From: Markus Pargmann <mpa@pengutronix.de>
To: "Pranay Kr. Srivastava" <pranjas@gmail.com>
Cc: nbd-general@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] make nbd device wait for its users.
Date: Mon, 30 May 2016 12:44:50 +0200 [thread overview]
Message-ID: <16646016.gAJCF3ZoFN@adelgunde> (raw)
In-Reply-To: <1464089188-6155-4-git-send-email-pranjas@gmail.com>
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Hi,
sorry I couldn't fit the review into last week.
On Tuesday 24 May 2016 14:26:27 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.
>
> Use a kref for users using this. The device will
> be released for kref count of 2, not less or more.
>
> Signed-off-by: Pranay Kr. Srivastava <pranjas@gmail.com>
> ---
> drivers/block/nbd.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 51 insertions(+)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index af86c9b..59db890 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -71,6 +71,8 @@ struct nbd_device {
> struct dentry *dbg_dir;
> #endif
> struct work_struct ws_nbd;
> + struct kref users;
> + struct completion user_completion;
> };
>
> #if IS_ENABLED(CONFIG_DEBUG_FS)
> @@ -674,6 +676,7 @@ static void nbd_reset(struct nbd_device *nbd)
> nbd->flags = 0;
> nbd->xmit_timeout = 0;
> INIT_WORK(&nbd->ws_nbd, nbd_work_func);
> + init_completion(&nbd->user_completion);
> queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
> del_timer_sync(&nbd->timeout_timer);
> }
> @@ -807,6 +810,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
> kthread_stop(thread);
>
> sock_shutdown(nbd);
> + wait_for_completion(&nbd->user_completion);
> mutex_lock(&nbd->tx_lock);
> nbd_clear_que(nbd);
> kill_bdev(bdev);
> @@ -858,12 +862,58 @@ 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);
> + pr_debug("Releasing kref [%s]\n", __FUNCTION__);
> + complete(&nbd->user_completion);
> +
> +}
> +
> +static int nbd_open(struct block_device *bdev, fmode_t mode)
> +{
> + struct nbd_device *nbd_dev = bdev->bd_disk->private_data;
> +
> + kref_get(&nbd_dev->users);
> + pr_debug("Opening nbd_dev %s. Active users = %u\n",
> + bdev->bd_disk->disk_name,
> + atomic_read(&nbd_dev->users.refcount) - 1);
> + return 0;
> +}
> +
> +static void nbd_release(struct gendisk *disk, fmode_t mode)
> +{
> + struct nbd_device *nbd_dev = disk->private_data;
> + /*
> + *kref_init initializes ref count to 1, so we
> + *we check for refcount to be 2 for a final put.
> + *
> + *kref needs to be re-initialized just here as the
> + *other process holding it must see the ref count as 2.
> + */
> + kref_put(&nbd_dev->users, nbd_kref_release);
> +
> + if (atomic_read(&nbd_dev->users.refcount) == 2) {
> + kref_sub(&nbd_dev->users, 2, nbd_kref_release);
> + kref_init(&nbd_dev->users);
> + kref_get(&nbd_dev->users);
Reading the refcount directly seems not to be as it supposed to be.
Why don't you put a kref_init() and kref_put() call into NBD_DO_IT? This
way you don't have to work around the property that kref_init() starts
with a refcount of 1 but you can use it.
For example:
NBD_DO_IT:
kref_init()
...
kref_put()
nbd_thread_recv() and nbd_thread_send():
kref_get()
...
kref_put()
In nbd_open() you could use kref_get_unless_zero() to avoid
opening a not connected device.
nbd_release() would then be a very simple kref_put() without
checking for 2 and so on.
Also there are some checkpatch issues with this patch.
