[PATCH] mm: migration page refcounting fix
Migration code currently does not take a reference to target page
properly, so between unlocking the pte and trying to take a new
reference to the page with isolate_lru_page, anything could happen to
it.
Fix this by holding the pte lock until we get a chance to elevate the
refcount.
Other small cleanups while we're here.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3171f88..551cde4 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -208,6 +208,17 @@
page = vm_normal_page(vma, addr, *pte);
if (!page)
continue;
+ /*
+ * The check for PageReserved here is important to avoid
+ * handling zero pages and other pages that may have been
+ * marked special by the system.
+ *
+ * If the PageReserved would not be checked here then f.e.
+ * the location of the zero page could have an influence
+ * on MPOL_MF_STRICT, zero pages would be counted for
+ * the per node stats, and there would be useless attempts
+ * to put zero pages on the migration list.
+ */
if (PageReserved(page))
continue;
nid = page_to_nid(page);
@@ -216,11 +227,8 @@
if (flags & MPOL_MF_STATS)
gather_stats(page, private);
- else if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
- spin_unlock(ptl);
+ else if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
migrate_page_add(vma, page, private, flags);
- spin_lock(ptl);
- }
else
break;
} while (pte++, addr += PAGE_SIZE, addr != end);
@@ -309,6 +317,10 @@
int err;
struct vm_area_struct *first, *vma, *prev;
+ /* Clear the LRU lists so pages can be isolated */
+ if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
+ lru_add_drain_all();
+
first = find_vma(mm, start);
if (!first)
return ERR_PTR(-EFAULT);
@@ -555,15 +567,8 @@
if ((flags & MPOL_MF_MOVE_ALL) || !page->mapping || PageAnon(page) ||
mapping_writably_mapped(page->mapping) ||
single_mm_mapping(vma->vm_mm, page->mapping)) {
- int rc = isolate_lru_page(page);
-
- if (rc == 1)
+ if (isolate_lru_page(page))
list_add(&page->lru, pagelist);
- /*
- * If the isolate attempt was not successful then we just
- * encountered an unswappable page. Something must be wrong.
- */
- WARN_ON(rc == 0);
}
}