From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pekka Enberg Subject: Re: [PATCH 1/3] kvm tools: Make virtio-net kvm__irq_line thread safe Date: Fri, 29 Apr 2011 20:43:41 +0300 Message-ID: References: <1304058985-13833-1-git-send-email-asias.hejun@gmail.com> <20110429073006.GB16371@elte.hu> <4DBA6CFE.5090400@gmail.com> <20110429103210.GB24217@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Asias He , Cyrill Gorcunov , Sasha Levin , Prasad Joshi , kvm@vger.kernel.org To: Ingo Molnar Return-path: Received: from mail-vw0-f46.google.com ([209.85.212.46]:45035 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760678Ab1D2Rnm (ORCPT ); Fri, 29 Apr 2011 13:43:42 -0400 Received: by vws1 with SMTP id 1so2922309vws.19 for ; Fri, 29 Apr 2011 10:43:41 -0700 (PDT) In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Apr 29, 2011 at 1:32 PM, Ingo Molnar wrote: >>> Without the mutex around the kvm__irq_line, I am still seeing the >>> hangs(with the irq assertion movement patch). >> >> since the mutex has no effect on the other party that modifies the virtual >> queue (the guest OS), this at best only changes timings and hides the bug. On Fri, Apr 29, 2011 at 1:42 PM, Pekka Enberg wrote: > Yes, I don't think it has anything to do with the queues - it's simply > a bug in the RX path which requires other work to happen to raise the > IRQ. Turns out thread pool isn't related to the problem. Asias and Sasha reported that the problem triggers even with all the thread pool code reverted. I'm guessing it's a latent bug in the virtio network driver that got exposed by Cyrill's patch. It seems to be related to IRQ handling and I still think it's related to assuming VIRTIO_PCI_QUEUE_NOTIFY will be triggered for the RX path. Pekka