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BUG: KCSAN: data-race in mlock_fixup / try_to_unmap_one

write to 0xffff888100c31f50 of 8 bytes by task 4914 on cpu 0:
 mlock_fixup+0x220/0x310 mm/mlock.c:549
 apply_mlockall_flags+0x1ed/0x240 mm/mlock.c:767
 __do_sys_mlockall+0x19b/0x2d0 mm/mlock.c:795
 __se_sys_mlockall mm/mlock.c:774 [inline]
 __x64_sys_mlockall+0x1a/0x20 mm/mlock.c:774
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888100c31f50 of 8 bytes by task 4904 on cpu 1:
 try_to_unmap_one+0xb2/0x1320 mm/rmap.c:1409
 rmap_walk_file+0x1f9/0x300 mm/rmap.c:1936
 rmap_walk mm/rmap.c:1954 [inline]
 try_to_munlock+0x8f/0xd0 mm/rmap.c:1805
 __munlock_isolated_page mm/mlock.c:121 [inline]
 __munlock_pagevec+0x92d/0xb10 mm/mlock.c:321
 munlock_vma_pages_range+0x3d8/0x430 mm/mlock.c:474
 munlock_vma_pages_all mm/internal.h:362 [inline]
 exit_mmap+0x128/0x400 mm/mmap.c:3202
 __mmput+0x27/0x1c0 kernel/fork.c:1090
 mmput+0x3d/0x50 kernel/fork.c:1111
 exit_mm+0x360/0x450 kernel/exit.c:501
 do_exit+0x3ff/0x1560 kernel/exit.c:812
 do_group_exit+0x19b/0x1a0 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4904 Comm: syz-executor.2 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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