From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: [PATCH] xen-netback: fix race between napi_complete() and interrupt handler Date: Tue, 25 Mar 2014 14:08:25 +0000 Message-ID: <1395756505-21573-1-git-send-email-david.vrabel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain Cc: , Ian Campbell , Wei Liu , David Vrabel To: Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:15232 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752581AbaCYOKA (ORCPT ); Tue, 25 Mar 2014 10:10:00 -0400 Sender: netdev-owner@vger.kernel.org List-ID: When the NAPI budget was not all used, xenvif_poll() would call napi_complete() /after/ enabling the interrupt. This resulted in a race between the napi_complete() and the napi_schedule() in the interrupt handler. The use of local_irq_save/restore() avoided by race iff the handler is running on the same CPU but not if it was running on a different CPU. Fix this properly by calling napi_complete() before reenabling interrupts (in the xenvif_check_rx_xenvif() call). Signed-off-by: David Vrabel --- drivers/net/xen-netback/interface.c | 28 ++-------------------------- 1 files changed, 2 insertions(+), 26 deletions(-) diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c index 7669d49..ee322d9 100644 --- a/drivers/net/xen-netback/interface.c +++ b/drivers/net/xen-netback/interface.c @@ -65,32 +65,8 @@ static int xenvif_poll(struct napi_struct *napi, int budget) work_done = xenvif_tx_action(vif, budget); if (work_done < budget) { - int more_to_do = 0; - unsigned long flags; - - /* It is necessary to disable IRQ before calling - * RING_HAS_UNCONSUMED_REQUESTS. Otherwise we might - * lose event from the frontend. - * - * Consider: - * RING_HAS_UNCONSUMED_REQUESTS - * - * __napi_complete - * - * This handler is still in scheduled state so the - * event has no effect at all. After __napi_complete - * this handler is descheduled and cannot get - * scheduled again. We lose event in this case and the ring - * will be completely stalled. - */ - - local_irq_save(flags); - - RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do); - if (!more_to_do) - __napi_complete(napi); - - local_irq_restore(flags); + napi_complete(napi); + xenvif_check_rx_xenvif(vif); } return work_done; -- 1.7.2.5