xfs: merge _xfs_buf_get_pages()

Only called from one place now, so merge it into
xfs_buf_alloc_pages(). Because page array allocation is dependent on
bp->b_pages being null, always ensure that when the pages array is
freed we always set bp->b_pages to null.

Also convert the page array to use kmalloc() rather than
kmem_alloc() so we can use the gfp flags we've already calculated
for the allocation context instead of hard coding KM_NOFS semantics.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_buf.c

@@ -272,31 +272,6 @@ _xfs_buf_alloc(
 	return 0;
 }
 
-/*
- *	Allocate a page array capable of holding a specified number
- *	of pages, and point the page buf at it.
- */
-STATIC int
-_xfs_buf_get_pages(
-	struct xfs_buf		*bp,
-	int			page_count)
-{
-	/* Make sure that we have a page list */
-	if (bp->b_pages == NULL) {
-		bp->b_page_count = page_count;
-		if (page_count <= XB_PAGES) {
-			bp->b_pages = bp->b_page_array;
-		} else {
-			bp->b_pages = kmem_alloc(sizeof(struct page *) *
-						 page_count, KM_NOFS);
-			if (bp->b_pages == NULL)
-				return -ENOMEM;
-		}
-		memset(bp->b_pages, 0, sizeof(struct page *) * page_count);
-	}
-	return 0;
-}
-
 /*
  *	Frees b_pages if it was allocated.
  */
@@ -304,10 +279,9 @@ STATIC void
 _xfs_buf_free_pages(
 	struct xfs_buf	*bp)
 {
-	if (bp->b_pages != bp->b_page_array) {
+	if (bp->b_pages != bp->b_page_array)
 		kmem_free(bp->b_pages);
-		bp->b_pages = NULL;
-	}
+	bp->b_pages = NULL;
 }
 
 /*
@@ -389,16 +363,22 @@ xfs_buf_alloc_pages(
 	long		filled = 0;
 	int		error;
 
+	/* Make sure that we have a page list */
+	bp->b_page_count = page_count;
+	if (bp->b_page_count <= XB_PAGES) {
+		bp->b_pages = bp->b_page_array;
+	} else {
+		bp->b_pages = kzalloc(sizeof(struct page *) * bp->b_page_count,
+					gfp_mask);
+		if (!bp->b_pages)
+			return -ENOMEM;
+	}
+	bp->b_flags |= _XBF_PAGES;
+
 	/* Assure zeroed buffer for non-read cases. */
 	if (!(flags & XBF_READ))
 		gfp_mask |= __GFP_ZERO;
 
-	error = _xfs_buf_get_pages(bp, page_count);
-	if (unlikely(error))
-		return error;
-
-	bp->b_flags |= _XBF_PAGES;
-
 	/*
 	 * Bulk filling of pages can take multiple calls. Not filling the entire
 	 * array is not an allocation failure, so don't back off if we get at