From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH RFC] virtio_net: fix refill related races Date: Tue, 20 Dec 2011 21:09:08 +0200 Message-ID: <20111220190908.GC25689@redhat.com> References: <20111207152120.GA23417@redhat.com> <8739cvisqe.fsf@rustcorp.com.au> <20111211144428.GB14381@redhat.com> <878vmioh10.fsf@rustcorp.com.au> <20111212115405.GB7946@redhat.com> <87iplltd0g.fsf@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <87iplltd0g.fsf@rustcorp.com.au> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Rusty Russell Cc: Amit Shah , netdev@vger.kernel.org, Tejun Heo , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Tue, Dec 13, 2011 at 01:05:11PM +1030, Rusty Russell wrote: > On Mon, 12 Dec 2011 13:54:06 +0200, "Michael S. Tsirkin" wrote: > > On Mon, Dec 12, 2011 at 09:25:07AM +1030, Rusty Russell wrote: > > > Orthogonally, the refill-stop code is still buggy, as you noted. > > > > Sorry I don't understand how it's still buggy. > > Both places where we call: > > cancel_delayed_work_sync(&vi->refill); > > Do not actually guarantee that vi->refill isn't running, because it > can requeue itself. A 'bool no_more_refill' field seems like the > simplest fix for this, but I don't think it's sufficient. > > Tejun, is this correct? What's the correct way to synchronously stop a > delayed_work which can "schedule_delayed_work(&vi->refill, HZ/2);" on > itself? > > Thanks, > Rusty. Another question, wanted to make sure: virtnet_poll does schedule_delayed_work(&vi->refill, 0); separately refill work itself also does schedule_delayed_work(&vi->refill, HZ/2); If two such events happen twice, on different CPUs, we are still guaranteed the work will only run once, right? From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752603Ab1LTTHY (ORCPT ); Tue, 20 Dec 2011 14:07:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52656 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751643Ab1LTTHS (ORCPT ); Tue, 20 Dec 2011 14:07:18 -0500 Date: Tue, 20 Dec 2011 21:09:08 +0200 From: "Michael S. Tsirkin" To: Rusty Russell Cc: Amit Shah , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: Re: [PATCH RFC] virtio_net: fix refill related races Message-ID: <20111220190908.GC25689@redhat.com> References: <20111207152120.GA23417@redhat.com> <8739cvisqe.fsf@rustcorp.com.au> <20111211144428.GB14381@redhat.com> <878vmioh10.fsf@rustcorp.com.au> <20111212115405.GB7946@redhat.com> <87iplltd0g.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87iplltd0g.fsf@rustcorp.com.au> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 13, 2011 at 01:05:11PM +1030, Rusty Russell wrote: > On Mon, 12 Dec 2011 13:54:06 +0200, "Michael S. Tsirkin" wrote: > > On Mon, Dec 12, 2011 at 09:25:07AM +1030, Rusty Russell wrote: > > > Orthogonally, the refill-stop code is still buggy, as you noted. > > > > Sorry I don't understand how it's still buggy. > > Both places where we call: > > cancel_delayed_work_sync(&vi->refill); > > Do not actually guarantee that vi->refill isn't running, because it > can requeue itself. A 'bool no_more_refill' field seems like the > simplest fix for this, but I don't think it's sufficient. > > Tejun, is this correct? What's the correct way to synchronously stop a > delayed_work which can "schedule_delayed_work(&vi->refill, HZ/2);" on > itself? > > Thanks, > Rusty. Another question, wanted to make sure: virtnet_poll does schedule_delayed_work(&vi->refill, 0); separately refill work itself also does schedule_delayed_work(&vi->refill, HZ/2); If two such events happen twice, on different CPUs, we are still guaranteed the work will only run once, right?