Re: [PATCH RFC tip/core/rcu 23/23] vhost: add __rcu annotations

[Paul E. McKenney]

On Thu, May 13, 2010 at 12:48:47AM +0300, Michael S. Tsirkin wrote:
> On Wed, May 12, 2010 at 02:33:42PM -0700, Paul E. McKenney wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxxxxxxxxxx>
> > 
> > Also add rcu_dreference_protected() for code paths where locks are held.
> > 
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> 
> Maybe long lines can be fixed? Otherwise looks ok.

Done.  I introduced locals to make it fit.

One other thing...  We need some API that says "we are running in the
context of a work queue."  Otherwise, we will get false positives when
called in a work queue without locks held.

Any thoughts?  One approach would be to create a separate lockdep class
for vhost workqueue state, similar to the approach used in instrument
rcu_read_lock() and friends.

							Thanx, Paul

> > ---
> >  drivers/vhost/net.c   |   11 ++++++++---
> >  drivers/vhost/vhost.c |   14 ++++++++------
> >  drivers/vhost/vhost.h |    4 ++--
> >  3 files changed, 18 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index 9777583..945c5cb 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -364,7 +364,10 @@ static void vhost_net_disable_vq(struct vhost_net *n,
> >  static void vhost_net_enable_vq(struct vhost_net *n,
> >  				struct vhost_virtqueue *vq)
> >  {
> > -	struct socket *sock = vq->private_data;
> > +	struct socket *sock;
> > +
> > +	sock = rcu_dereference_protected(vq->private_data,
> > +					 lockdep_is_held(&vq->mutex));
> >  	if (!sock)
> >  		return;
> >  	if (vq == n->vqs + VHOST_NET_VQ_TX) {
> > @@ -380,7 +383,8 @@ static struct socket *vhost_net_stop_vq(struct vhost_net *n,
> >  	struct socket *sock;
> >  
> >  	mutex_lock(&vq->mutex);
> > -	sock = vq->private_data;
> > +	sock = rcu_dereference_protected(vq->private_data,
> > +					 lockdep_is_held(&vq->mutex));
> >  	vhost_net_disable_vq(n, vq);
> >  	rcu_assign_pointer(vq->private_data, NULL);
> >  	mutex_unlock(&vq->mutex);
> > @@ -518,7 +522,8 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
> >  	}
> >  
> >  	/* start polling new socket */
> > -	oldsock = vq->private_data;
> > +	oldsock = rcu_dereference_protected(vq->private_data,
> > +					    lockdep_is_held(&vq->mutex));
> >  	if (sock == oldsock)
> >  		goto done;
> >  
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index e69d238..fc0c077 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -180,7 +180,7 @@ long vhost_dev_reset_owner(struct vhost_dev *dev)
> >  	vhost_dev_cleanup(dev);
> >  
> >  	memory->nregions = 0;
> > -	dev->memory = memory;
> > +	RCU_INIT_POINTER(dev->memory, memory);
> >  	return 0;
> >  }
> >  
> > @@ -212,8 +212,9 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> >  		fput(dev->log_file);
> >  	dev->log_file = NULL;
> >  	/* No one will access memory at this point */
> > -	kfree(dev->memory);
> > -	dev->memory = NULL;
> > +	kfree(rcu_dereference_protected(dev->memory,
> > +					lockdep_is_held(&dev->mutex)));
> > +	RCU_INIT_POINTER(dev->memory, NULL);
> >  	if (dev->mm)
> >  		mmput(dev->mm);
> >  	dev->mm = NULL;
> > @@ -294,14 +295,14 @@ static int vq_access_ok(unsigned int num,
> >  /* Caller should have device mutex but not vq mutex */
> >  int vhost_log_access_ok(struct vhost_dev *dev)
> >  {
> > -	return memory_access_ok(dev, dev->memory, 1);
> > +	return memory_access_ok(dev, rcu_dereference_protected(dev->memory, lockdep_is_held(&dev->mutex)), 1);
> >  }
> >  
> >  /* Verify access for write logging. */
> >  /* Caller should have vq mutex and device mutex */
> >  static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base)
> >  {
> > -	return vq_memory_access_ok(log_base, vq->dev->memory,
> > +	return vq_memory_access_ok(log_base, rcu_dereference_protected(vq->dev->memory, lockdep_is_held(&dev->mutex)),
> >  			    vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
> >  		(!vq->log_used || log_access_ok(log_base, vq->log_addr,
> >  					sizeof *vq->used +
> > @@ -342,7 +343,8 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
> >  
> >  	if (!memory_access_ok(d, newmem, vhost_has_feature(d, VHOST_F_LOG_ALL)))
> >  		return -EFAULT;
> > -	oldmem = d->memory;
> > +	oldmem = rcu_dereference_protected(d->memory,
> > +					   lockdep_is_held(&d->mutex));
> >  	rcu_assign_pointer(d->memory, newmem);
> >  	synchronize_rcu();
> >  	kfree(oldmem);
> > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > index 44591ba..240396c 100644
> > --- a/drivers/vhost/vhost.h
> > +++ b/drivers/vhost/vhost.h
> > @@ -92,7 +92,7 @@ struct vhost_virtqueue {
> >  	 * work item execution acts instead of rcu_read_lock() and the end of
> >  	 * work item execution acts instead of rcu_read_lock().
> >  	 * Writers use virtqueue mutex. */
> > -	void *private_data;
> > +	void __rcu *private_data;
> >  	/* Log write descriptors */
> >  	void __user *log_base;
> >  	struct vhost_log log[VHOST_NET_MAX_SG];
> > @@ -102,7 +102,7 @@ struct vhost_dev {
> >  	/* Readers use RCU to access memory table pointer
> >  	 * log base pointer and features.
> >  	 * Writers use mutex below.*/
> > -	struct vhost_memory *memory;
> > +	struct vhost_memory __rcu *memory;
> >  	struct mm_struct *mm;
> >  	struct mutex mutex;
> >  	unsigned acked_features;
> > -- 
> > 1.7.0.6
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