Re: [PATCH] gntdev: switch back to rwlocks

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 07/09/2010 07:32 AM, Stefano Stabellini wrote:
> Hi Jeremy,
> this patch switches back from spinlocks to rwlocks in gntdev, solving
> the locking issue that was preventing stubdoms from working.
> In particular the problem is that gntdev_mmap calls apply_to_page_range
> after acquiring the spinlock. apply_to_page_range causes the mmu
> notifiers to be called, so mn_invl_range_start will be called that will
> try to acquire again the same spinlock.
>   

I think the problem is that apply_to_page_range is calling the mmu
notifiers at all.  It seems to be plain bogus; it should be up to the
callers of apply_to_page_range to call the mmu notifiers if necessary.

Does removing those calls fix the problem?

Thanks,
    J

> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>
> ---
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index a33e443..0a9a68c 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -51,7 +51,7 @@ struct gntdev_priv {
>  	struct list_head maps;
>  	uint32_t used;
>  	uint32_t limit;
> -	spinlock_t lock;
> +	rwlock_t rwlock;
>  	struct mm_struct *mm;
>  	struct mmu_notifier mn;
>  };
> @@ -289,7 +289,7 @@ static void mn_invl_range_start(struct mmu_notifier *mn,
>  	unsigned long mstart, mend;
>  	int err;
>  
> -	spin_lock(&priv->lock);
> +	read_lock(&priv->rwlock);
>  	list_for_each_entry(map, &priv->maps, next) {
>  		if (!map->vma)
>  			continue;
> @@ -311,7 +311,7 @@ static void mn_invl_range_start(struct mmu_notifier *mn,
>  					(mend - mstart) >> PAGE_SHIFT);
>  		WARN_ON(err);
>  	}
> -	spin_unlock(&priv->lock);
> +	read_unlock(&priv->rwlock);
>  }
>  
>  static void mn_invl_page(struct mmu_notifier *mn,
> @@ -328,7 +328,7 @@ static void mn_release(struct mmu_notifier *mn,
>  	struct grant_map *map;
>  	int err;
>  
> -	spin_lock(&priv->lock);
> +	read_lock(&priv->rwlock);
>  	list_for_each_entry(map, &priv->maps, next) {
>  		if (!map->vma)
>  			continue;
> @@ -339,7 +339,7 @@ static void mn_release(struct mmu_notifier *mn,
>  		err = unmap_grant_pages(map, 0, map->count);
>  		WARN_ON(err);
>  	}
> -	spin_unlock(&priv->lock);
> +	read_unlock(&priv->rwlock);
>  }
>  
>  struct mmu_notifier_ops gntdev_mmu_ops = {
> @@ -359,7 +359,7 @@ static int gntdev_open(struct inode *inode, struct file *flip)
>  		return -ENOMEM;
>  
>  	INIT_LIST_HEAD(&priv->maps);
> -	spin_lock_init(&priv->lock);
> +	priv->rwlock = RW_LOCK_UNLOCKED;
>  	priv->limit = limit;
>  
>  	priv->mm = get_task_mm(current);
> @@ -387,7 +387,7 @@ static int gntdev_release(struct inode *inode, struct file *flip)
>  	if (debug)
>  		printk("%s: priv %p\n", __FUNCTION__, priv);
>  
> -	spin_lock(&priv->lock);
> +	write_lock(&priv->rwlock);
>  	while (!list_empty(&priv->maps)) {
>  		map = list_entry(priv->maps.next, struct grant_map, next);
>  		err = gntdev_del_map(map);
> @@ -395,7 +395,7 @@ static int gntdev_release(struct inode *inode, struct file *flip)
>  			gntdev_free_map(map);
>  
>  	}
> -	spin_unlock(&priv->lock);
> +	write_unlock(&priv->rwlock);
>  
>  	mmu_notifier_unregister(&priv->mn, priv->mm);
>  	kfree(priv);
> @@ -429,15 +429,15 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,
>  		return err;
>  	}
>  
> -	spin_lock(&priv->lock);
> +	write_lock(&priv->rwlock);
>  	gntdev_add_map(priv, map);
>  	op.index = map->index << PAGE_SHIFT;
> -	spin_unlock(&priv->lock);
> +	write_unlock(&priv->rwlock);
>  
>  	if (copy_to_user(u, &op, sizeof(op)) != 0) {
> -		spin_lock(&priv->lock);
> +		write_lock(&priv->rwlock);
>  		gntdev_del_map(map);
> -		spin_unlock(&priv->lock);
> +		write_unlock(&priv->rwlock);
>  		gntdev_free_map(map);
>  		return err;
>  	}
> @@ -457,11 +457,11 @@ static long gntdev_ioctl_unmap_grant_ref(struct gntdev_priv *priv,
>  		printk("%s: priv %p, del %d+%d\n", __FUNCTION__, priv,
>  		       (int)op.index, (int)op.count);
>  
> -	spin_lock(&priv->lock);
> +	write_lock(&priv->rwlock);
>  	map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
>  	if (map)
>  		err = gntdev_del_map(map);
> -	spin_unlock(&priv->lock);
> +	write_unlock(&priv->rwlock);
>  	if (!err)
>  		gntdev_free_map(map);
>  	return err;
> @@ -479,16 +479,16 @@ static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
>  		printk("%s: priv %p, offset for vaddr %lx\n", __FUNCTION__, priv,
>  		       (unsigned long)op.vaddr);
>  
> -	spin_lock(&priv->lock);
> +	read_lock(&priv->rwlock);
>  	map = gntdev_find_map_vaddr(priv, op.vaddr);
>  	if (map == NULL ||
>  	    map->vma->vm_start != op.vaddr) {
> -		spin_unlock(&priv->lock);
> +		read_unlock(&priv->rwlock);
>  		return -EINVAL;
>  	}
>  	op.offset = map->index << PAGE_SHIFT;
>  	op.count = map->count;
> -	spin_unlock(&priv->lock);
> +	read_unlock(&priv->rwlock);
>  
>  	if (copy_to_user(u, &op, sizeof(op)) != 0)
>  		return -EFAULT;
> @@ -507,9 +507,9 @@ static long gntdev_ioctl_set_max_grants(struct gntdev_priv *priv,
>  	if (op.count > limit)
>  		return -EINVAL;
>  
> -	spin_lock(&priv->lock);
> +	write_lock(&priv->rwlock);
>  	priv->limit = op.count;
> -	spin_unlock(&priv->lock);
> +	write_unlock(&priv->rwlock);
>  	return 0;
>  }
>  
> @@ -557,7 +557,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>  		printk("%s: map %d+%d at %lx (pgoff %lx)\n", __FUNCTION__,
>  		       index, count, vma->vm_start, vma->vm_pgoff);
>  
> -	spin_lock(&priv->lock);
> +	read_lock(&priv->rwlock);
>  	map = gntdev_find_map_index(priv, index, count);
>  	if (!map)
>  		goto unlock_out;
> @@ -599,7 +599,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>  	map->is_mapped = 1;
>  
>  unlock_out:
> -	spin_unlock(&priv->lock);
> +	read_unlock(&priv->rwlock);
>  	return err;
>  }
>  
>
>