KCSAN: data-race in __rb_rotate_set_parents / vm_area_dup

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    05f22368 x86, kcsan: Enable KCSAN for x86
git tree:       https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=1060c47b600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
dashboard link: https://syzkaller.appspot.com/bug?extid=c034966b0b02f94f7f34
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c034966b0b02f94f7f34@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KCSAN: data-race in __rb_rotate_set_parents / vm_area_dup

read to 0xffff88811eef53e8 of 200 bytes by task 7738 on cpu 0:
 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:2353 [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+0x91/0xc0 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

write to 0xffff88811eef5440 of 8 bytes by task 7737 on cpu 1:
 __rb_rotate_set_parents+0x4d/0xf0 lib/rbtree.c:79
 __rb_insert lib/rbtree.c:215 [inline]
 __rb_insert_augmented+0x109/0x370 lib/rbtree.c:459
 rb_insert_augmented include/linux/rbtree_augmented.h:50 [inline]
 rb_insert_augmented_cached include/linux/rbtree_augmented.h:60 [inline]
 vma_interval_tree_insert+0x196/0x230 mm/interval_tree.c:23
 __vma_link_file+0xd9/0x110 mm/mmap.c:634
 __vma_adjust+0x1ac/0x12a0 mm/mmap.c:842
 vma_adjust include/linux/mm.h:2276 [inline]
 __split_vma+0x208/0x350 mm/mmap.c:2707
 split_vma+0x73/0xa0 mm/mmap.c:2736
 mprotect_fixup+0x43f/0x510 mm/mprotect.c:413
 do_mprotect_pkey+0x3eb/0x660 mm/mprotect.c:553
 __do_sys_mprotect mm/mprotect.c:578 [inline]
 __se_sys_mprotect mm/mprotect.c:575 [inline]
 __x64_sys_mprotect+0x51/0x70 mm/mprotect.c:575
 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: 7737 Comm: blkid Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
==================================================================


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