mm/mremap: remove goto from mremap_to()

mremap_to() has a goto label at the end that doesn't unwind anything. 
Removing the label makes the code cleaner.

This commit also adds documentation to the function.

Link: https://lkml.kernel.org/r/20241018174114.2871880-3-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Pedro Falcato <pedro.falcato@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mremap.c

@@ -887,6 +887,20 @@ static int resize_is_valid(struct vm_area_struct *vma, unsigned long addr,
 	return 0;
 }
 
+/*
+ * mremap_to() - remap a vma to a new location
+ * @addr: The old address
+ * @old_len: The old size
+ * @new_addr: The target address
+ * @new_len: The new size
+ * @locked: If the returned vma is locked (VM_LOCKED)
+ * @flags: the mremap flags
+ * @uf: The mremap userfaultfd context
+ * @uf_unmap_early: The userfaultfd unmap early context
+ * @uf_unmap: The userfaultfd unmap context
+ *
+ * Returns: The new address of the vma or an error.
+ */
 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 		unsigned long new_addr, unsigned long new_len, bool *locked,
 		unsigned long flags, struct vm_userfaultfd_ctx *uf,
@@ -895,18 +909,18 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
-	unsigned long ret = -EINVAL;
+	unsigned long ret;
 	unsigned long map_flags = 0;
 
 	if (offset_in_page(new_addr))
-		goto out;
+		return -EINVAL;
 
 	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
-		goto out;
+		return -EINVAL;
 
 	/* Ensure the old/new locations do not overlap */
 	if (addr + old_len > new_addr && new_addr + new_len > addr)
-		goto out;
+		return -EINVAL;
 
 	/*
 	 * move_vma() need us to stay 4 maps below the threshold, otherwise
@@ -933,31 +947,28 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 		 */
 		ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 		if (ret)
-			goto out;
+			return ret;
 	}
 
 	if (old_len > new_len) {
 		ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 		if (ret)
-			goto out;
+			return ret;
 		old_len = new_len;
 	}
 
 	vma = vma_lookup(mm, addr);
-	if (!vma) {
-		ret = -EFAULT;
-		goto out;
-	}
+	if (!vma)
+		return -EFAULT;
 
 	ret = resize_is_valid(vma, addr, old_len, new_len, flags);
 	if (ret)
-		goto out;
+		return ret;
 
 	/* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 	if (flags & MREMAP_DONTUNMAP &&
 		!may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
-		ret = -ENOMEM;
-		goto out;
+		return -ENOMEM;
 	}
 
 	if (flags & MREMAP_FIXED)
@@ -970,17 +981,14 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 				((addr - vma->vm_start) >> PAGE_SHIFT),
 				map_flags);
 	if (IS_ERR_VALUE(ret))
-		goto out;
+		return ret;
 
 	/* We got a new mapping */
 	if (!(flags & MREMAP_FIXED))
 		new_addr = ret;
 
-	ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
-		       uf_unmap);
-
-out:
-	return ret;
+	return move_vma(vma, addr, old_len, new_len, new_addr, locked, flags,
+			uf, uf_unmap);
 }
 
 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)