netdev - Re: [PATCH net-next v6 1/4] net: vhost: lock the vqs one by one

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Message-ID: <CAMDZJNX41vtdNNEAxHYwC+WcrJFkON70hVumVE9rbFDBC5QUOQ@mail.gmail.com>
Date:   Wed, 25 Jul 2018 20:05:56 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     mst@...hat.com
Cc:     jasowang@...hat.com, makita.toshiaki@....ntt.co.jp,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v6 1/4] net: vhost: lock the vqs one by one

On Sun, Jul 22, 2018 at 11:26 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Sat, Jul 21, 2018 at 11:03:59AM -0700, xiangxia.m.yue@...il.com wrote:
> > From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> >
> > This patch changes the way that lock all vqs
> > at the same, to lock them one by one. It will
> > be used for next patch to avoid the deadlock.
> >
> > Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> > Acked-by: Jason Wang <jasowang@...hat.com>
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > ---
> >  drivers/vhost/vhost.c | 24 +++++++-----------------
> >  1 file changed, 7 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index a502f1a..a1c06e7 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -294,8 +294,11 @@ static void vhost_vq_meta_reset(struct vhost_dev *d)
> >  {
> >       int i;
> >
> > -     for (i = 0; i < d->nvqs; ++i)
> > +     for (i = 0; i < d->nvqs; ++i) {
> > +             mutex_lock(&d->vqs[i]->mutex);
> >               __vhost_vq_meta_reset(d->vqs[i]);
> > +             mutex_unlock(&d->vqs[i]->mutex);
> > +     }
> >  }
> >
> >  static void vhost_vq_reset(struct vhost_dev *dev,
> > @@ -890,20 +893,6 @@ static inline void __user *__vhost_get_user(struct vhost_virtqueue *vq,
> >  #define vhost_get_used(vq, x, ptr) \
> >       vhost_get_user(vq, x, ptr, VHOST_ADDR_USED)
> >
> > -static void vhost_dev_lock_vqs(struct vhost_dev *d)
> > -{
> > -     int i = 0;
> > -     for (i = 0; i < d->nvqs; ++i)
> > -             mutex_lock_nested(&d->vqs[i]->mutex, i);
> > -}
> > -
> > -static void vhost_dev_unlock_vqs(struct vhost_dev *d)
> > -{
> > -     int i = 0;
> > -     for (i = 0; i < d->nvqs; ++i)
> > -             mutex_unlock(&d->vqs[i]->mutex);
> > -}
> > -
> >  static int vhost_new_umem_range(struct vhost_umem *umem,
> >                               u64 start, u64 size, u64 end,
> >                               u64 userspace_addr, int perm)
> > @@ -953,7 +942,10 @@ static void vhost_iotlb_notify_vq(struct vhost_dev *d,
> >               if (msg->iova <= vq_msg->iova &&
> >                   msg->iova + msg->size - 1 > vq_msg->iova &&
> >                   vq_msg->type == VHOST_IOTLB_MISS) {
> > +                     mutex_lock(&node->vq->mutex);
> >                       vhost_poll_queue(&node->vq->poll);
> > +                     mutex_unlock(&node->vq->mutex);
> > +
> >                       list_del(&node->node);
> >                       kfree(node);
> >               }
> > @@ -985,7 +977,6 @@ static int vhost_process_iotlb_msg(struct vhost_dev *dev,
> >       int ret = 0;
> >
> >       mutex_lock(&dev->mutex);
> > -     vhost_dev_lock_vqs(dev);
> >       switch (msg->type) {
> >       case VHOST_IOTLB_UPDATE:
> >               if (!dev->iotlb) {
> > @@ -1019,7 +1010,6 @@ static int vhost_process_iotlb_msg(struct vhost_dev *dev,
> >               break;
> >       }
> >
> > -     vhost_dev_unlock_vqs(dev);
> >       mutex_unlock(&dev->mutex);
> >
> >       return ret;
>
> I do prefer the finer-grained locking but I remember we
> discussed something like this in the past and Jason saw issues
> with such a locking.
This change is suggested by Jason. Should I send new version because
the patch 3 is changed.

> Jason?
>
> > --
> > 1.8.3.1