mlx4: fix race accessing page->_count

This is illegal to use atomic_set(&page->_count, ...) even if we 'own' the page. Other entities in the kernel need to use get_page_unless_zero() to get a reference to the page before testing page properties, so we could loose a refcount increment. Signed-off-by: Eric Dumazet <[email protected]> Signed-off-by: David S. Miller <[email protected]>
chewitt · Oct 10, 2014 · 9822620 · 9822620
1 parent ec91698
commit 9822620
Showing 1 changed file with 3 additions and 3 deletions.
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
@@ -76,10 +76,10 @@ static int mlx4_alloc_pages(struct mlx4_en_priv *priv,
 	page_alloc->dma = dma;
 	page_alloc->page_offset = frag_info->frag_align;
 	/* Not doing get_page() for each frag is a big win
-	 * on asymetric workloads.
+	 * on asymetric workloads. Note we can not use atomic_set().
 	 */
-	atomic_set(&page->_count,
-		   page_alloc->page_size / frag_info->frag_stride);
+	atomic_add(page_alloc->page_size / frag_info->frag_stride - 1,
+		   &page->_count);
 	return 0;
 }