Re: [PATCH 3/3]nbd: make nbd device wait for its users

[Markus Pargmann <mpa@pengutronix.de>]

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Hi,

On Friday 24 June 2016 13:09:36 Pranay Kr. Srivastava wrote:
> When a timeout occurs or a recv fails, then
> instead of abruplty killing nbd block device
> wait for it's users to finish.
> 
> This is more required when filesystem(s) like
> ext2 or ext3 don't expect their buffer heads to
> disappear while the filesystem is mounted.
> 
> Each open of a nbd device is refcounted, while
> the userland program [nbd-client] doing the
> NBD_DO_IT ioctl would now wait for any other users
> of this device before invalidating the nbd device.
> 
> A timedout or a disconnected device, if in use, can't
> be used until it has been resetted. The resetting happens
> when all tasks having this bdev open closes this bdev.

Sorry, but this patch is unreadable. You are changing so many unrelated
whitespaces, lines, comments (that you introduced yourself in a previous
patch) and unrelated code. Please keep only the things that are
necessary for this single patch. Everything else can go into different
patches. Also it would be good to run checkpatch sometimes.

Also using your own atomic implementation instead of kref would be good
perhaps. Although I thought kref would work at the beginning but it
seems not to.

Best Regards,

Markus

> 
> Signed-off-by: Pranay Kr. Srivastava <pranjas@gmail.com>
> ---
>  drivers/block/nbd.c | 124 ++++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 96 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 9223b09..0587bbd 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -70,10 +70,13 @@ struct nbd_device {
>  #if IS_ENABLED(CONFIG_DEBUG_FS)
>  	struct dentry *dbg_dir;
>  #endif
> +
>  	/*
> -	*This is specifically for calling sock_shutdown, for now.
> -	*/
> +	 *This is specifically for calling sock_shutdown, for now.
> +	 */
>  	struct work_struct ws_shutdown;
> +	struct kref users;
> +	struct completion user_completion;
>  };
>  
>  #if IS_ENABLED(CONFIG_DEBUG_FS)
> @@ -104,6 +107,8 @@ static DEFINE_SPINLOCK(nbd_lock);
>   * Shutdown function for nbd_dev work struct.
>   */
>  static void nbd_ws_func_shutdown(struct work_struct *);
> +static void nbd_kref_release(struct kref *);
> +static int nbd_size_clear(struct nbd_device *, struct block_device *);
>  
>  static inline struct device *nbd_to_dev(struct nbd_device *nbd)
>  {
> @@ -129,7 +134,7 @@ static const char *nbdcmd_to_ascii(int cmd)
>  
>  static int nbd_size_clear(struct nbd_device *nbd, struct block_device *bdev)
>  {
> -	bdev->bd_inode->i_size = 0;
> +	i_size_write(bdev->bd_inode, 0);
>  	set_capacity(nbd->disk, 0);
>  	kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
>  
> @@ -141,7 +146,7 @@ static void nbd_size_update(struct nbd_device *nbd, struct block_device *bdev)
>  	if (!nbd_is_connected(nbd))
>  		return;
>  
> -	bdev->bd_inode->i_size = nbd->bytesize;
> +	i_size_write(bdev->bd_inode, nbd->bytesize);
>  	set_capacity(nbd->disk, nbd->bytesize >> 9);
>  	kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
>  }
> @@ -150,11 +155,9 @@ static int nbd_size_set(struct nbd_device *nbd, struct block_device *bdev,
