kmem_cache_free(anon_vma_cachep, anon_vma);
}
-static inline struct anon_vma_chain *anon_vma_chain_alloc(void)
+static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
{
- return kmem_cache_alloc(anon_vma_chain_cachep, GFP_KERNEL);
+ return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
}
static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
struct mm_struct *mm = vma->vm_mm;
struct anon_vma *allocated;
- avc = anon_vma_chain_alloc();
+ avc = anon_vma_chain_alloc(GFP_KERNEL);
if (!avc)
goto out_enomem;
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)
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);
}
/*
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) {
- avc = anon_vma_chain_alloc();
- if (!avc)
- goto enomem_failure;
- anon_vma_chain_link(dst, avc, pavc->anon_vma);
+ struct anon_vma *anon_vma;
+
+ avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
+ if (unlikely(!avc)) {
+ unlock_anon_vma_root(root);
+ root = NULL;
+ avc = anon_vma_chain_alloc(GFP_KERNEL);
+ if (!avc)
+ goto enomem_failure;
+ }
+ 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:
anon_vma = anon_vma_alloc();
if (!anon_vma)
goto out_error;
- avc = anon_vma_chain_alloc();
+ avc = anon_vma_chain_alloc(GFP_KERNEL);
if (!avc)
goto out_error_free_anon_vma;
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;
return -ENOMEM;
}
-static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
-{
- struct anon_vma *anon_vma = anon_vma_chain->anon_vma;
- int empty;
-
- /* If anon_vma_fork fails, we can get an empty anon_vma_chain. */
- if (!anon_vma)
- return;
-
- anon_vma_lock(anon_vma);
- list_del(&anon_vma_chain->same_anon_vma);
-
- /* We must garbage collect the anon_vma if it's empty */
- empty = list_empty(&anon_vma->head);
- anon_vma_unlock(anon_vma);
-
- if (empty)
- put_anon_vma(anon_vma);
-}
-
void unlink_anon_vmas(struct vm_area_struct *vma)
{
struct anon_vma_chain *avc, *next;
+ struct anon_vma *root = NULL;
/*
* Unlink each anon_vma chained to the VMA. This list is ordered
* from newest to oldest, ensuring the root anon_vma gets freed last.
*/
list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
- anon_vma_unlink(avc);
+ struct anon_vma *anon_vma = avc->anon_vma;
+
+ root = lock_anon_vma_root(root, anon_vma);
+ list_del(&avc->same_anon_vma);
+
+ /*
+ * Leave empty anon_vmas on the list - we'll need
+ * to free them outside the lock.
+ */
+ if (list_empty(&anon_vma->head))
+ continue;
+
+ list_del(&avc->same_vma);
+ anon_vma_chain_free(avc);
+ }
+ unlock_anon_vma_root(root);
+
+ /*
+ * Iterate the list once more, it now only contains empty and unlinked
+ * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
+ * needing to acquire the anon_vma->root->mutex.
+ */
+ list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
+ struct anon_vma *anon_vma = avc->anon_vma;
+
+ put_anon_vma(anon_vma);
+
list_del(&avc->same_vma);
anon_vma_chain_free(avc);
}
* The page might have been remapped to a different anon_vma or the anon_vma
* returned may already be freed (and even reused).
*
+ * In case it was remapped to a different anon_vma, the new anon_vma will be a
+ * child of the old anon_vma, and the anon_vma lifetime rules will therefore
+ * ensure that any anon_vma obtained from the page will still be valid for as
+ * long as we observe page_mapped() [ hence all those page_mapped() tests ].
+ *
* All users of this function must be very careful when walking the anon_vma
* chain and verify that the page in question is indeed mapped in it
* [ something equivalent to page_mapped_in_vma() ].
/*
* If the page is still mapped, then this anon_vma is still
* its anon_vma, and holding the mutex ensures that it will
- * not go away, see __put_anon_vma().
+ * not go away, see anon_vma_free().
*/
if (!page_mapped(page)) {
mutex_unlock(&root_anon_vma->mutex);
projects / cascardo / linux.git / blobdiff