[PATCH] mm/mmap: simplify vma_merge()

[Yajun Deng <yajun.deng@linux.dev>]

These vma_merge() callers will pass mm, anon_vma and file, they all from
vma. There is no need to pass three parameters at the same time.

We will find the current vma in vma_merge(). If we pass the original vma
to vma_merge(), the current vma is actually the original vma or NULL.
So we didn't need to find the current vma with find_vma_intersection().

Pass vma to vma_merge(), and add a check to make sure the current vma
is an existing vma.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
 mm/mmap.c | 37 +++++++++++++++++--------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 49d25172eac8..7e00ae4f39e3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -860,14 +860,16 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
  *      area is returned, or the function will return NULL
  */
 static struct vm_area_struct
-*vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
-	   struct vm_area_struct *prev, unsigned long addr, unsigned long end,
-	   unsigned long vm_flags, struct anon_vma *anon_vma, struct file *file,
-	   pgoff_t pgoff, struct mempolicy *policy,
+*vma_merge(struct vma_iterator *vmi, struct vm_area_struct *prev,
+	   struct vm_area_struct *curr, unsigned long addr, unsigned long end,
+	   unsigned long vm_flags, pgoff_t pgoff, struct mempolicy *policy,
 	   struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
 	   struct anon_vma_name *anon_name)
 {
-	struct vm_area_struct *curr, *next, *res;
+	struct mm_struct *mm = curr->vm_mm;
+	struct anon_vma *anon_vma = curr->anon_vma;
+	struct file *file = curr->vm_file;
+	struct vm_area_struct *next = NULL, *res;
 	struct vm_area_struct *vma, *adjust, *remove, *remove2;
 	struct vm_area_struct *anon_dup = NULL;
 	struct vma_prepare vp;
@@ -889,13 +891,12 @@ static struct vm_area_struct
 		return NULL;
 
 	/* Does the input range span an existing VMA? (cases 5 - 8) */
-	curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);
+	if (prev == curr || addr != curr->vm_start || end > curr->vm_end)
+		curr = NULL;
 
 	if (!curr ||			/* cases 1 - 4 */
 	    end == curr->vm_end)	/* cases 6 - 8, adjacent VMA */
-		next = vma_lookup(mm, end);
-	else
-		next = NULL;		/* case 5 */
+		next = vma_lookup(mm, end); /* NULL case 5 */
 
 	if (prev) {
 		vma_start = prev->vm_start;
@@ -919,7 +920,6 @@ static struct vm_area_struct
 
 	/* Verify some invariant that must be enforced by the caller. */
 	VM_WARN_ON(prev && addr <= prev->vm_start);
-	VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));
 	VM_WARN_ON(addr >= end);
 
 	if (!merge_prev && !merge_next)
@@ -2424,9 +2424,8 @@ struct vm_area_struct *vma_modify(struct vma_iterator *vmi,
 	pgoff_t pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 	struct vm_area_struct *merged;
 
-	merged = vma_merge(vmi, vma->vm_mm, prev, start, end, vm_flags,
-			   vma->anon_vma, vma->vm_file, pgoff, policy,
-			   uffd_ctx, anon_name);
+	merged = vma_merge(vmi, prev, vma, start, end, vm_flags,
+			   pgoff, policy, uffd_ctx, anon_name);
 	if (merged)
 		return merged;
 
@@ -2456,9 +2455,8 @@ static struct vm_area_struct
 		   struct vm_area_struct *vma, unsigned long start,
 		   unsigned long end, pgoff_t pgoff)
 {
-	return vma_merge(vmi, vma->vm_mm, prev, start, end, vma->vm_flags,
-			 vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
-			 vma->vm_userfaultfd_ctx, anon_vma_name(vma));
+	return vma_merge(vmi, prev, vma, start, end, vma->vm_flags, pgoff,
+			 vma_policy(vma), vma->vm_userfaultfd_ctx, anon_vma_name(vma));
 }
 
 /*
@@ -2472,10 +2470,9 @@ struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
 	pgoff_t pgoff = vma->vm_pgoff + vma_pages(vma);
 
 	/* vma is specified as prev, so case 1 or 2 will apply. */
-	return vma_merge(vmi, vma->vm_mm, vma, vma->vm_end, vma->vm_end + delta,
-			 vma->vm_flags, vma->anon_vma, vma->vm_file, pgoff,
-			 vma_policy(vma), vma->vm_userfaultfd_ctx,
-			 anon_vma_name(vma));
+	return vma_merge(vmi, vma, vma, vma->vm_end, vma->vm_end + delta,
+			 vma->vm_flags, pgoff, vma_policy(vma),
+			 vma->vm_userfaultfd_ctx, anon_vma_name(vma));
 }
 
 /*
-- 
2.25.1