From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754611AbbAEWLK (ORCPT ); Mon, 5 Jan 2015 17:11:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59771 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751098AbbAEWLI (ORCPT ); Mon, 5 Jan 2015 17:11:08 -0500 Date: Tue, 6 Jan 2015 00:10:59 +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: <20150105221059.GB23518@redhat.com> References: <1420437898-32419-1-git-send-email-famz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > Reviewed-by: Venkatesh Srinivas > > -- vs;