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BUG: KCSAN: data-race in copy_process / ksys_unshare

write to 0xffff88810083b300 of 4 bytes by task 15832 on cpu 1:
 copy_fs kernel/fork.c:1525 [inline]
 copy_process+0xf1d/0x2fa0 kernel/fork.c:2185
 kernel_clone+0x15c/0x680 kernel/fork.c:2584
 __do_sys_clone kernel/fork.c:2701 [inline]
 __se_sys_clone kernel/fork.c:2685 [inline]
 __x64_sys_clone+0xc6/0xf0 kernel/fork.c:2685
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810083b300 of 4 bytes by task 15841 on cpu 0:
 unshare_fs kernel/fork.c:2990 [inline]
 ksys_unshare+0x23d/0x740 kernel/fork.c:3068
 __do_sys_unshare kernel/fork.c:3151 [inline]
 __se_sys_unshare kernel/fork.c:3149 [inline]
 __x64_sys_unshare+0x1b/0x20 kernel/fork.c:3149
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000003 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15841 Comm: syz-executor.0 Not tainted 5.15.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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