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BUG: KCSAN: data-race in copy_process / show_stat

read-write to 0xffffffff881e42d8 of 8 bytes by task 2 on cpu 0:
 copy_process+0x2928/0x2e70 kernel/fork.c:2296
 kernel_clone+0x14b/0x680 kernel/fork.c:2456
 kernel_thread+0x85/0xb0 kernel/fork.c:2508
 create_kthread kernel/kthread.c:315 [inline]
 kthreadd+0x2a7/0x350 kernel/kthread.c:633
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffffffff881e42d8 of 8 bytes by task 16262 on cpu 1:
 show_stat+0xc5e/0xdc0 fs/proc/stat.c:204
 seq_read+0x2de/0x890 fs/seq_file.c:208
 pde_read fs/proc/inode.c:306 [inline]
 proc_reg_read+0xe1/0x1b0 fs/proc/inode.c:316
 do_loop_readv_writev fs/read_write.c:742 [inline]
 do_iter_read+0x3b1/0x4b0 fs/read_write.c:784
 vfs_readv fs/read_write.c:902 [inline]
 do_preadv+0x139/0x210 fs/read_write.c:994
 __do_sys_preadv fs/read_write.c:1044 [inline]
 __se_sys_preadv fs/read_write.c:1039 [inline]
 __x64_sys_preadv+0x54/0x60 fs/read_write.c:1039
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16262 Comm: syz-executor.0 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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