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BUG: KCSAN: data-race in copy_mm / percpu_counter_destroy_many

write to 0xffff888103538bc8 of 8 bytes by task 23251 on cpu 1:
 __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+0x259/0x3f0 kernel/fork.c:734
 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+0x180/0x280 kernel/sched/core.c:5143
 context_switch kernel/sched/core.c:5263 [inline]
 __schedule+0x82d/0xc90 kernel/sched/core.c:6867
 __schedule_loop kernel/sched/core.c:6949 [inline]
 schedule+0x5e/0xd0 kernel/sched/core.c:6964
 io_schedule+0x3e/0x60 kernel/sched/core.c:7791
 folio_wait_bit_common+0x3ff/0x680 mm/filemap.c:1323
 folio_wait_bit+0x25/0x30 mm/filemap.c:1462
 folio_wait_writeback+0x57/0x140 mm/page-writeback.c:3089
 __filemap_fdatawait_range mm/filemap.c:532 [inline]
 file_write_and_wait_range+0x23b/0x2f0 mm/filemap.c:789
 generic_buffers_fsync_noflush+0x45/0x130 fs/buffer.c:609
 ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
 ext4_sync_file+0x1aa/0x680 fs/ext4/fsync.c:147
 vfs_fsync_range+0x10d/0x130 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2618 [inline]
 ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
 ext4_file_write_iter+0x380/0xf70 fs/ext4/file.c:-1
 iter_file_splice_write+0x6bc/0xa80 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x311/0x670 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1230
 do_sendfile+0x382/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881035386c0 of 1664 bytes by task 23287 on cpu 0:
 dup_mm kernel/fork.c:1523 [inline]
 copy_mm+0xe1/0x370 kernel/fork.c:1581
 copy_process+0xcbd/0x1f10 kernel/fork.c:2221
 kernel_clone+0x16b/0x5b0 kernel/fork.c:2651
 __do_sys_clone kernel/fork.c:2792 [inline]
 __se_sys_clone kernel/fork.c:2776 [inline]
 __x64_sys_clone+0x143/0x180 kernel/fork.c:2776
 x64_sys_call+0x12d0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:57
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 23287 Comm: dhcpcd-run-hook Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
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