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-rw-r--r--include/linux/rmap.h15
-rw-r--r--mm/ksm.c17
-rw-r--r--mm/migrate.c10
-rw-r--r--mm/rmap.c46
4 files changed, 69 insertions, 19 deletions
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index af43cb9a0506..dc9b3c0bf5d4 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -81,6 +81,13 @@ static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
{
return atomic_read(&anon_vma->external_refcount);
}
+
+static inline void get_anon_vma(struct anon_vma *anon_vma)
+{
+ atomic_inc(&anon_vma->external_refcount);
+}
+
+void drop_anon_vma(struct anon_vma *);
#else
static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma)
{
@@ -90,6 +97,14 @@ static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
{
return 0;
}
+
+static inline void get_anon_vma(struct anon_vma *anon_vma)
+{
+}
+
+static inline void drop_anon_vma(struct anon_vma *anon_vma)
+{
+}
#endif /* CONFIG_KSM */
static inline struct anon_vma *page_anon_vma(struct page *page)
diff --git a/mm/ksm.c b/mm/ksm.c
index da6037c261f1..9f2acc998a37 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -318,19 +318,14 @@ static void hold_anon_vma(struct rmap_item *rmap_item,
struct anon_vma *anon_vma)
{
rmap_item->anon_vma = anon_vma;
- atomic_inc(&anon_vma->external_refcount);
+ get_anon_vma(anon_vma);
}
-static void drop_anon_vma(struct rmap_item *rmap_item)
+static void ksm_drop_anon_vma(struct rmap_item *rmap_item)
{
struct anon_vma *anon_vma = rmap_item->anon_vma;
- if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
- int empty = list_empty(&anon_vma->head);
- anon_vma_unlock(anon_vma);
- if (empty)
- anon_vma_free(anon_vma);
- }
+ drop_anon_vma(anon_vma);
}
/*
@@ -415,7 +410,7 @@ static void break_cow(struct rmap_item *rmap_item)
* It is not an accident that whenever we want to break COW
* to undo, we also need to drop a reference to the anon_vma.
*/
- drop_anon_vma(rmap_item);
+ ksm_drop_anon_vma(rmap_item);
down_read(&mm->mmap_sem);
if (ksm_test_exit(mm))
@@ -470,7 +465,7 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node)
ksm_pages_sharing--;
else
ksm_pages_shared--;
- drop_anon_vma(rmap_item);
+ ksm_drop_anon_vma(rmap_item);
rmap_item->address &= PAGE_MASK;
cond_resched();
}
@@ -558,7 +553,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
else
ksm_pages_shared--;
- drop_anon_vma(rmap_item);
+ ksm_drop_anon_vma(rmap_item);
rmap_item->address &= PAGE_MASK;
} else if (rmap_item->address & UNSTABLE_FLAG) {
diff --git a/mm/migrate.c b/mm/migrate.c
index 5208fa1d9712..38e7cad782f4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -639,7 +639,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
* exist when the page is remapped later
*/
anon_vma = page_anon_vma(page);
- atomic_inc(&anon_vma->external_refcount);
+ get_anon_vma(anon_vma);
}
}
@@ -682,12 +682,8 @@ skip_unmap:
rcu_unlock:
/* Drop an anon_vma reference if we took one */
- if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
- int empty = list_empty(&anon_vma->head);
- anon_vma_unlock(anon_vma);
- if (empty)
- anon_vma_free(anon_vma);
- }
+ if (anon_vma)
+ drop_anon_vma(anon_vma);
if (rcu_locked)
rcu_read_unlock();
diff --git a/mm/rmap.c b/mm/rmap.c
index caa48b27371b..07e9814c7a41 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -235,6 +235,12 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
* lock any of the anon_vmas in this anon_vma tree.
*/
anon_vma->root = pvma->anon_vma->root;
+ /*
+ * With KSM refcounts, an anon_vma can stay around longer than the
+ * process it belongs to. The root anon_vma needs to be pinned
+ * until this anon_vma is freed, because the lock lives in the root.
+ */
+ get_anon_vma(anon_vma->root);
/* Mark this anon_vma as the one where our new (COWed) pages go. */
vma->anon_vma = anon_vma;
anon_vma_chain_link(vma, avc, anon_vma);
@@ -264,8 +270,12 @@ static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
empty = list_empty(&anon_vma->head) && !anonvma_external_refcount(anon_vma);
anon_vma_unlock(anon_vma);
- if (empty)
+ if (empty) {
+ /* We no longer need the root anon_vma */
+ if (anon_vma->root != anon_vma)
+ drop_anon_vma(anon_vma->root);
anon_vma_free(anon_vma);
+ }
}
void unlink_anon_vmas(struct vm_area_struct *vma)
@@ -1382,6 +1392,40 @@ int try_to_munlock(struct page *page)
return try_to_unmap_file(page, TTU_MUNLOCK);
}
+#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
+/*
+ * Drop an anon_vma refcount, freeing the anon_vma and anon_vma->root
+ * if necessary. Be careful to do all the tests under the lock. Once
+ * we know we are the last user, nobody else can get a reference and we
+ * can do the freeing without the lock.
+ */
+void drop_anon_vma(struct anon_vma *anon_vma)
+{
+ if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
+ struct anon_vma *root = anon_vma->root;
+ int empty = list_empty(&anon_vma->head);
+ int last_root_user = 0;
+ int root_empty = 0;
+
+ /*
+ * The refcount on a non-root anon_vma got dropped. Drop
+ * the refcount on the root and check if we need to free it.
+ */
+ if (empty && anon_vma != root) {
+ last_root_user = atomic_dec_and_test(&root->external_refcount);
+ root_empty = list_empty(&root->head);
+ }
+ anon_vma_unlock(anon_vma);
+
+ if (empty) {
+ anon_vma_free(anon_vma);
+ if (root_empty && last_root_user)
+ anon_vma_free(root);
+ }
+ }
+}
+#endif
+
#ifdef CONFIG_MIGRATION
/*
* rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():

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