From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754484AbbAFHQF (ORCPT ); Tue, 6 Jan 2015 02:16:05 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41025 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752383AbbAFHQB (ORCPT ); Tue, 6 Jan 2015 02:16:01 -0500 Date: Tue, 6 Jan 2015 09:15:49 +0200 From: "Michael S. Tsirkin" To: Venkatesh Srinivas Cc: Fam Zheng , linux-scsi@vger.kernel.org, "James E.J. Bottomley" , Linux Kernel Developers List , Paolo Bonzini , Christoph Hellwig Subject: Re: [PATCH] virtio-scsi: Fix the race condition in virtscsi_handle_event Message-ID: <20150106071549.GA29433@redhat.com> References: <1420437898-32419-1-git-send-email-famz@redhat.com> <20150105221059.GB23518@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20150105221059.GB23518@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 06, 2015 at 12:10:59AM +0200, Michael S. Tsirkin wrote: > On Mon, Jan 05, 2015 at 11:48:47AM -0800, Venkatesh Srinivas wrote: > > On Sun, Jan 4, 2015 at 10:04 PM, Fam Zheng wrote: > > > > There is a race condition in virtscsi_handle_event, when many device > > hotplug/unplug events flush in quickly. > > > > The scsi_remove_device in virtscsi_handle_transport_reset may trigger > > the BUG_ON in scsi_target_reap, because the state is altered behind it, > > probably by scsi_scan_host of another event. I'm able to reproduce it by > > repeatedly plugging and unplugging a scsi disk with the same lun number. > > > > To make is safe, the mutex added in struct virtio_scsi is held in > > virtscsi_handle_event, so that all the events are processed in a > > synchronized way. With this lock, the panic goes away. > > > > Signed-off-by: Fam Zheng > > --- > >  drivers/scsi/virtio_scsi.c | 6 ++++++ > >  1 file changed, 6 insertions(+) > > > > diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c > > index c52bb5d..7f194d4 100644 > > --- a/drivers/scsi/virtio_scsi.c > > +++ b/drivers/scsi/virtio_scsi.c > > @@ -110,6 +110,9 @@ struct virtio_scsi { > >         /* CPU hotplug notifier */ > >         struct notifier_block nb; > > > > +       /* Protect the hotplug/unplug event handling */ > > +       struct mutex scan_lock; > > + > >         /* Protected by event_vq lock */ > >         bool stop_events; > > > > @@ -377,6 +380,7 @@ static void virtscsi_handle_event(struct work_struct > > *work) > >         struct virtio_scsi *vscsi = event_node->vscsi; > >         struct virtio_scsi_event *event = &event_node->event; > > > > +       mutex_lock(&vscsi->scan_lock); > >         if (event->event & > >             cpu_to_virtio32(vscsi->vdev, VIRTIO_SCSI_T_EVENTS_MISSED)) { > >                 event->event &= ~cpu_to_virtio32(vscsi->vdev, > > @@ -397,6 +401,7 @@ static void virtscsi_handle_event(struct work_struct > > *work) > >                 pr_err("Unsupport virtio scsi event %x\n", event->event); > >         } > >         virtscsi_kick_event(vscsi, event_node); > > +       mutex_unlock(&vscsi->scan_lock); > >  } > > > >  static void virtscsi_complete_event(struct virtio_scsi *vscsi, void *buf) > > @@ -894,6 +899,7 @@ static int virtscsi_init(struct virtio_device *vdev, > >         const char **names; > >         struct virtqueue **vqs; > > > > +       mutex_init(&vscsi->scan_lock); > >         num_vqs = vscsi->num_queues + VIRTIO_SCSI_VQ_BASE; > >         vqs = kmalloc(num_vqs * sizeof(struct virtqueue *), GFP_KERNEL); > >         callbacks = kmalloc(num_vqs * sizeof(vq_callback_t *), GFP_KERNEL); > > -- > > 1.9.3 > > > > > > Nice find. > > > > This fix does have the effect of serializing all event handling via scan_lock; > > perhaps you want to instead create a singlethreaded workqueue in virtio_scsi > > and queue handle_event there, rather than waiting on scan_lock on the system > > workqueue? > > Or use the system single-threaded wq. I was sure we have one, but apparently not :( Pls ignore the comment, sorry about the noise. > > > Reviewed-by: Venkatesh Srinivas > > > > -- vs;