The patch titled
Subject: thp: fix corner case of munlock() of PTE-mapped THPs
has been added to the -mm tree. Its filename is
mm-bug-in-munlock_vma_pages_range.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-bug-in-munlock_vma_pages_range.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-bug-in-munlock_vma_pages_range.patch
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: thp: fix corner case of munlock() of PTE-mapped THPs
The following program triggers BUG() in munlock_vma_pages_range():
// autogenerated by syzkaller (http://github.com/google/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: e90309c9f772 ("thp: allow mlocked THP again")
Link: http://lkml.kernel.org/r/20161115132703.7s7rrgmwttegcdh4@xxxxxxxxxxxxxxxxxx
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.5+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mlock.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff -puN mm/mlock.c~mm-bug-in-munlock_vma_pages_range mm/mlock.c
--- a/mm/mlock.c~mm-bug-in-munlock_vma_pages_range
+++ a/mm/mlock.c
@@ -190,10 +190,13 @@ unsigned int munlock_vma_page(struct pag
*/
spin_lock_irq(zone_lru_lock(zone));
- 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)) {
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mm-bug-in-munlock_vma_pages_range.patch
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