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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index a33048ee9621a360060fed128d6f048faf53ea42..01660c595f5c3e7e4a8470228fbf04699b690e9c 100644 (file)
--- 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;
 }