From 7eb63fccf4cc533249bde484daba6e40264d74f9 Mon Sep 17 00:00:00 2001 From: Alexander Duyck Date: Mon, 20 Jul 2020 10:51:22 -0700 Subject: [PATCH] virtio-balloon: Add locking to prevent possible race when starting hinting 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 Signed-off-by: Alexander Duyck Message-Id: <20200720175122.21935.78013.stgit@localhost.localdomain> Cc: qemu-stable@nongnu.org Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin (cherry picked from commit 1a83e0b9c492a0eaeacd6fbb858fc81d04ab9c3e) Signed-off-by: Michael Roth --- hw/virtio/virtio-balloon.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index a30a0c7bfa..d6e31de1d9 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -532,6 +532,8 @@ 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; @@ -540,6 +542,8 @@ 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); } -- 2.39.5