From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-2.mimecast.com ([207.211.31.81]:24047 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731794AbgFSLkP (ORCPT ); Fri, 19 Jun 2020 07:40:15 -0400 Date: Fri, 19 Jun 2020 13:40:05 +0200 From: Cornelia Huck Subject: Re: [RFC PATCH v3 3/3] vfio-ccw: Check workqueue before doing START Message-ID: <20200619134005.512fc54f.cohuck@redhat.com> In-Reply-To: <20200616195053.99253-4-farman@linux.ibm.com> References: <20200616195053.99253-1-farman@linux.ibm.com> <20200616195053.99253-4-farman@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Eric Farman Cc: Jared Rossi , Halil Pasic , linux-s390@vger.kernel.org, kvm@vger.kernel.org On Tue, 16 Jun 2020 21:50:53 +0200 Eric Farman wrote: > When an interrupt is received via the IRQ, the bulk of the work is > stacked on a workqueue for later processing. Which means that concurrent > START or a HALT/CLEAR operation (via the async_region) will race with > this process and require some serialization. > > Once we have all our locks acquired, let's just look to see if we're > in a window where the process has been started from the IRQ, but not > yet picked up by vfio-ccw to clean up an I/O. If there is, mark the > request as BUSY so it can be redriven after we have a chance to breathe. This change looks reasonable to me. It would be even better if we could send off I/O requests at any time; but if signaling to retry saves us from some hairy code elsewhere, it is a good idea to do so. > > Signed-off-by: Eric Farman > --- > drivers/s390/cio/vfio_ccw_fsm.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c > index f0952192480e..9dc5b4d549b3 100644 > --- a/drivers/s390/cio/vfio_ccw_fsm.c > +++ b/drivers/s390/cio/vfio_ccw_fsm.c > @@ -28,6 +28,11 @@ static int fsm_io_helper(struct vfio_ccw_private *private) > > spin_lock_irqsave(sch->lock, flags); > > + if (work_pending(&private->io_work)) { > + ret = -EBUSY; > + goto out; > + } > + > orb = cp_get_orb(&private->cp, (u32)(addr_t)sch, sch->lpm); > if (!orb) { > ret = -EIO;