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Message-ID: <20160607134010.GB13083@neilslaptop.think-freely.org>
Date: Tue, 7 Jun 2016 09:40:10 -0400
From: Neil Horman <nhorman@...hat.com>
To: David Kershner <david.kershner@...sys.com>
Cc: corbet@....net, tglx@...utronix.de, mingo@...hat.com,
hpa@...or.com, gregkh@...uxfoundation.org,
erik.arfvidson@...sys.com, timothy.sell@...sys.com,
hofrat@...dl.org, dzickus@...hat.com, jes.sorensen@...hat.com,
alexander.curtin@...sys.com, janani.rvchndrn@...il.com,
sudipm.mukherjee@...il.com, prarit@...hat.com,
david.binder@...sys.com, dan.j.williams@...el.com,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
driverdev-devel@...uxdriverproject.org, sparmaintainer@...sys.com
Subject: Re: [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer
instead of workqueue
On Sat, Jun 04, 2016 at 01:27:11PM -0400, David Kershner wrote:
> From: Tim Sell <Timothy.Sell@...sys.com>
>
> A kernel timer is now used as the vehicle to periodically call the
> channel_interrupt function of registered visor drivers, instead of a
> workqueue.
>
> This simplifies a lot of things by making periodic_work.c and
> periodic_work.h no longer necessary. This change also means that the
> channel_interrupt() callbacks registered by visor drivers (via
> visorbus_register_visor_driver()) will now be called in atomic context
> (i.e., canNOT sleep) rather than kernel thread context (CAN sleep).
> Fortunately this did NOT necessitate any change to the existing
> channel_interrupt() callbacks, because none of them ever perform any
> operations that would be invalid in atomic context.
>
> Signed-off-by: Tim Sell <Timothy.Sell@...sys.com>
> Signed-off-by: David Kershner <david.kershner@...sys.com>
> ---
> drivers/staging/unisys/include/visorbus.h | 10 +++--
> drivers/staging/unisys/visorbus/visorbus_main.c | 54 +++++++------------------
> 2 files changed, 21 insertions(+), 43 deletions(-)
>
> diff --git a/drivers/staging/unisys/include/visorbus.h b/drivers/staging/unisys/include/visorbus.h
> index 9baf1ec..9bb88bb 100644
> --- a/drivers/staging/unisys/include/visorbus.h
> +++ b/drivers/staging/unisys/include/visorbus.h
> @@ -34,8 +34,9 @@
> #include <linux/poll.h>
> #include <linux/kernel.h>
> #include <linux/uuid.h>
> +#include <linux/seq_file.h>
> +#include <linux/slab.h>
>
> -#include "periodic_work.h"
> #include "channel.h"
>
> struct visor_driver;
> @@ -126,8 +127,8 @@ struct visor_driver {
> * device: Device struct meant for use by the bus driver
> * only.
> * list_all: Used by the bus driver to enumerate devices.
> - * periodic_work: Device work queue. Private use by bus driver
> - * only.
> + * timer: Timer fired periodically to do interrupt-type
> + * activity.
> * being_removed: Indicates that the device is being removed from
> * the bus. Private bus driver use only.
> * visordriver_callback_lock: Used by the bus driver to lock when handling
> @@ -157,7 +158,8 @@ struct visor_device {
> /* These fields are for private use by the bus driver only. */
> struct device device;
> struct list_head list_all;
> - struct periodic_work *periodic_work;
> + struct timer_list timer;
> + bool timer_active;
> bool being_removed;
> struct semaphore visordriver_callback_lock;
> bool pausing;
> diff --git a/drivers/staging/unisys/visorbus/visorbus_main.c b/drivers/staging/unisys/visorbus/visorbus_main.c
> index ebdd5de..e98e720 100644
> --- a/drivers/staging/unisys/visorbus/visorbus_main.c
> +++ b/drivers/staging/unisys/visorbus/visorbus_main.c
> @@ -19,7 +19,6 @@
> #include "visorbus.h"
> #include "visorbus_private.h"
> #include "version.h"
> -#include "periodic_work.h"
> #include "vbuschannel.h"
> #include "guestlinuxdebug.h"
> #include "vmcallinterface.h"
> @@ -116,7 +115,6 @@ struct bus_type visorbus_type = {
> .bus_groups = visorbus_bus_groups,
> };
>
> -static struct workqueue_struct *periodic_dev_workqueue;
> static long long bus_count; /** number of bus instances */
> /** ever-increasing */
>
> @@ -222,10 +220,6 @@ visorbus_release_device(struct device *xdev)
> {
> struct visor_device *dev = to_visor_device(xdev);
>
> - if (dev->periodic_work) {
> - visor_periodic_work_destroy(dev->periodic_work);
> - dev->periodic_work = NULL;
> - }
> if (dev->visorchannel) {
> visorchannel_destroy(dev->visorchannel);
> dev->visorchannel = NULL;
> @@ -530,35 +524,36 @@ unregister_driver_attributes(struct visor_driver *drv)
> }
>
> static void
> -dev_periodic_work(void *xdev)
> +dev_periodic_work(unsigned long __opaque)
> {
> - struct visor_device *dev = xdev;
> + struct visor_device *dev = (struct visor_device *)__opaque;
> struct visor_driver *drv = to_visor_driver(dev->device.driver);
>
> - down(&dev->visordriver_callback_lock);
> if (drv->channel_interrupt)
> drv->channel_interrupt(dev);
visorinput_channel_interrupt uses down_write (and other channel_interrupt
methods may do the same). While its legal to use semaphores in interrupt
context, you need to convert that/those calls to the trylock variants and handle
a failed lock to avoid blocking when in interrupt context, which moving to a
timer handler puts you in.
