syzbot

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BUG: KCSAN: data-race in do_group_exit / mm_release

write to 0xffff8880a670fa74 of 4 bytes by task 10867 on cpu 1:
 do_group_exit+0x137/0x180 kernel/exit.c:897
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:914
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:912
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:912
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a670fa74 of 4 bytes by task 10880 on cpu 0:
 mm_release+0x7f/0x190 kernel/fork.c:1297
 exit_mm_release+0x21/0x30 kernel/fork.c:1321
 exit_mm+0x4b/0x330 kernel/exit.c:438
 do_exit+0x40f/0x16c0 kernel/exit.c:793
 __do_sys_exit+0xb/0x10 kernel/exit.c:872
 __se_sys_exit+0x5/0x10 kernel/exit.c:870
 __x64_sys_exit+0x16/0x20 kernel/exit.c:870
 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: 0 PID: 10880 Comm: syz-executor.0 Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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