 [inline]
 unlink_anon_vmas+0x325/0x360 mm/rmap.c:446
 free_pgtables+0x4fc/0x610 mm/memory.c:414
 exit_mmap+0x2f6/0x6c0 mm/mmap.c:1291
 __mmput+0x28/0x1c0 kernel/fork.c:1131
 mmput+0x40/0x50 kernel/fork.c:1154
 exit_mm+0xe4/0x180 kernel/exit.c:583
 do_exit+0x427/0x15d0 kernel/exit.c:961
 do_group_exit+0x139/0x140 kernel/exit.c:1114
 __do_sys_exit_group kernel/exit.c:1125 [inline]
 __se_sys_exit_group kernel/exit.c:1123 [inline]
 __x64_sys_exit_group+0x1f/0x20 kernel/exit.c:1123
 x64_sys_call+0x2fff/0x3000 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811aaa2a10 of 8 bytes by interrupt on cpu 1:
 memcmp lib/string.c:683 [inline]
 bcmp+0x23/0x90 lib/string.c:715
 memcmp include/linux/fortify-string.h:727 [inline]
 __bpf_get_stackid+0x371/0x800 kernel/bpf/stackmap.c:279
 ____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
 bpf_get_stackid+0xef/0x120 kernel/bpf/stackmap.c:300
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1628 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1617
 bpf_prog_53f0063d4d7f65ce+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1350 [inline]
 __bpf_prog_run include/linux/filter.h:721 [inline]
 bpf_prog_run include/linux/filter.h:728 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run3+0x10f/0x1d0 kernel/trace/bpf_trace.c:2117
 __do_trace_kmem_cache_free include/trace/events/kmem.h:117 [inline]
 trace_kmem_cache_free include/trace/events/kmem.h:117 [inline]
 kmem_cache_free+0x329/0x3d0 mm/slub.c:6751
 root_free_rcu+0x120/0x170 drivers/net/wireguard/allowedips.c:65
 rcu_do_batch kernel/rcu/tree.c:2605 [inline]
 rcu_core+0x5d7/0xc60 kernel/rcu/tree.c:2857
 rcu_core_si+0xd/0x20 kernel/rcu/tree.c:2874
 handle_softirqs+0xba/0x290 kernel/softirq.c:622
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1063
 smpboot_thread_fn+0x32b/0x530 kernel/smpboot.c:160
 kthread+0x489/0x510 kernel/kthread.c:463
 ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0xffffffff81499757 -> 0xffffffff8182fc9c

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 22 Comm: ksoftirqd/1 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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