[Virtio-fs] [PATCH 3/3] virtio-fs: add tracepoints

[Stefan Hajnoczi]

On Mon, Aug 12, 2019 at 05:04:55PM -0400, Masayoshi Mizuma wrote:
> @@ -251,6 +259,11 @@ static void virtio_fs_hiprio_dispatch_work(struct work_struct *work)
>  		notify = virtqueue_kick_prepare(vq);
>  		spin_unlock(&fsvq->lock);
>  
> +		trace_virtio_fs_hiprio_request_dispatched(
> +			forget->ih.opcode, forget->ih.unique,
> +			forget->ih.nodeid, forget->ih.len,
> +			notify);
> +

It is safer to trace the request before placing it in the queue and
before releasing fsvq->lock.  I'm concerned that a fast device may
complete the request and invoke virtio_fs_hiprio_done_work() so that
kfree(req) is called before we've finished tracing it.

(We cannot rely on virtqueue_notify() because devices may poll the
virtqueue, so as soon as the request has been added to the virtqueue it
may be completed.)

> @@ -914,6 +931,10 @@ static int virtio_fs_enqueue_req(struct virtqueue *vq, struct fuse_req *req)
>  
>  	spin_unlock(&fsvq->lock);
>  
> +	trace_virtio_fs_request_dispatched(
> +		req->in.h.opcode, req->in.h.unique,
> +		req->in.h.nodeid, req->in.h.len, req->flags, notify);
> +
>  	if (notify)
>  		virtqueue_notify(vq);

Same here, we no longer control the lifetime of req so it's not safe to
access it after virtqueue_add_sgs() + spin_unlock(&fsvq->lock).
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 488 bytes
Desc: not available
URL: <http://listman.redhat.com/archives/virtio-fs/attachments/20190820/7cf02c81/attachment.sig>