It took a few days but last night the problem was reproduced.
This is the information from the log:
vdev 0x55f261d940f0 ("virtio-blk")
vq 0x55f261d9ee40 (idx 0)
inuse 128 vring.num 128
old_shadow_avail_idx 58874 last_avail_idx 58625 avail_idx 58874
avail 0x3d87a800 avail_idx (cache bypassed) 58625
used_idx 58497
2019-02-18 03:20:08.605+0000: shutting down, reason=crashed
The dump file, including guest memory, was generated successfully (after gzip
the file is around 492MB).
I switched the guest now to virtio-scsi to get the information and dump with
this setup as well.
How should we proceed?
Thanks.
On lun, feb 11, 2019 at 4:17 AM, Stefan Hajnoczi <stefa...@gmail.com> wrote:
Thanks for collecting the data! The fact that both virtio-blk and virtio-scsi
failed suggests it's not a virtqueue element leak in the virtio-blk or
virtio-scsi device emulation code. The hung task error messages from inside the
guest are a consequence of QEMU hitting the "Virtqueue size exceeded" error.
QEMU refuses to process further requests after the error, causing tasks inside
the guest to get stuck on I/O. I don't have a good theory regarding the root
cause. Two ideas: 1. The guest is corrupting the vring or submitting more
requests than will fit into the ring. Somewhat unlikely because it happens with
both Windows and Linux guests. 2. QEMU's virtqueue code is buggy, maybe the
memory region cache which is used for fast guest RAM accesses. Here is an
expanded version of the debug patch which might help identify which of these
scenarios is likely. Sorry, it requires running the guest again! This time
let's make QEMU dump core so both QEMU state and guest RAM are captured for
further debugging. That way it will be possible to extract more information
using gdb without rerunning. Stefan --- diff --git a/hw/virtio/virtio.c
b/hw/virtio/virtio.c index a1ff647a66..28d89fcbcb 100644 ---
a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -866,6 +866,7 @@ void
*virtqueue_pop(VirtQueue *vq, size_t sz) return NULL; } rcu_read_lock(); +
uint16_t old_shadow_avail_idx = vq->shadow_avail_idx; if
(virtio_queue_empty_rcu(vq)) { goto done; } @@ -879,6 +880,12 @@ void
*virtqueue_pop(VirtQueue *vq, size_t sz) max = vq->vring.num; if (vq->inuse >=
vq->vring.num) { + fprintf(stderr, "vdev %p (\"%s\")\n", vdev, vdev->name); +
fprintf(stderr, "vq %p (idx %u)\n", vq, (unsigned int)(vq - vdev->vq)); +
fprintf(stderr, "inuse %u vring.num %u\n", vq->inuse, vq->vring.num); +
fprintf(stderr, "old_shadow_avail_idx %u last_avail_idx %u avail_idx %u\n",
old_shadow_avail_idx, vq->last_avail_idx, vq->shadow_avail_idx); +
fprintf(stderr, "avail %#" HWADDR_PRIx " avail_idx (cache bypassed) %u\n",
vq->vring.avail, virtio_lduw_phys(vdev, vq->vring.avail + offsetof(VRingAvail,
idx))); + fprintf(stderr, "used_idx %u\n", vq->used_idx); + abort(); /* <---
core dump! */ virtio_error(vdev, "Virtqueue size exceeded"); goto done; }
