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BUG: KCSAN: data-race in __bpf_get_stackid / bcmp

write to 0xffff88815d810658 of 120 bytes by task 9994 on cpu 1:
 __bpf_get_stackid+0x737/0x7d0 kernel/bpf/stackmap.c:311
 ____bpf_get_stackid kernel/bpf/stackmap.c:344 [inline]
 bpf_get_stackid+0xf3/0x130 kernel/bpf/stackmap.c:323
 ____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:1378 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run3+0x10f/0x1e0 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+0x327/0x3a0 mm/slub.c:6778
 anon_vma_chain_free mm/rmap.c:146 [inline]
 unlink_anon_vmas+0x325/0x360 mm/rmap.c:446
 free_pgtables+0x506/0x620 mm/memory.c:414
 exit_mmap+0x2f0/0x6b0 mm/mmap.c:1288
 __mmput+0x28/0x1c0 kernel/fork.c:1173
 mmput+0x40/0x50 kernel/fork.c:1196
 exit_mm+0xe4/0x180 kernel/exit.c:581
 do_exit+0x427/0x15d0 kernel/exit.c:959
 do_group_exit+0x139/0x140 kernel/exit.c:1112
 __do_sys_exit_group kernel/exit.c:1123 [inline]
 __se_sys_exit_group kernel/exit.c:1121 [inline]
 __x64_sys_exit_group+0x1f/0x20 kernel/exit.c:1121
 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+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88815d8106a8 of 8 bytes by task 3903 on cpu 0:
 memcmp lib/string.c:683 [inline]
 bcmp+0x23/0x90 lib/string.c:715
 memcmp include/linux/fortify-string.h:727 [inline]
 __bpf_get_stackid+0x382/0x7d0 kernel/bpf/stackmap.c:302
 ____bpf_get_stackid kernel/bpf/stackmap.c:344 [inline]
 bpf_get_stackid+0xf3/0x130 kernel/bpf/stackmap.c:323
 ____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:1378 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run3+0x10f/0x1e0 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+0x327/0x3a0 mm/slub.c:6778
 __merge_or_add_vmap_area mm/vmalloc.c:1474 [inline]
 merge_or_add_vmap_area_augment mm/vmalloc.c:1531 [inline]
 reclaim_list_global+0x22d/0xbd0 mm/vmalloc.c:2213
 decay_va_pool_node+0x862/0x890 mm/vmalloc.c:2268
 __purge_vmap_area_lazy+0xe4/0x770 mm/vmalloc.c:2348
 drain_vmap_area_work+0x25/0x40 mm/vmalloc.c:2423
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x582/0x770 kernel/workqueue.c:3421
 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: 0xffffffff812f0f99 -> 0xffffffff813929f9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3903 Comm: kworker/0:7 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events drain_vmap_area_work
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