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

Pranay Srivastava
2016-06-29T07:15:06Z

Hi

On Wed, Jun 29, 2016 at 12:36 PM, Markus Pargmann <mpa@pengutronix.de> wrote:
> 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

Yes you are right.

> 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.

I was able to make it work and it turned out to be simpler.
Do you think you can go over this patch again just for the kref part?
Should I resend this patch again?

>
> 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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