syzbot

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BUG: KCSAN: data-race in bq_flush_to_queue / cpu_map_kthread_run

write to 0xffff8881f5ece7c0 of 8 bytes by task 4675 on cpu 0:
 __ptr_ring_zero_tail include/linux/ptr_ring.h:259 [inline]
 __ptr_ring_discard_one include/linux/ptr_ring.h:291 [inline]
 __ptr_ring_consume include/linux/ptr_ring.h:311 [inline]
 __ptr_ring_consume_batched include/linux/ptr_ring.h:323 [inline]
 cpu_map_kthread_run+0x4fe/0x1680 kernel/bpf/cpumap.c:334
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff8881f5ece7c0 of 8 bytes by task 4672 on cpu 1:
 __ptr_ring_produce include/linux/ptr_ring.h:106 [inline]
 bq_flush_to_queue+0x124/0x360 kernel/bpf/cpumap.c:740
 __cpu_map_flush+0x47/0xa0 kernel/bpf/cpumap.c:825
 xdp_do_flush+0xf8/0x160 net/core/filter.c:4358
 xdp_test_run_batch net/bpf/test_run.c:348 [inline]
 bpf_test_run_xdp_live+0xe8a/0x1360 net/bpf/test_run.c:379
 bpf_prog_test_run_xdp+0x57b/0xa10 net/bpf/test_run.c:1397
 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4722
 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246
 __do_sys_bpf kernel/bpf/syscall.c:6341 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6339 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339
 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/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff8881182dd070 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4672 Comm: syz.3.9763 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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