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BUG: KCSAN: data-race in exit_signals / get_task_mm

read-write to 0xffff888023ad6024 of 4 bytes by task 10225 on cpu 0:
 exit_signals+0x108/0x530 kernel/signal.c:2845
 do_exit+0x184/0x15e0 kernel/exit.c:762
 do_group_exit+0x16f/0x170 kernel/exit.c:903
 __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 0xffff888023ad6024 of 4 bytes by task 10227 on cpu 1:
 get_task_mm+0x3e/0x90 kernel/fork.c:1209
 proc_pid_status+0x35/0x1350 fs/proc/array.c:408
 proc_single_show+0x84/0x100 fs/proc/base.c:775
 seq_read+0x2de/0x890 fs/seq_file.c:208
 vfs_read+0x16d/0x5e0 fs/read_write.c:479
 ksys_read+0xce/0x180 fs/read_write.c:615
 __do_sys_read fs/read_write.c:625 [inline]
 __se_sys_read fs/read_write.c:623 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:623
 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: 10227 Comm: syz-executor.4 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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