> - up(&dev->visordriver_callback_lock);
> - if (!visor_periodic_work_nextperiod(dev->periodic_work))
> - put_device(&dev->device);
> + mod_timer(&dev->timer, jiffies + POLLJIFFIES_NORMALCHANNEL);
> }
>
> static void
> dev_start_periodic_work(struct visor_device *dev)
> {
> - if (dev->being_removed)
> + if (dev->being_removed || dev->timer_active)
> return;
> /* now up by at least 2 */
> get_device(&dev->device);
> - if (!visor_periodic_work_start(dev->periodic_work))
> - put_device(&dev->device);
> + dev->timer.expires = jiffies + POLLJIFFIES_NORMALCHANNEL;
> + add_timer(&dev->timer);
> + dev->timer_active = true;
> }
>
> static void
> dev_stop_periodic_work(struct visor_device *dev)
> {
> - if (visor_periodic_work_stop(dev->periodic_work))
> - put_device(&dev->device);
> + if (!dev->timer_active)
> + return;
> + del_timer_sync(&dev->timer);
> + dev->timer_active = false;
> + put_device(&dev->device);
> }
>
> /** This is called automatically upon adding a visor_device (device_add), or
> @@ -776,17 +771,9 @@ create_visor_device(struct visor_device *dev)
> dev->device.release = visorbus_release_device;
> /* keep a reference just for us (now 2) */
> get_device(&dev->device);
> - dev->periodic_work =
> - visor_periodic_work_create(POLLJIFFIES_NORMALCHANNEL,
> - periodic_dev_workqueue,
> - dev_periodic_work,
> - dev, dev_name(&dev->device));
> - if (!dev->periodic_work) {
> - POSTCODE_LINUX_3(DEVICE_CREATE_FAILURE_PC, chipset_dev_no,
> - DIAG_SEVERITY_ERR);
> - err = -EINVAL;
> - goto err_put;
> - }
> + init_timer(&dev->timer);
> + dev->timer.data = (unsigned long)(dev);
> + dev->timer.function = dev_periodic_work;
>
> /* bus_id must be a unique name with respect to this bus TYPE
> * (NOT bus instance). That's why we need to include the bus
> @@ -1268,13 +1255,6 @@ visorbus_init(void)
> goto error;
> }
>
> - periodic_dev_workqueue = create_singlethread_workqueue("visorbus_dev");
> - if (!periodic_dev_workqueue) {
> - POSTCODE_LINUX_2(CREATE_WORKQUEUE_PC, DIAG_SEVERITY_ERR);
> - err = -ENOMEM;
> - goto error;
> - }
> -
> /* This enables us to receive notifications when devices appear for
> * which this service partition is to be a server for.
> */
> @@ -1297,10 +1277,6 @@ visorbus_exit(void)
> visorchipset_register_busdev(NULL, NULL, NULL);
> remove_all_visor_devices();
>
> - flush_workqueue(periodic_dev_workqueue); /* better not be any work! */
> - destroy_workqueue(periodic_dev_workqueue);
> - periodic_dev_workqueue = NULL;
> -
> list_for_each_safe(listentry, listtmp, &list_all_bus_instances) {
> struct visor_device *dev = list_entry(listentry,
> struct visor_device,
> --
> 1.9.1
>
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