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BUG: KCSAN: data-race in vm_area_dup / vma_interval_tree_remove

write to 0xffff8881230f69b8 of 8 bytes by task 7736 on cpu 0:
 __rb_erase_augmented include/linux/rbtree_augmented.h:218 [inline]
 rb_erase_augmented include/linux/rbtree_augmented.h:305 [inline]
 rb_erase_augmented_cached include/linux/rbtree_augmented.h:316 [inline]
 vma_interval_tree_remove+0x671/0x8a0 mm/interval_tree.c:23
 __remove_shared_vm_struct+0xad/0xd0 mm/mmap.c:154
 unlink_file_vma+0x69/0x90 mm/mmap.c:169
 free_pgtables+0x14f/0x200 mm/memory.c:396
 exit_mmap+0x151/0x300 mm/mmap.c:3162
 __mmput kernel/fork.c:1079 [inline]
 mmput+0xea/0x280 kernel/fork.c:1100
 exit_mm kernel/exit.c:485 [inline]
 do_exit+0x4c9/0x18f0 kernel/exit.c:804
 do_group_exit+0xb4/0x1c0 kernel/exit.c:921
 __do_sys_exit_group kernel/exit.c:932 [inline]
 __se_sys_exit_group kernel/exit.c:930 [inline]
 __x64_sys_exit_group+0x2e/0x30 kernel/exit.c:930
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881230f6960 of 200 bytes by task 7823 on cpu 1:
 vm_area_dup+0x70/0xf0 kernel/fork.c:359
 __split_vma+0x88/0x350 mm/mmap.c:2678
 __do_munmap+0xb02/0xb60 mm/mmap.c:2803
 do_munmap mm/mmap.c:2856 [inline]
 mmap_region+0x165/0xd50 mm/mmap.c:1749
 do_mmap+0x6d4/0xba0 mm/mmap.c:1577
 do_mmap_pgoff include/linux/mm.h:2348 [inline]
 vm_mmap_pgoff+0x12d/0x190 mm/util.c:496
 ksys_mmap_pgoff+0x2d8/0x420 mm/mmap.c:1629
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
 __x64_sys_mmap+0x2e/0x40 arch/x86/kernel/sys_x86_64.c:91
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7823 Comm: cat Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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