ring-buffer: Use vma_pages() helper function

Use the vma_pages() helper function and fix the following
Coccinelle/coccicheck warning reported by vma_pages.cocci:

  WARNING: Consider using vma_pages helper on vma

Rename the local variable vma_pages accordingly.

Signed-off-by: Thorsten Blum <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: toblux

kernel/trace/ring_buffer.c

@@ -6920,7 +6920,7 @@ static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,
 static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
 			struct vm_area_struct *vma)
 {
-	unsigned long nr_subbufs, nr_pages, vma_pages, pgoff = vma->vm_pgoff;
+	unsigned long nr_subbufs, nr_pages, nr_vma_pages, pgoff = vma->vm_pgoff;
 	unsigned int subbuf_pages, subbuf_order;
 	struct page **pages;
 	int p = 0, s = 0;
@@ -6946,11 +6946,11 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
 	nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */
 	nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */
 
-	vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
-	if (!vma_pages || vma_pages > nr_pages)
+	nr_vma_pages = vma_pages(vma);
+	if (!nr_vma_pages || nr_vma_pages > nr_pages)
 		return -EINVAL;
 
-	nr_pages = vma_pages;
+	nr_pages = nr_vma_pages;
 
 	pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL);
 	if (!pages)