From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38352) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZxBuc-0003lz-CF for qemu-devel@nongnu.org; Fri, 13 Nov 2015 05:48:59 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZxBub-0003No-Dg for qemu-devel@nongnu.org; Fri, 13 Nov 2015 05:48:58 -0500 References: <1447407140-24055-1-git-send-email-famz@redhat.com> From: Laurent Vivier Message-ID: <5645C010.9060104@redhat.com> Date: Fri, 13 Nov 2015 11:48:48 +0100 MIME-Version: 1.0 In-Reply-To: <1447407140-24055-1-git-send-email-famz@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] virtio-blk: Fix double completion for werror=stop List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng , qemu-devel@nongnu.org Cc: Kevin Wolf , qemu-block@nongnu.org, pl@kamp.de, qemu-stable@nongnu.org, Stefan Hajnoczi , dgibson@redhat.com 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-stable@nongnu.org > Signed-off-by: Fam Zheng > --- > 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 In my case, this patch fixes a memory corruption when the VM is stopped on io-error (no space) and restarted.