1 files changed, 130 insertions, 26 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 5cb4711..be34094 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -62,6 +62,7 @@
 #include "internal.h"
 
 static struct kmem_cache *anon_vma_cachep;
+static struct kmem_cache *anon_vma_chain_cachep;
 
 static inline struct anon_vma *anon_vma_alloc(void)
 {
@@ -73,6 +74,16 @@ void anon_vma_free(struct anon_vma *anon_vma)
 	kmem_cache_free(anon_vma_cachep, anon_vma);
 }
 
+static inline struct anon_vma_chain *anon_vma_chain_alloc(void)
+{
+	return kmem_cache_alloc(anon_vma_chain_cachep, GFP_KERNEL);
+}
+
+void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
+{
+	kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
+}
+
 /**
  * anon_vma_prepare - attach an anon_vma to a memory region
  * @vma: the memory region in question
@@ -103,18 +114,23 @@ void anon_vma_free(struct anon_vma *anon_vma)
 int anon_vma_prepare(struct vm_area_struct *vma)
 {
 	struct anon_vma *anon_vma = vma->anon_vma;
+	struct anon_vma_chain *avc;
 
 	might_sleep();
 	if (unlikely(!anon_vma)) {
 		struct mm_struct *mm = vma->vm_mm;
 		struct anon_vma *allocated;
 
+		avc = anon_vma_chain_alloc();
+		if (!avc)
+			goto out_enomem;
+
 		anon_vma = find_mergeable_anon_vma(vma);
 		allocated = NULL;
 		if (!anon_vma) {
 			anon_vma = anon_vma_alloc();
 			if (unlikely(!anon_vma))
-				return -ENOMEM;
+				goto out_enomem_free_avc;
 			allocated = anon_vma;
 		}
 		spin_lock(&anon_vma->lock);
@@ -123,53 +139,113 @@ int anon_vma_prepare(struct vm_area_struct *vma)
 		spin_lock(&mm->page_table_lock);
 		if (likely(!vma->anon_vma)) {
 			vma->anon_vma = anon_vma;
-			list_add_tail(&vma->anon_vma_node, &anon_vma->head);
+			avc->anon_vma = anon_vma;
+			avc->vma = vma;
+			list_add(&avc->same_vma, &vma->anon_vma_chain);
+			list_add(&avc->same_anon_vma, &anon_vma->head);
 			allocated = NULL;
 		}
 		spin_unlock(&mm->page_table_lock);
 
 		spin_unlock(&anon_vma->lock);
-		if (unlikely(allocated))
+		if (unlikely(allocated)) {
 			anon_vma_free(allocated);
+			anon_vma_chain_free(avc);
+		}
 	}
 	return 0;
+
+ out_enomem_free_avc:
+	anon_vma_chain_free(avc);
+ out_enomem:
+	return -ENOMEM;
 }
 
-void __anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next)
+static void anon_vma_chain_link(struct vm_area_struct *vma,
+				struct anon_vma_chain *avc,
+				struct anon_vma *anon_vma)
 {
-	BUG_ON(vma->anon_vma != next->anon_vma);
-	list_del(&next->anon_vma_node);
+	avc->vma = vma;
+	avc->anon_vma = anon_vma;
+	list_add(&avc->same_vma, &vma->anon_vma_chain);
+
+	spin_lock(&anon_vma->lock);
+	list_add_tail(&avc->same_anon_vma, &anon_vma->head);
+	spin_unlock(&anon_vma->lock);
 }
 
-void __anon_vma_link(struct vm_area_struct *vma)
+/*
+ * Attach the anon_vmas from src to dst.
+ * Returns 0 on success, -ENOMEM on failure.
+ */
+int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 {
-	struct anon_vma *anon_vma = vma->anon_vma;
+	struct anon_vma_chain *avc, *pavc;
+
+	list_for_each_entry(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);
+	}
+	return 0;
 
-	if (anon_vma)
-		list_add_tail(&vma->anon_vma_node, &anon_vma->head);
+ enomem_failure:
+	unlink_anon_vmas(dst);
+	return -ENOMEM;
 }
 
-void anon_vma_link(struct vm_area_struct *vma)
+/*
+ * Attach vma to its own anon_vma, as well as to the anon_vmas that
+ * the corresponding VMA in the parent process is attached to.
+ * Returns 0 on success, non-zero on failure.
+ */
+int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
 {
-	struct anon_vma *anon_vma = vma->anon_vma;
+	struct anon_vma_chain *avc;
+	struct anon_vma *anon_vma;
 
