On 13/11/2015 10:32, Fam Zheng wrote:
> When a request R is absorbed by request M, it is appended to the
> "mr_next" queue led by M, and is completed together with the completion
> of M, in virtio_blk_rw_complete.
>
> With error policy equals stop, if M has an I/O error, now R also gets
> prepended to the per device DMA restart queue, which will be retried
> when VM resumes. It leads to a double completion (in symptoms of memory
> corruption or use after free).
>
> Adding R to the queue is superfluous, only M needs to be in the queue.
>
> Fix this by marking request R as "merged" and skipping it in
> virtio_blk_handle_rw_error.
>
> Cc: qemu-sta...@nongnu.org
> Signed-off-by: Fam Zheng <f...@redhat.com>
> ---
> hw/block/virtio-blk.c | 9 +++++++--
> include/hw/virtio/virtio-blk.h | 1 +
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index e70fccf..4871f2a 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -36,6 +36,7 @@ VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
> req->in_len = 0;
> req->next = NULL;
> req->mr_next = NULL;
> + req->merged = false;
> return req;
> }
>
> @@ -72,8 +73,11 @@ static int virtio_blk_handle_rw_error(VirtIOBlockReq *req,
> int error,
> VirtIOBlock *s = req->dev;
>
> if (action == BLOCK_ERROR_ACTION_STOP) {
> - req->next = s->rq;
> - s->rq = req;
> + /* Merged requests don't need to be restarted. */
> + if (!req->merged) {
> + req->next = s->rq;
> + s->rq = req;
> + }
> } else if (action == BLOCK_ERROR_ACTION_REPORT) {
> virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
> block_acct_failed(blk_get_stats(s->blk), &req->acct);
> @@ -344,6 +348,7 @@ static inline void submit_requests(BlockBackend *blk,
> MultiReqBuffer *mrb,
> for (i = start + 1; i < start + num_reqs; i++) {
> qemu_iovec_concat(qiov, &mrb->reqs[i]->qiov, 0,
> mrb->reqs[i]->qiov.size);
> + mrb->reqs[i]->merged = true;
> mrb->reqs[i - 1]->mr_next = mrb->reqs[i];
> nb_sectors += mrb->reqs[i]->qiov.size / BDRV_SECTOR_SIZE;
> }
> diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
> index 6bf5905..db4adf4 100644
> --- a/include/hw/virtio/virtio-blk.h
> +++ b/include/hw/virtio/virtio-blk.h
> @@ -70,6 +70,7 @@ typedef struct VirtIOBlockReq {
> size_t in_len;
> struct VirtIOBlockReq *next;
> struct VirtIOBlockReq *mr_next;
> + bool merged;
> BlockAcctCookie acct;
> } VirtIOBlockReq;
>
>
Tested-by: Laurent Vivier <lviv...@redhat.com>
In my case, this patch fixes a memory corruption when the VM is stopped
on io-error (no space) and restarted.