Best Regards,
Markus
> + }
> +
> + pr_debug("Closing nbd_dev %s. Active users = %u\n",
> + disk->disk_name,
> + atomic_read(&nbd_dev->users.refcount) - 1);
> +}
> +
> 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_work_func(struct work_struct *ws_nbd)
> {
> struct nbd_device *nbd_dev = container_of(ws_nbd, struct nbd_device,
> @@ -1098,6 +1148,7 @@ static int __init nbd_init(void)
> disk->first_minor = i << part_shift;
> disk->fops = &nbd_fops;
> disk->private_data = &nbd_dev[i];
> + kref_init(&nbd_dev[i].users);
> sprintf(disk->disk_name, "nbd%d", i);
> nbd_reset(&nbd_dev[i]);
> add_disk(disk);
>
--
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next prev parent reply other threads:[~2016-05-30 10:44 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-24 11:26 [PATCH 0/4]nbd: fixes for nbd Pranay Kr. Srivastava
2016-05-24 11:26 ` [PATCH 1/4] fix might_sleep warning on socket shutdown Pranay Kr. Srivastava
2016-05-30 12:06 ` Markus Pargmann
2016-05-24 11:26 ` [PATCH 2/4] fix various coding standard warnings Pranay Kr. Srivastava
2016-05-24 11:26 ` [PATCH 3/4] make nbd device wait for its users Pranay Kr. Srivastava
2016-05-30 10:44 ` Markus Pargmann [this message]
2016-05-24 11:26 ` [PATCH 4/4] use device_attr macros for sysfs attribute Pranay Kr. Srivastava
2016-05-30 3:35 ` [PATCH 0/4]nbd: fixes for nbd Pranay Srivastava
2016-05-30 12:27 ` Markus Pargmann
2016-06-02 10:24 ` [PATCH v2 0/5] nbd: " Pranay Kr. Srivastava
2016-06-02 10:24 ` [PATCH v2 1/5] nbd: fix might_sleep warning on socket shutdown Pranay Kr. Srivastava
2016-06-09 10:03 ` Pranay Srivastava
2016-06-14 5:13 ` Pranay Srivastava
2016-06-14 8:52 ` Markus Pargmann
2016-06-14 9:50 ` Pranay Srivastava
2016-06-24 10:09 ` [PATCH v3 0/3] nbd: resolve bugs and limitations Pranay Kr. Srivastava
2016-06-24 10:09 ` [PATCH v3 1/3]nbd: fix might_sleep warning on socket shutdown Pranay Kr. Srivastava
2016-06-28 5:42 ` Pranay Srivastava
2016-06-29 7:18 ` Markus Pargmann
2016-06-24 10:09 ` [PATCH v3 2/3]nbd: cleanup nbd_set_socket Pranay Kr. Srivastava
2016-06-24 10:09 ` [PATCH 3/3]nbd: make nbd device wait for its users Pranay Kr. Srivastava
2016-06-24 13:42 ` [Nbd] " Eric Blake
2016-06-25 17:56 ` Pranay Srivastava
2016-06-25 18:01 ` Pranay Srivastava
2016-06-29 7:06 ` Markus Pargmann
2016-06-29 7:15 ` Pranay Srivastava
2016-06-02 10:24 ` [PATCH v2 2/5]nbd: cleanup nbd_set_socket Pranay Kr. Srivastava
2016-06-02 10:24 ` [PATCH v2 3/5]nbd: fix various coding standard warnings Pranay Kr. Srivastava
2016-06-02 10:25 ` [PATCH v2 4/5]nbd: make nbd device wait for its users Pranay Kr. Srivastava
2016-06-14 8:59 ` Markus Pargmann
2016-06-14 9:33 ` Pranay Srivastava
2016-06-15 6:30 ` Markus Pargmann
2016-06-15 7:00 ` [Nbd] " Wouter Verhelst
2016-06-15 9:18 ` Pranay Srivastava
2016-06-15 9:17 ` Pranay Srivastava
2016-06-24 9:29 ` [PATCH 1/2] nbd: " Markus Pargmann
2016-06-24 9:29 ` [PATCH 2/2] nbd: Disallow ioctls on disconnected block device Markus Pargmann
2016-07-16 7:42 ` Pranay Srivastava
2016-07-16 9:32 ` [Nbd] " Alex Bligh
2016-07-16 10:08 ` Pranay Srivastava
2016-07-16 11:26 ` Wouter Verhelst
2016-07-16 13:31 ` Pranay Srivastava
2016-06-24 9:39 ` [PATCH 1/2] nbd: make nbd device wait for its users Pranay Srivastava
2016-06-24 13:40 ` [Nbd] " Eric Blake
2016-06-25 17:52 ` Pranay Srivastava
2016-06-29 6:57 ` Markus Pargmann
2016-06-02 10:25 ` [PATCH v2 5/5]nbd: use device_attr macros for sysfs attribute Pranay Kr. Srivastava
[not found] ` <CA+aCy1E0S4ofa04xcO9qxQmuipaF5wdnrv3ubSvETn-rBYYisA@mail.gmail.com>
2016-06-06 11:07 ` [PATCH 0/4]nbd: fixes for nbd Pranay Srivastava
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