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-rw-r--r--mm/rmap.c39
1 files changed, 36 insertions, 3 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index 0eb463ea88dd..f286697c61dc 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -200,6 +200,32 @@ int anon_vma_prepare(struct vm_area_struct *vma)
return -ENOMEM;
}
+/*
+ * This is a useful helper function for locking the anon_vma root as
+ * we traverse the vma->anon_vma_chain, looping over anon_vma's that
+ * have the same vma.
+ *
+ * Such anon_vma's should have the same root, so you'd expect to see
+ * just a single mutex_lock for the whole traversal.
+ */
+static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
+{
+ struct anon_vma *new_root = anon_vma->root;
+ if (new_root != root) {
+ if (WARN_ON_ONCE(root))
+ mutex_unlock(&root->mutex);
+ root = new_root;
+ mutex_lock(&root->mutex);
+ }
+ return root;
+}
+
+static inline void unlock_anon_vma_root(struct anon_vma *root)
+{
+ if (root)
+ mutex_unlock(&root->mutex);
+}
+
static void anon_vma_chain_link(struct vm_area_struct *vma,
struct anon_vma_chain *avc,
struct anon_vma *anon_vma)
@@ -208,13 +234,11 @@ static void anon_vma_chain_link(struct vm_area_struct *vma,
avc->anon_vma = anon_vma;
list_add(&avc->same_vma, &vma->anon_vma_chain);
- anon_vma_lock(anon_vma);
/*
* It's critical to add new vmas to the tail of the anon_vma,
* see comment in huge_memory.c:__split_huge_page().
*/
list_add_tail(&avc->same_anon_vma, &anon_vma->head);
- anon_vma_unlock(anon_vma);
}
/*
@@ -224,16 +248,23 @@ static void anon_vma_chain_link(struct vm_area_struct *vma,
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
struct anon_vma_chain *avc, *pavc;
+ struct anon_vma *root = NULL;
list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
+ struct anon_vma *anon_vma;
+
avc = anon_vma_chain_alloc();
if (!avc)
goto enomem_failure;
- anon_vma_chain_link(dst, avc, pavc->anon_vma);
+ anon_vma = pavc->anon_vma;
+ root = lock_anon_vma_root(root, anon_vma);
+ anon_vma_chain_link(dst, avc, anon_vma);
}
+ unlock_anon_vma_root(root);
return 0;
enomem_failure:
+ unlock_anon_vma_root(root);
unlink_anon_vmas(dst);
return -ENOMEM;
}
@@ -280,7 +311,9 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
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_lock(anon_vma);
anon_vma_chain_link(vma, avc, anon_vma);
+ anon_vma_unlock(anon_vma);
return 0;