mm: make the vma list be doubly linked

It's a really simple list, and several of the users want to go backwards
in it to find the previous vma.  So rather than have to look up the
previous entry with 'find_vma_prev()' or something similar, just make it
doubly linked instead.

Tested-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 28 insertions, 9 deletions

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index b8bb9a6..ee7e258 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -134,7 +134,7 @@ struct vm_area_struct {
 					   within vm_mm. */
 
 	/* linked list of VM areas per task, sorted by address */
-	struct vm_area_struct *vm_next;
+	struct vm_area_struct *vm_next, *vm_prev;
 
 	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */
 	unsigned long vm_flags;		/* Flags, see mm.h. */
diff --git a/kernel/fork.c b/kernel/fork.c
index 856eac3..b7e9d60 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -300,7 +300,7 @@ out:
 #ifdef CONFIG_MMU
 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 {
-	struct vm_area_struct *mpnt, *tmp, **pprev;
+	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 	struct rb_node **rb_link, *rb_parent;
 	int retval;
 	unsigned long charge;
@@ -328,6 +328,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 	if (retval)
 		goto out;
 
+	prev = NULL;
 	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 		struct file *file;
 
@@ -359,7 +360,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			goto fail_nomem_anon_vma_fork;
 		tmp->vm_flags &= ~VM_LOCKED;
 		tmp->vm_mm = mm;
-		tmp->vm_next = NULL;
+		tmp->vm_next = tmp->vm_prev = NULL;
 		file = tmp->vm_file;
 		if (file) {
 			struct inode *inode = file->f_path.dentry->d_inode;
@@ -392,6 +393,8 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 		 */
 		*pprev = tmp;
 		pprev = &tmp->vm_next;
+		tmp->vm_prev = prev;
+		prev = tmp;
 
 		__vma_link_rb(mm, tmp, rb_link, rb_parent);
 		rb_link = &tmp->vm_rb.rb_right;
diff --git a/mm/mmap.c b/mm/mmap.c
index 3100333..331e51a 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -388,17 +388,23 @@ static inline void
 __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
 		struct vm_area_struct *prev, struct rb_node *rb_parent)
 {
+	struct vm_area_struct *next;
+
+	vma->vm_prev = prev;
 	if (prev) {
-		vma->vm_next = prev->vm_next;
+		next = prev->vm_next;
 		prev->vm_next = vma;
 	} else {
 		mm->mmap = vma;
 		if (rb_parent)
-			vma->vm_next = rb_entry(rb_parent,
+			next = rb_entry(rb_parent,
 					struct vm_area_struct, vm_rb);
 		else
-			vma->vm_next = NULL;
+			next = NULL;
 	}
+	vma->vm_next = next;
+	if (next)
+		next->vm_prev = vma;
 }
 
 void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
@@ -483,7 +489,11 @@ static inline void
 __vma_unlink(struct mm_struct *mm, struct vm_area_struct *vma,
 		struct vm_area_struct *prev)
 {
-	prev->vm_next = vma->vm_next;
+	struct vm_area_struct *next = vma->vm_next;
+
+	prev->vm_next = next;
+	if (next)
+		next->vm_prev = prev;
 	rb_erase(&vma->vm_rb, &mm->mm_rb);
 	if (mm->mmap_cache == vma)
 		mm->mmap_cache = prev;
@@ -1915,6 +1925,7 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
 	unsigned long addr;
 
 	insertion_point = (prev ? &prev->vm_next : &mm->mmap);
+	vma->vm_prev = NULL;
 	do {
 		rb_erase(&vma->vm_rb, &mm->mm_rb);
 		mm->map_count--;
@@ -1922,6 +1933,8 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
 		vma = vma->vm_next;
 	} while (vma && vma->vm_start < end);
 	*insertion_point = vma;
+	if (vma)
+		vma->vm_prev = prev;
 	tail_vma->vm_next = NULL;
 	if (mm->unmap_area == arch_unmap_area)
 		addr = prev ? prev->vm_end : mm->mmap_base;
diff --git a/mm/nommu.c b/mm/nommu.c
index efa9a38..88ff091 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -604,7 +604,7 @@ static void protect_vma(struct vm_area_struct *vma, unsigned long flags)
  */
 static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
 {
-	struct vm_area_struct *pvma, **pp;
+	struct vm_area_struct *pvma, **pp, *next;
 	struct address_space *mapping;
 	struct rb_node **p, *parent;
 
@@ -664,8 +664,11 @@ static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
 			break;
 	}
 
-	vma->vm_next = *pp;
+	next = *pp;
 	*pp = vma;
+	vma->vm_next = next;
+	if (next)
+		next->vm_prev = vma;
 }
 
 /*