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BUG: KCSAN: data-race in munlock_vma_pages_range / try_to_unmap_one

read-write to 0xffff888137a438e8 of 8 bytes by task 15958 on cpu 0:
 munlock_vma_pages_range+0x44/0x760 mm/mlock.c:453
 munlock_vma_pages_all mm/internal.h:342 [inline]
 exit_mmap+0x128/0x3b0 mm/mmap.c:3206
 __mmput+0xa2/0x220 kernel/fork.c:1079
 mmput+0x38/0x40 kernel/fork.c:1100
 exit_mm+0x2bd/0x320 kernel/exit.c:483
 do_exit+0x3c2/0x15a0 kernel/exit.c:793
 do_group_exit+0xa0/0x170 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 0xffff888137a438e8 of 8 bytes by task 15932 on cpu 1:
 try_to_unmap_one+0x544/0x1720 mm/rmap.c:1442
 rmap_walk_file+0x260/0x4f0 mm/rmap.c:1933
 rmap_walk mm/rmap.c:1951 [inline]
 try_to_munlock+0xe7/0x150 mm/rmap.c:1802
 __munlock_isolated_page mm/mlock.c:141 [inline]
 __munlock_pagevec+0x57d/0x830 mm/mlock.c:351
 munlock_vma_pages_range+0x581/0x760 mm/mlock.c:504
 munlock_vma_pages_all mm/internal.h:342 [inline]
 exit_mmap+0x128/0x3b0 mm/mmap.c:3206
 __mmput+0xa2/0x220 kernel/fork.c:1079
 mmput+0x38/0x40 kernel/fork.c:1100
 exit_mm+0x2bd/0x320 kernel/exit.c:483
 do_exit+0x3c2/0x15a0 kernel/exit.c:793
 do_group_exit+0xa0/0x170 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15932 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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