igb: 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/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index ae59c0b..a21b144 100644 (file)
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -6545,11 +6545,10 @@ static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,
        /* flip page offset to other buffer */
        rx_buffer->page_offset ^= IGB_RX_BUFSZ;
 
-       /* 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 unnecessary 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;