This is a note to let you know that I've just added the patch titled
thp: fix corner case of munlock() of PTE-mapped THPs
to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
thp-fix-corner-case-of-munlock-of-pte-mapped-thps.patch
and it can be found in the queue-4.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 655548bf6271b212cd1e4c259da9dbe616348d38 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Date: Wed, 30 Nov 2016 15:54:05 -0800
Subject: thp: fix corner case of munlock() of PTE-mapped THPs
From: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
commit 655548bf6271b212cd1e4c259da9dbe616348d38 upstream.
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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/mlock.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/mm/mlock.c
+++ b/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 stable-queue which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
queue-4.8/mm-thp-propagation-of-conditional-compilation-in-khugepaged.c.patch
queue-4.8/mm-fix-false-positive-warn_on-in-truncate-invalidate-for-hugetlb.patch
queue-4.8/thp-fix-corner-case-of-munlock-of-pte-mapped-thps.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html