Re: [PATCH v2 7/8] vdpa_sim: replace the spinlock with a mutex to protect the state

[Jason Wang]

On Tue, Mar 14, 2023 at 1:29 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
> On Thu, Mar 2, 2023 at 7:35 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
> >
> > The spinlock we use to protect the state of the simulator is sometimes
> > held for a long time (for example, when devices handle requests).
> >
> > This also prevents us from calling functions that might sleep (such as
> > kthread_flush_work() in the next patch), and thus having to release
> > and retake the lock.
> >
> > For these reasons, let's replace the spinlock with a mutex that gives
> > us more flexibility.
> >
> > Suggested-by: Jason Wang <jasowang@xxxxxxxxxx>
> > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
>
> Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
>
> Thanks

Btw, though it looks fine but we'd better double confirm virtio_vdpa works well.

(I think so since there's transport that might sleep).

Thanks

>
> > ---
> >  drivers/vdpa/vdpa_sim/vdpa_sim.h     |  4 ++--
> >  drivers/vdpa/vdpa_sim/vdpa_sim.c     | 34 ++++++++++++++--------------
> >  drivers/vdpa/vdpa_sim/vdpa_sim_blk.c |  4 ++--
> >  drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  4 ++--
> >  4 files changed, 23 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> > index ce83f9130a5d..4774292fba8c 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> > @@ -60,8 +60,8 @@ struct vdpasim {
> >         struct kthread_worker *worker;
> >         struct kthread_work work;
> >         struct vdpasim_dev_attr dev_attr;
> > -       /* spinlock to synchronize virtqueue state */
> > -       spinlock_t lock;
> > +       /* mutex to synchronize virtqueue state */
> > +       struct mutex mutex;
> >         /* virtio config according to device type */
> >         void *config;
> >         struct vhost_iotlb *iommu;
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > index 6feb29726c2a..a28103a67ae7 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > @@ -166,7 +166,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
> >         if (IS_ERR(vdpasim->worker))
> >                 goto err_iommu;
> >
> > -       spin_lock_init(&vdpasim->lock);
> > +       mutex_init(&vdpasim->mutex);
> >         spin_lock_init(&vdpasim->iommu_lock);
> >
> >         dev = &vdpasim->vdpa.dev;
> > @@ -275,13 +275,13 @@ static void vdpasim_set_vq_ready(struct vdpa_device *vdpa, u16 idx, bool ready)
> >         struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
> >         bool old_ready;
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >         old_ready = vq->ready;
> >         vq->ready = ready;
> >         if (vq->ready && !old_ready) {
> >                 vdpasim_queue_ready(vdpasim, idx);
> >         }
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >  }
> >
> >  static bool vdpasim_get_vq_ready(struct vdpa_device *vdpa, u16 idx)
> > @@ -299,9 +299,9 @@ static int vdpasim_set_vq_state(struct vdpa_device *vdpa, u16 idx,
> >         struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
> >         struct vringh *vrh = &vq->vring;
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >         vrh->last_avail_idx = state->split.avail_index;
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         return 0;
> >  }
> > @@ -398,9 +398,9 @@ static u8 vdpasim_get_status(struct vdpa_device *vdpa)
> >         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> >         u8 status;
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >         status = vdpasim->status;
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         return status;
> >  }
> > @@ -409,19 +409,19 @@ static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
> >  {
> >         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >         vdpasim->status = status;
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >  }
> >
> >  static int vdpasim_reset(struct vdpa_device *vdpa)
> >  {
> >         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >         vdpasim->status = 0;
> >         vdpasim_do_reset(vdpasim);
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         return 0;
> >  }
> > @@ -430,9 +430,9 @@ static int vdpasim_suspend(struct vdpa_device *vdpa)
> >  {
> >         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >         vdpasim->running = false;
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         return 0;
> >  }
> > @@ -442,7 +442,7 @@ static int vdpasim_resume(struct vdpa_device *vdpa)
> >         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> >         int i;
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >         vdpasim->running = true;
> >
> >         if (vdpasim->pending_kick) {
> > @@ -453,7 +453,7 @@ static int vdpasim_resume(struct vdpa_device *vdpa)
> >                 vdpasim->pending_kick = false;
> >         }
> >
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         return 0;
> >  }
> > @@ -525,14 +525,14 @@ static int vdpasim_set_group_asid(struct vdpa_device *vdpa, unsigned int group,
> >
> >         iommu = &vdpasim->iommu[asid];
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >
> >         for (i = 0; i < vdpasim->dev_attr.nvqs; i++)
> >                 if (vdpasim_get_vq_group(vdpa, i) == group)
> >                         vringh_set_iotlb(&vdpasim->vqs[i].vring, iommu,
> >                                          &vdpasim->iommu_lock);
> >
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         return 0;
> >  }
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > index eb4897c8541e..568119e1553f 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > @@ -290,7 +290,7 @@ static void vdpasim_blk_work(struct vdpasim *vdpasim)
> >         bool reschedule = false;
> >         int i;
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >
> >         if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
> >                 goto out;
> > @@ -321,7 +321,7 @@ static void vdpasim_blk_work(struct vdpasim *vdpasim)
> >                 }
> >         }
> >  out:
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         if (reschedule)
> >                 vdpasim_schedule_work(vdpasim);
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > index e61a9ecbfafe..7ab434592bfe 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > @@ -201,7 +201,7 @@ static void vdpasim_net_work(struct vdpasim *vdpasim)
> >         u64 rx_drops = 0, rx_overruns = 0, rx_errors = 0, tx_errors = 0;
> >         int err;
> >
> > -       spin_lock(&vdpasim->lock);
> > +       mutex_lock(&vdpasim->mutex);
> >
> >         if (!vdpasim->running)
> >                 goto out;
> > @@ -264,7 +264,7 @@ static void vdpasim_net_work(struct vdpasim *vdpasim)
> >         }
> >
> >  out:
> > -       spin_unlock(&vdpasim->lock);
> > +       mutex_unlock(&vdpasim->mutex);
> >
> >         u64_stats_update_begin(&net->tx_stats.syncp);
> >         net->tx_stats.pkts += tx_pkts;
> > --
> > 2.39.2
> >