From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH v2 net 1/5] fm10k: fix race accessing page->_count Date: Fri, 10 Oct 2014 04:48:14 -0700 Message-ID: <1412941698-17502-2-git-send-email-edumazet@google.com> References: <1412941698-17502-1-git-send-email-edumazet@google.com> Cc: netdev@vger.kernel.org, Alexander Duyck , Jeff Kirsher , Andres Lagar-Cavilla , Greg Thelen , Hugh Dickins , David Rientjes , Eric Dumazet To: "David S. Miller" Return-path: Received: from mail-ig0-f202.google.com ([209.85.213.202]:42892 "EHLO mail-ig0-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751579AbaJJLs3 (ORCPT ); Fri, 10 Oct 2014 07:48:29 -0400 Received: by mail-ig0-f202.google.com with SMTP id r10so369179igi.1 for ; Fri, 10 Oct 2014 04:48:28 -0700 (PDT) In-Reply-To: <1412941698-17502-1-git-send-email-edumazet@google.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 Acked-by: Jeff Kirsher --- drivers/net/ethernet/intel/fm10k/fm10k_main.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/drivers/net/ethernet/intel/fm10k/fm10k_main.c b/drivers/net/ethernet/intel/fm10k/fm10k_main.c index 6c800a330d66..9d7118a0d67a 100644 --- a/drivers/net/ethernet/intel/fm10k/fm10k_main.c +++ b/drivers/net/ethernet/intel/fm10k/fm10k_main.c @@ -219,11 +219,10 @@ static bool fm10k_can_reuse_rx_page(struct fm10k_rx_buffer *rx_buffer, /* flip page offset to other buffer */ rx_buffer->page_offset ^= FM10K_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; -- 2.1.0.rc2.206.gedb03e5