diff mbox series

[v3,QEMU,2/3] virtio-balloon: Add locking to prevent possible race when starting hinting

Message ID 20200720175122.21935.78013.stgit@localhost.localdomain (mailing list archive)
State New, archived
Headers show
Series virtio-balloon: Free page hinting clean-ups | expand

Commit Message

Alexander Duyck July 20, 2020, 5:51 p.m. UTC 
From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

There is already locking in place when we are stopping free page hinting
but there is not similar protections in place when we start. I can only
assume this was overlooked as in most cases the page hinting should not be
occurring when we are starting the hinting, however there is still a chance
we could be processing hints by the time we get back around to restarting
the hinting so we are better off making sure to protect the state with the
mutex lock rather than just updating the value with no protections.

Based on feedback from Peter Maydell this issue had also been spotted by
Coverity: CID 1430269

Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 hw/virtio/virtio-balloon.c |    4 ++++
 1 file changed, 4 insertions(+)
diff mbox series

Patch

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index ce70adcc6925..6e2d1293402f 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -592,6 +592,8 @@  static void virtio_balloon_free_page_start(VirtIOBalloon *s)
         return;
     }
 
+    qemu_mutex_lock(&s->free_page_lock);
+
     if (s->free_page_report_cmd_id == UINT_MAX) {
         s->free_page_report_cmd_id =
                        VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
@@ -600,6 +602,8 @@  static void virtio_balloon_free_page_start(VirtIOBalloon *s)
     }
 
     s->free_page_report_status = FREE_PAGE_REPORT_S_REQUESTED;
+    qemu_mutex_unlock(&s->free_page_lock);
+
     virtio_notify_config(vdev);
 }