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-rw-r--r--mm/mlock.c29
1 files changed, 22 insertions, 7 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index d480cd6..c59c420 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -133,7 +133,10 @@ static void __munlock_isolation_failed(struct page *page)
/**
* munlock_vma_page - munlock a vma page
- * @page - page to be unlocked
+ * @page - page to be unlocked, either a normal page or THP page head
+ *
+ * returns the size of the page as a page mask (0 for normal page,
+ * HPAGE_PMD_NR - 1 for THP head page)
*
* called from munlock()/munmap() path with page supposedly on the LRU.
* When we munlock a page, because the vma where we found the page is being
@@ -148,21 +151,30 @@ static void __munlock_isolation_failed(struct page *page)
*/
unsigned int munlock_vma_page(struct page *page)
{
- unsigned int page_mask = 0;
+ unsigned int nr_pages;
BUG_ON(!PageLocked(page));
if (TestClearPageMlocked(page)) {
- unsigned int nr_pages = hpage_nr_pages(page);
+ nr_pages = hpage_nr_pages(page);
mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
- page_mask = nr_pages - 1;
if (!isolate_lru_page(page))
__munlock_isolated_page(page);
else
__munlock_isolation_failed(page);
+ } else {
+ nr_pages = hpage_nr_pages(page);
}
- return page_mask;
+ /*
+ * Regardless of the original PageMlocked flag, we determine nr_pages
+ * after touching the flag. This leaves a possible race with a THP page
+ * split, such that a whole THP page was munlocked, but nr_pages == 1.
+ * Returning a smaller mask due to that is OK, the worst that can
+ * happen is subsequent useless scanning of the former tail pages.
+ * The NR_MLOCK accounting can however become broken.
+ */
+ return nr_pages - 1;
}
/**
@@ -440,7 +452,8 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
while (start < end) {
struct page *page = NULL;
- unsigned int page_mask, page_increm;
+ unsigned int page_mask;
+ unsigned long page_increm;
struct pagevec pvec;
struct zone *zone;
int zoneid;
@@ -490,7 +503,9 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
goto next;
}
}
- page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
+ /* It's a bug to munlock in the middle of a THP page */
+ VM_BUG_ON((start >> PAGE_SHIFT) & page_mask);
+ page_increm = 1 + page_mask;
start += page_increm * PAGE_SIZE;
next:
cond_resched();
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