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-rw-r--r--mm/ksm.c23
1 files changed, 13 insertions, 10 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index 70daa35266ef..e02430fb26f6 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -514,15 +514,14 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node)
* but this is different - made simpler by ksm_thread_mutex being held, but
* interesting for assuming that no other use of the struct page could ever
* put our expected_mapping into page->mapping (or a field of the union which
- * coincides with page->mapping). The RCU calls are not for KSM at all, but
- * to keep the page_count protocol described with page_cache_get_speculative.
+ * coincides with page->mapping).
*
* Note: it is possible that get_ksm_page() will return NULL one moment,
* then page the next, if the page is in between page_freeze_refs() and
* page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
* is on its way to being freed; but it is an anomaly to bear in mind.
*/
-static struct page *get_ksm_page(struct stable_node *stable_node)
+static struct page *get_ksm_page(struct stable_node *stable_node, bool locked)
{
struct page *page;
void *expected_mapping;
@@ -530,7 +529,6 @@ static struct page *get_ksm_page(struct stable_node *stable_node)
page = pfn_to_page(stable_node->kpfn);
expected_mapping = (void *)stable_node +
(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
- rcu_read_lock();
if (page->mapping != expected_mapping)
goto stale;
if (!get_page_unless_zero(page))
@@ -539,10 +537,16 @@ static struct page *get_ksm_page(struct stable_node *stable_node)
put_page(page);
goto stale;
}
- rcu_read_unlock();
+ if (locked) {
+ lock_page(page);
+ if (page->mapping != expected_mapping) {
+ unlock_page(page);
+ put_page(page);
+ goto stale;
+ }
+ }
return page;
stale:
- rcu_read_unlock();
remove_node_from_stable_tree(stable_node);
return NULL;
}
@@ -558,11 +562,10 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
struct page *page;
stable_node = rmap_item->head;
- page = get_ksm_page(stable_node);
+ page = get_ksm_page(stable_node, true);
if (!page)
goto out;
- lock_page(page);
hlist_del(&rmap_item->hlist);
unlock_page(page);
put_page(page);
@@ -1042,7 +1045,7 @@ static struct page *stable_tree_search(struct page *page)
cond_resched();
stable_node = rb_entry(node, struct stable_node, node);
- tree_page = get_ksm_page(stable_node);
+ tree_page = get_ksm_page(stable_node, false);
if (!tree_page)
return NULL;
@@ -1086,7 +1089,7 @@ static struct stable_node *stable_tree_insert(struct page *kpage)
cond_resched();
stable_node = rb_entry(*new, struct stable_node, node);
- tree_page = get_ksm_page(stable_node);
+ tree_page = get_ksm_page(stable_node, false);
if (!tree_page)
return NULL;