Re: [PATCH tip/core/rcu 43/48] vhost: add __rcu annotations

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, May 04, 2010 at 01:19:53PM -0700, Paul E. McKenney wrote:
> From: Arnd Bergmann <arnd@relay.de.ibm.com>
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> ---
>  drivers/vhost/net.c   |    6 +++---
>  drivers/vhost/vhost.c |   12 ++++++------
>  drivers/vhost/vhost.h |    4 ++--
>  3 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 9777583..36e8dec 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -364,7 +364,7 @@ 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 = rcu_dereference(vq->private_data);

This should be rcu_dereference_const as well: it is called
with vq mutex held.

>  	if (!sock)
>  		return;
>  	if (vq == n->vqs + VHOST_NET_VQ_TX) {
> @@ -380,7 +380,7 @@ 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_const(vq->private_data);
>  	vhost_net_disable_vq(n, vq);
>  	rcu_assign_pointer(vq->private_data, NULL);
>  	mutex_unlock(&vq->mutex);
> @@ -518,7 +518,7 @@ 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_const(vq->private_data);
>  	if (sock == oldsock)
>  		goto done;
>  
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index e69d238..fc9bde2 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_assign_pointer(dev->memory, memory);

This is called when there can be no active readers, so the smp_wmb
inside rcu_assign_pointer isn't really needed.
Use RCU_INIT_POINTER or something like this instead?

>  	return 0;
>  }
>  
> @@ -212,8 +212,8 @@ 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_const(dev->memory));
> +	rcu_assign_pointer(dev->memory, NULL);

Same here.

>  	if (dev->mm)
>  		mmput(dev->mm);
>  	dev->mm = NULL;
> @@ -294,14 +294,14 @@ 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_const(dev->memory), 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(vq->dev->memory),

rcu_dereference_const. This is called under vq mutex and the comment
above it says as much.

>  			    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 +342,7 @@ 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_const(d->memory);
>  	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