ixgbe: fix race accessing page->_count

This is illegal to use atomic_set(&page->_count, 2) 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>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index d677b5a..fec5212 100644 (file)
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1865,12 +1865,10 @@ static bool ixgbe_add_rx_frag(struct ixgbe_ring *rx_ring,
        /* flip page offset to other buffer */
        rx_buffer->page_offset ^= truesize;
 
-       /*
-        * since we are the only owner of the page and we need to
-        * increment it, just set the value to 2 in order to avoid
-        * an unecessary locked operation
+       /* Even if we own the page, we are not allowed to use atomic_set()
+        * This would break get_page_unless_zero() users.
         */
-       atomic_set(&page->_count, 2);
+       atomic_inc(&page->_count);
 #else
        /* move offset up to the next cache line */
        rx_buffer->page_offset += truesize;