>  			int blocksize, int nr_blocks)
>  {
>  	int ret;
> -
>  	ret = set_blocksize(bdev, blocksize);
>  	if (ret)
>  		return ret;
> -
>  	nbd->blksize = blocksize;
>  	nbd->bytesize = (loff_t)blocksize * (loff_t)nr_blocks;
>  
> @@ -202,14 +205,19 @@ static void nbd_xmit_timeout(unsigned long arg)
>  {
>  	struct nbd_device *nbd = (struct nbd_device *)arg;
>  
> +	if (nbd->timedout)
> +		return;
> +
>  	if (list_empty(&nbd->queue_head))
>  		return;
> +
>  	nbd->timedout = true;
> -	schedule_work(&nbd->ws_shutdown);
> +
>  	/*
>  	 * Make sure sender thread sees nbd->timedout.
>  	 */
>  	smp_wmb();
> +	schedule_work(&nbd->ws_shutdown);
>  	wake_up(&nbd->waiting_wq);
>  	dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
>  }
> @@ -476,8 +484,6 @@ static int nbd_thread_recv(struct nbd_device *nbd, struct block_device *bdev)
>  		nbd_end_request(nbd, req);
>  	}
>  
> -	nbd_size_clear(nbd, bdev);
> -
>  	device_remove_file(disk_to_dev(nbd->disk), &dev_attr_pid);
>  
>  	nbd->task_recv = NULL;
> @@ -580,8 +586,8 @@ static int nbd_thread_send(void *data)
>  	while (!kthread_should_stop() || !list_empty(&nbd->waiting_queue)) {
>  		/* wait for something to do */
>  		wait_event_interruptible(nbd->waiting_wq,
> -				kthread_should_stop() ||
> -				!list_empty(&nbd->waiting_queue));
> +					 kthread_should_stop() ||
> +					 !list_empty(&nbd->waiting_queue));
>  
>  		/* extract request */
>  		if (list_empty(&nbd->waiting_queue))
> @@ -589,11 +595,11 @@ static int nbd_thread_send(void *data)
>  
>  		spin_lock_irq(&nbd->queue_lock);
>  		req = list_entry(nbd->waiting_queue.next, struct request,
> -				queuelist);
> +				 queuelist);
>  		list_del_init(&req->queuelist);
>  		spin_unlock_irq(&nbd->queue_lock);
>  
> -		nbd_handle_req(nbd, req);
> +		/* handle request */
>  		if (nbd->timedout) {
>  			req->errors++;
>  			nbd_end_request(nbd, req);
> @@ -654,12 +660,13 @@ static int nbd_set_socket(struct nbd_device *nbd, struct socket *sock)
>  	int ret = 0;
>  
>  	spin_lock(&nbd->sock_lock);
> -	if (nbd->sock)
> +
> +	if (nbd->sock || nbd->timedout)
>  		ret = -EBUSY;
>  	else
>  		nbd->sock = sock;
> -	spin_unlock(&nbd->sock_lock);
>  
> +	spin_unlock(&nbd->sock_lock);
>  	return ret;
>  }
>  
> @@ -674,6 +681,7 @@ static void nbd_reset(struct nbd_device *nbd)
>  	nbd->flags = 0;
>  	nbd->xmit_timeout = 0;
>  	INIT_WORK(&nbd->ws_shutdown, nbd_ws_func_shutdown);
> +	init_completion(&nbd->user_completion);
>  	queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
>  	del_timer_sync(&nbd->timeout_timer);
>  }
> @@ -708,6 +716,9 @@ static void nbd_dev_dbg_close(struct nbd_device *nbd);
>  static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  		       unsigned int cmd, unsigned long arg)
>  {
> +	if (nbd->timedout || nbd->disconnect)
> +		return -EBUSY;
> +
>  	switch (cmd) {
>  	case NBD_DISCONNECT: {
>  		struct request sreq;
> @@ -737,7 +748,6 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  		nbd_clear_que(nbd);
>  		BUG_ON(!list_empty(&nbd->queue_head));
>  		BUG_ON(!list_empty(&nbd->waiting_queue));
> -		kill_bdev(bdev);
>  		return 0;
>  
>  	case NBD_SET_SOCK: {
> @@ -756,7 +766,6 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  
