Commit 655548bf authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds

thp: fix corner case of munlock() of PTE-mapped THPs

The following program triggers BUG() in munlock_vma_pages_range():

	// autogenerated by syzkaller (
	#include <sys/mman.h>

	int main()
	  mmap((void*)0x20105000ul, 0xc00000ul, 0x2ul, 0x2172ul, -1, 0);
	  mremap((void*)0x201fd000ul, 0x4000ul, 0xc00000ul, 0x3ul, 0x203f0000ul);
	  return 0;

The test-case constructs the situation when munlock_vma_pages_range()
finds PTE-mapped THP-head in the middle of page table and, by mistake,
skips HPAGE_PMD_NR pages after that.

As result, on the next iteration it hits the middle of PMD-mapped THP
and gets upset seeing mlocked tail page.

The solution is only skip HPAGE_PMD_NR pages if the THP was mlocked
during munlock_vma_page().  It would guarantee that the page is
PMD-mapped as we never mlock PTE-mapeed THPs.

Fixes: e90309c9 ("thp: allow mlocked THP again")
Link: 's avatarKirill A. Shutemov <>
Reported-by: 's avatarDmitry Vyukov <>
Cc: Konstantin Khlebnikov <>
Cc: Andrey Ryabinin <>
Cc: syzkaller <>
Cc: Andrea Arcangeli <>
Cc: <>	[4.5+]
Signed-off-by: 's avatarAndrew Morton <>
Signed-off-by: 's avatarLinus Torvalds <>
parent e1465d12
......@@ -190,10 +190,13 @@ unsigned int munlock_vma_page(struct page *page)
nr_pages = hpage_nr_pages(page);
if (!TestClearPageMlocked(page))
if (!TestClearPageMlocked(page)) {
/* Potentially, PTE-mapped THP: do not skip the rest PTEs */
nr_pages = 1;
goto unlock_out;
nr_pages = hpage_nr_pages(page);
__mod_zone_page_state(zone, NR_MLOCK, -nr_pages);
if (__munlock_isolate_lru_page(page, true)) {
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