-	if (anon_vma) {
-		spin_lock(&anon_vma->lock);
-		list_add_tail(&vma->anon_vma_node, &anon_vma->head);
-		spin_unlock(&anon_vma->lock);
-	}
+	/* Don't bother if the parent process has no anon_vma here. */
+	if (!pvma->anon_vma)
+		return 0;
+
+	/*
+	 * First, attach the new VMA to the parent VMA's anon_vmas,
+	 * so rmap can find non-COWed pages in child processes.
+	 */
+	if (anon_vma_clone(vma, pvma))
+		return -ENOMEM;
+
+	/* Then add our own anon_vma. */
+	anon_vma = anon_vma_alloc();
+	if (!anon_vma)
+		goto out_error;
+	avc = anon_vma_chain_alloc();
+	if (!avc)
+		goto out_error_free_anon_vma;
+	anon_vma_chain_link(vma, avc, anon_vma);
+	/* Mark this anon_vma as the one where our new (COWed) pages go. */
+	vma->anon_vma = anon_vma;
+
+	return 0;
+
+ out_error_free_anon_vma:
+	anon_vma_free(anon_vma);
+ out_error:
+	return -ENOMEM;
 }
 
-void anon_vma_unlink(struct vm_area_struct *vma)
+static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
 {
-	struct anon_vma *anon_vma = vma->anon_vma;
+	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;
 
 	spin_lock(&anon_vma->lock);
-	list_del(&vma->anon_vma_node);
+	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) && !ksm_refcount(anon_vma);
@@ -179,6 +255,18 @@ void anon_vma_unlink(struct vm_area_struct *vma)
 		anon_vma_free(anon_vma);
 }
 
+void unlink_anon_vmas(struct vm_area_struct *vma)
+{
+	struct anon_vma_chain *avc, *next;
+
+	/* Unlink each anon_vma chained to the VMA. */
+	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
+		anon_vma_unlink(avc);
+		list_del(&avc->same_vma);
+		anon_vma_chain_free(avc);
+	}
+}
+
 static void anon_vma_ctor(void *data)
 {
 	struct anon_vma *anon_vma = data;
@@ -192,6 +280,7 @@ void __init anon_vma_init(void)
 {
 	anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
 			0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
+	anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
 }
 
 /*
@@ -240,6 +329,18 @@ vma_address(struct page *page, struct vm_area_struct *vma)
 		/* page should be within @vma mapping range */
 		return -EFAULT;
 	}
+	if (unlikely(vma->vm_flags & VM_LOCK_RMAP)) {
+		/*
+		 * This VMA is being unlinked or is not yet linked into the
+		 * VMA tree.  Do not try to follow this rmap.  This race
+		 * condition can result in page_referenced() ignoring a
+		 * reference or in try_to_unmap() failing to unmap a page.
+		 * The VMA cannot be freed under us because we hold the
+		 * anon_vma->lock, which the munmap code takes while
+		 * unlinking the anon_vmas from the VMA.
+		 */
+		return -EFAULT;
+	}
 	return address;
 }
 
@@ -396,7 +497,7 @@ static int page_referenced_anon(struct page *page,
 {
 	unsigned int mapcount;
 	struct anon_vma *anon_vma;
-	struct vm_area_struct *vma;
+	struct anon_vma_chain *avc;
 	int referenced = 0;
 
 	anon_vma = page_lock_anon_vma(page);
@@ -404,7 +505,8 @@ static int page_referenced_anon(struct page *page,
 		return referenced;
 
 	mapcount = page_mapcount(page);
-	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
+		struct vm_area_struct *vma = avc->vma;
 		unsigned long address = vma_address(page, vma);
 		if (address == -EFAULT)
 			continue;
@@ -1025,14 +1127,15 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
 static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
 {
 	struct anon_vma *anon_vma;
-	struct vm_area_struct *vma;
+	struct anon_vma_chain *avc;
 	int ret = SWAP_AGAIN;
 
 	anon_vma = page_lock_anon_vma(page);
 	if (!anon_vma)
 		return ret;
 
-	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
+		struct vm_area_struct *vma = avc->vma;
 		unsigned long address = vma_address(page, vma);
 		if (address == -EFAULT)
 			continue;
@@ -1223,7 +1326,7 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
 		struct vm_area_struct *, unsigned long, void *), void *arg)
 {
 	struct anon_vma *anon_vma;
-	struct vm_area_struct *vma;
+	struct anon_vma_chain *avc;
 	int ret = SWAP_AGAIN;
 
 	/*
@@ -1238,7 +1341,8 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
 	if (!anon_vma)
 		return ret;
 	spin_lock(&anon_vma->lock);
-	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
+		struct vm_area_struct *vma = avc->vma;
 		unsigned long address = vma_address(page, vma);
 		if (address == -EFAULT)
 			continue;