>  	case NBD_SET_BLKSIZE: {
>  		loff_t bsize = div_s64(nbd->bytesize, arg);
> -
>  		return nbd_size_set(nbd, bdev, arg, bsize);
>  	}
>  
> @@ -808,22 +817,29 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  		error = nbd_thread_recv(nbd, bdev);
>  		nbd_dev_dbg_close(nbd);
>  		kthread_stop(thread);
> -		sock_shutdown(nbd);
>  
> -		mutex_lock(&nbd->tx_lock);
> -		nbd->task_recv = NULL;
> -
> -		nbd_clear_que(nbd);
> -		kill_bdev(bdev);
> -		nbd_bdev_reset(bdev);
> +		sock_shutdown(nbd);
>  
>  		if (nbd->disconnect) /* user requested, ignore socket errors */
>  			error = 0;
>  		if (nbd->timedout)
>  			error = -ETIMEDOUT;
>  
> -		nbd_reset(nbd);
> +		mutex_lock(&nbd->tx_lock);
> +		nbd_clear_que(nbd);
> +		nbd->disconnect = true; /* To kill bdev*/
> +		mutex_unlock(&nbd->tx_lock);
> +		cancel_work_sync(&nbd->ws_shutdown);
> +		kref_put(&nbd->users, nbd_kref_release);
> +		wait_for_completion(&nbd->user_completion);
>  
> +		mutex_lock(&bdev->bd_mutex);
> +		if (!kref_get_unless_zero(&nbd->users))
> +			kref_init(&nbd->users);
> +		mutex_unlock(&bdev->bd_mutex);
> +
> +		mutex_lock(&nbd->tx_lock);
> +		nbd_reset(nbd);
>  		return error;
>  	}
>  
> @@ -861,19 +877,71 @@ static int nbd_ioctl(struct block_device *bdev, fmode_t mode,
>  
>  	return error;
>  }
> +static void nbd_kref_release(struct kref *kref_users)
> +{
> +	struct nbd_device *nbd = container_of(kref_users, struct nbd_device,
> +			users);
> +	schedule_work(&nbd->ws_shutdown);
> +}
> +
> +static int nbd_open(struct block_device *bdev, fmode_t mode)
> +{
> +	struct nbd_device *nbd_dev = bdev->bd_disk->private_data;
> +
> +	if (!kref_get_unless_zero(&nbd_dev->users))
> +		kref_init(&nbd_dev->users);
> +
> +	pr_debug("Opening nbd_dev %s. Active users = %u\n",
> +			bdev->bd_disk->disk_name,
> +			atomic_read(&nbd_dev->users.refcount)
> +		);
> +	return 0;
> +}
> +
> +static void nbd_release(struct gendisk *disk, fmode_t mode)
> +{
> +	struct nbd_device *nbd_dev = disk->private_data;
> +
> +	kref_put(&nbd_dev->users,  nbd_kref_release);
> +
> +	pr_debug("Closing nbd_dev %s. Active users = %u\n",
> +			disk->disk_name,
> +			atomic_read(&nbd_dev->users.refcount)
> +		);
> +}
>  
>  static const struct block_device_operations nbd_fops = {
>  	.owner =	THIS_MODULE,
>  	.ioctl =	nbd_ioctl,
>  	.compat_ioctl =	nbd_ioctl,
> +	.open =		nbd_open,
> +	.release =	nbd_release
>  };
>  
> +
>  static void nbd_ws_func_shutdown(struct work_struct *ws_nbd)
>  {
>  	struct nbd_device *nbd_dev = container_of(ws_nbd, struct nbd_device,
> -			ws_shutdown);
> -
> -	sock_shutdown(nbd_dev);
> +							ws_shutdown);
> +	struct block_device *bdev = bdget(part_devt(
> +						dev_to_part(nbd_to_dev(nbd_dev))
> +						)
> +					);
> +	BUG_ON(!bdev);
> +	if (nbd_dev->timedout)
> +		sock_shutdown(nbd_dev);
> +
> +	if (nbd_dev->disconnect) {
> +		mutex_lock(&nbd_dev->tx_lock);
> +		nbd_dev->task_recv = NULL;
> +		nbd_clear_que(nbd_dev);
> +		kill_bdev(bdev);
> +		nbd_bdev_reset(bdev);
> +		mutex_unlock(&nbd_dev->tx_lock);
> +		nbd_size_clear(nbd_dev, bdev);
> +		complete(&nbd_dev->user_completion);
> +	}
> +	bdput(bdev);
>  }
>  
>  #if IS_ENABLED(CONFIG_DEBUG_FS)
> 

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