Re: [PATCH v3 10/10] lightnvm: track inflight target creations

["Matias Bjørling" <mb@lightnvm.io>]

On 3/27/19 1:39 PM, Igor Konopko wrote:
> This patch adds a counter, which is responsible for tracking inflight
> target creations.
> 
> When creation process is still in progress, target is not yet on
> targets list. This causes a chance for removing whole lightnvm
> subsystem by calling nvm_unregister() in the meantime and finally by
> causing kernel panic inside target init function.
> 
> With this patch we are able to track such a scenarios and wait with
> completing nvm_unregister() and freeing memory until target creation
> will be completed.
> 
> Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
> ---
>   drivers/lightnvm/core.c  | 19 ++++++++++++++++++-
>   include/linux/lightnvm.h |  2 ++
>   2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/lightnvm/core.c b/drivers/lightnvm/core.c
> index e2abe88..62ed662 100644
> --- a/drivers/lightnvm/core.c
> +++ b/drivers/lightnvm/core.c
> @@ -1083,6 +1083,7 @@ static int nvm_core_init(struct nvm_dev *dev)
>   	INIT_LIST_HEAD(&dev->targets);
>   	mutex_init(&dev->mlock);
>   	spin_lock_init(&dev->lock);
> +	dev->create_inflight = 0;
>   
>   	ret = nvm_register_map(dev);
>   	if (ret)
> @@ -1180,6 +1181,11 @@ void nvm_unregister(struct nvm_dev *dev)
>   	struct nvm_target *t, *tmp;
>   
>   	mutex_lock(&dev->mlock);
> +	while (dev->create_inflight > 0) {
> +		mutex_unlock(&dev->mlock);
> +		io_schedule();
> +		mutex_lock(&dev->mlock);
> +	}
>   	list_for_each_entry_safe(t, tmp, &dev->targets, list) {
>   		if (t->dev->parent != dev)
>   			continue;
> @@ -1198,6 +1204,7 @@ EXPORT_SYMBOL(nvm_unregister);
>   static int __nvm_configure_create(struct nvm_ioctl_create *create)
>   {
>   	struct nvm_dev *dev;
> +	int ret;
>   
>   	down_write(&nvm_lock);
>   	dev = nvm_find_nvm_dev(create->dev);
> @@ -1208,7 +1215,17 @@ static int __nvm_configure_create(struct nvm_ioctl_create *create)
>   		return -EINVAL;
>   	}
>   
> -	return nvm_create_tgt(dev, create);
> +	mutex_lock(&dev->mlock);
> +	dev->create_inflight++;
> +	mutex_unlock(&dev->mlock);
> +
> +	ret = nvm_create_tgt(dev, create);
> +
> +	mutex_lock(&dev->mlock);
> +	dev->create_inflight--;
> +	mutex_unlock(&dev->mlock);
> +
> +	return ret;
>   }
>   
>   static long nvm_ioctl_info(struct file *file, void __user *arg)
> diff --git a/include/linux/lightnvm.h b/include/linux/lightnvm.h
> index d3b0270..e462d1d 100644
> --- a/include/linux/lightnvm.h
> +++ b/include/linux/lightnvm.h
> @@ -428,6 +428,8 @@ struct nvm_dev {
>   	char name[DISK_NAME_LEN];
>   	void *private_data;
>   
> +	int create_inflight;
> +
>   	void *rmap;
>   
>   	struct mutex mlock;
> 

Hi Igor,

I think this may be better implemented with kref. Such that target 
creator can take a reference upon target initialize and release it again 
afterwards. Then the one turning of the lights can get to run the final 
cleanup routine.

-Matias