Re: [PATCH 1/5] virtiofs: Do not end request in submission context

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Oct 21, 2019 at 10:03:39AM +0200, Miklos Szeredi wrote:

[..]
> >  static void virtio_fs_hiprio_dispatch_work(struct work_struct *work)
> > @@ -502,6 +522,7 @@ static int virtio_fs_setup_vqs(struct virtio_device *vdev,
> >         names[VQ_HIPRIO] = fs->vqs[VQ_HIPRIO].name;
> >         INIT_WORK(&fs->vqs[VQ_HIPRIO].done_work, virtio_fs_hiprio_done_work);
> >         INIT_LIST_HEAD(&fs->vqs[VQ_HIPRIO].queued_reqs);
> > +       INIT_LIST_HEAD(&fs->vqs[VQ_HIPRIO].end_reqs);
> >         INIT_DELAYED_WORK(&fs->vqs[VQ_HIPRIO].dispatch_work,
> >                         virtio_fs_hiprio_dispatch_work);
> >         spin_lock_init(&fs->vqs[VQ_HIPRIO].lock);
> > @@ -511,8 +532,9 @@ static int virtio_fs_setup_vqs(struct virtio_device *vdev,
> >                 spin_lock_init(&fs->vqs[i].lock);
> >                 INIT_WORK(&fs->vqs[i].done_work, virtio_fs_requests_done_work);
> >                 INIT_DELAYED_WORK(&fs->vqs[i].dispatch_work,
> > -                                       virtio_fs_dummy_dispatch_work);
> > +                                 virtio_fs_request_dispatch_work);
> >                 INIT_LIST_HEAD(&fs->vqs[i].queued_reqs);
> > +               INIT_LIST_HEAD(&fs->vqs[i].end_reqs);
> >                 snprintf(fs->vqs[i].name, sizeof(fs->vqs[i].name),
> >                          "requests.%u", i - VQ_REQUEST);
> >                 callbacks[i] = virtio_fs_vq_done;
> > @@ -918,6 +940,7 @@ __releases(fiq->lock)
> >         struct fuse_conn *fc;
> >         struct fuse_req *req;
> >         struct fuse_pqueue *fpq;
> > +       struct virtio_fs_vq *fsvq;
> >         int ret;
> >
> >         WARN_ON(list_empty(&fiq->pending));
> > @@ -951,7 +974,8 @@ __releases(fiq->lock)
> >         smp_mb__after_atomic();
> >
> >  retry:
> > -       ret = virtio_fs_enqueue_req(&fs->vqs[queue_id], req);
> > +       fsvq = &fs->vqs[queue_id];
> > +       ret = virtio_fs_enqueue_req(fsvq, req);
> >         if (ret < 0) {
> >                 if (ret == -ENOMEM || ret == -ENOSPC) {
> >                         /* Virtqueue full. Retry submission */
> > @@ -965,7 +989,13 @@ __releases(fiq->lock)
> >                 clear_bit(FR_SENT, &req->flags);
> >                 list_del_init(&req->list);
> >                 spin_unlock(&fpq->lock);
> > -               fuse_request_end(fc, req);
> > +
> > +               /* Can't end request in submission context. Use a worker */
> > +               spin_lock(&fsvq->lock);
> > +               list_add_tail(&req->list, &fsvq->end_reqs);
> > +               schedule_delayed_work(&fsvq->dispatch_work,
> > +                                     msecs_to_jiffies(1));
> 
> What's the reason to delay by one msec?  If this is purely for
> deadlock avoidance, then a zero delay would work better, no?

Hi Miklos,

I have no good reason to do that. Will change it to zero delay.

Thanks
Vivek