linux-kernel - [PATCH v2 2/2] mm/mmap: remove find_vma_intersection() in vma

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Date: Thu, 25 Jan 2024 11:49:22 +0800
From: Yajun Deng <yajun.deng@...ux.dev>
To: akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com,
	lstoakes@...il.com,
	viro@...iv.linux.org.uk,
	brauner@...nel.org,
	vbabka@...e.cz,
	willy@...radead.org,
	surenb@...gle.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Yajun Deng <yajun.deng@...ux.dev>
Subject: [PATCH v2 2/2] mm/mmap: remove find_vma_intersection() in vma_merge()

We need to find the current vma by find_vma_intersection() in
vma_merge(). Since the src vma was passed, we can add a check to figure
out if the current vma is NULL or the src vma directly.

Remove find_vma_intersection() in vma_merge(). And initialize the next to
NULL when defining it.

Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
---
 mm/mmap.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index f19bc53bc08e..ea02fdc91aa2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -869,7 +869,7 @@ static struct vm_area_struct
 	struct mm_struct *mm = src->vm_mm;
 	struct anon_vma *anon_vma = src->anon_vma;
 	struct file *file = src->vm_file;
-	struct vm_area_struct *curr, *next, *res;
+	struct vm_area_struct *curr = src, *next = NULL, *res;
 	struct vm_area_struct *vma, *adjust, *remove, *remove2;
 	struct vm_area_struct *anon_dup = NULL;
 	struct vma_prepare vp;
@@ -890,14 +890,18 @@ static struct vm_area_struct
 	if (vm_flags & VM_SPECIAL)
 		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 the current vma and the prev vma are the same vma, it
+	 * means the current vma is NULL.
+	 * Does the input range span an existing VMA? (cases 5 - 8)
+	 */
+	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 */
+					/* case 5 set to NULL above */
 
 	if (prev) {
 		vma_start = prev->vm_start;
@@ -921,7 +925,6 @@ 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)
-- 
2.25.1