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

Pranay Srivastava
2016-06-25T18:01:16Z

Hi

On Fri, Jun 24, 2016 at 3:39 PM, Pranay Kr. Srivastava
<pranjas@gmail.com> 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.
>
> 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)
> --
> 1.9.1
>

This is supposed to be v3 3/3. Perhaps I gave an incorrect message id
while sending
Should I resend the series afresh [Markus?].

--
---P.K.S