linux-kernel - [PATCH v3 22/25] virtio_scsi: fix race on device removal

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Date:	Sun, 12 Oct 2014 14:48:22 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org,
	linux-scsi@...r.kernel.org, linux-s390@...r.kernel.org,
	v9fs-developer@...ts.sourceforge.net, netdev@...r.kernel.org,
	kvm@...r.kernel.org, Amit Shah <amit.shah@...hat.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"James E.J. Bottomley" <JBottomley@...allels.com>
Subject: [PATCH v3 22/25] virtio_scsi: fix race on device removal

We cancel event work on device removal, but an interrupt
could trigger immediately after this, and queue it
again.

To fix, set a flag.

Loosely based on patch by Paolo Bonzini

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/scsi/virtio_scsi.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 501838d..327eba0 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;
 
+	/* Protected by event_vq lock */
+	bool stop_events;
+
 	struct virtio_scsi_vq ctrl_vq;
 	struct virtio_scsi_vq event_vq;
 	struct virtio_scsi_vq req_vqs[];
@@ -303,6 +306,11 @@ static void virtscsi_cancel_event_work(struct virtio_scsi *vscsi)
 {
 	int i;
 
+	/* Stop scheduling work before calling cancel_work_sync.  */
+	spin_lock_irq(&vscsi->event_vq.vq_lock);
+	vscsi->stop_events = true;
+	spin_unlock_irq(&vscsi->event_vq.vq_lock);
+
 	for (i = 0; i < VIRTIO_SCSI_EVENT_LEN; i++)
 		cancel_work_sync(&vscsi->event_list[i].work);
 }
@@ -390,7 +398,8 @@ static void virtscsi_complete_event(struct virtio_scsi *vscsi, void *buf)
 {
 	struct virtio_scsi_event_node *event_node = buf;
 
-	queue_work(system_freezable_wq, &event_node->work);
+	if (!vscsi->stop_events)
+		queue_work(system_freezable_wq, &event_node->work);
 }
 
 static void virtscsi_event_done(struct virtqueue *vq)
-- 
MST

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