path: root/mm/page_vma_mapped.c
diff options
authorHugh Dickins <>2017-04-07 16:04:39 -0700
committerLinus Torvalds <>2017-04-08 00:47:48 -0700
commitd75450ff40df0199bf13dfb19f435519ff947138 (patch)
tree3eac1374291bf826d4af0c616e47f7ec4f7b4fe4 /mm/page_vma_mapped.c
parent81d4bab4ce87228c37ab14a885438544af5c9ce6 (diff)
mm: fix page_vma_mapped_walk() for ksm pages
Doug Smythies reports oops with KSM in this backtrace, I've been seeing the same: page_vma_mapped_walk+0xe6/0x5b0 page_referenced_one+0x91/0x1a0 rmap_walk_ksm+0x100/0x190 rmap_walk+0x4f/0x60 page_referenced+0x149/0x170 shrink_active_list+0x1c2/0x430 shrink_node_memcg+0x67a/0x7a0 shrink_node+0xe1/0x320 kswapd+0x34b/0x720 Just as observed in commit 4b0ece6fa016 ("mm: migrate: fix remove_migration_pte() for ksm pages"), you cannot use page->index calculations on ksm pages. page_vma_mapped_walk() is relying on __vma_address(), where a ksm page can lead it off the end of the page table, and into whatever nonsense is in the next page, ending as an oops inside check_pte()'s pte_page(). KSM tells page_vma_mapped_walk() exactly where to look for the page, it does not need any page->index calculation: and that's so also for all the normal and file and anon pages - just not for THPs and their subpages. Get out early in most cases: instead of a PageKsm test, move down the earlier not-THP-page test, as suggested by Kirill. I'm also slightly worried that this loop can stray into other vmas, so added a vm_end test to prevent surprises; though I have not imagined anything worse than a very contrived case, in which a page mlocked in the next vma might be reclaimed because it is not mlocked in this vma. Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()") Link: Signed-off-by: Hugh Dickins <> Reported-by: Doug Smythies <> Tested-by: Doug Smythies <> Reviewed-by: Kirill A. Shutemov <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/page_vma_mapped.c')
1 files changed, 8 insertions, 7 deletions
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index c4c9def8ffea..de9c40d7304a 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -111,12 +111,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
if (pvmw->pmd && !pvmw->pte)
return not_found(pvmw);
- /* Only for THP, seek to next pte entry makes sense */
- if (pvmw->pte) {
- if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
- return not_found(pvmw);
+ if (pvmw->pte)
goto next_pte;
- }
if (unlikely(PageHuge(pvmw->page))) {
/* when pud is not present, pte will be NULL */
@@ -165,9 +161,14 @@ restart:
while (1) {
if (check_pte(pvmw))
return true;
-next_pte: do {
+ /* Seek to next pte only makes sense for THP */
+ if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
+ return not_found(pvmw);
+ do {
pvmw->address += PAGE_SIZE;
- if (pvmw->address >=
+ if (pvmw->address >= pvmw->vma->vm_end ||
+ pvmw->address >=
__vma_address(pvmw->page, pvmw->vma) +
hpage_nr_pages(pvmw->page) * PAGE_SIZE)
return not_found(pvmw);