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[PATCH v3 11/30] staging: unisys: visorbus: use kernel timer instead of workqueue

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  [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer instead of workqueue David Kershner <david.kershner@unisys.com> - 2016-06-04 19:30 +0200
    Re: [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer  instead of workqueue Neil Horman <nhorman@redhat.com> - 2016-06-07 15:50 +0200
      RE: [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer  instead of workqueue "Sell, Timothy C" <Timothy.Sell@unisys.com> - 2016-06-07 15:50 +0200
        Re: [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer  instead of workqueue Neil Horman <nhorman@redhat.com> - 2016-06-07 16:00 +0200

#1413815 — [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer instead of workqueue

From: Tim Sell <Timothy.Sell@unisys.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@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.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);
-	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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#1416196 — 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@unisys.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@unisys.com>
> Signed-off-by: David Kershner <david.kershner@unisys.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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#1416204 — RE: [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer instead of workqueue

> -----Original Message-----
> From: Neil Horman [mailto:nhorman@redhat.com]
> Sent: Tuesday, June 07, 2016 9:40 AM
> To: Kershner, David A
> Cc: corbet@lwn.net; tglx@linutronix.de; mingo@redhat.com;
> hpa@zytor.com; gregkh@linuxfoundation.org; Arfvidson, Erik; Sell, Timothy
> C; hofrat@osadl.org; dzickus@redhat.com; jes.sorensen@redhat.com;
> Curtin, Alexander Paul; janani.rvchndrn@gmail.com;
> sudipm.mukherjee@gmail.com; prarit@redhat.com; Binder, David Anthony;
> dan.j.williams@intel.com; linux-kernel@vger.kernel.org; linux-
> doc@vger.kernel.org; driverdev-devel@linuxdriverproject.org; *S-Par-
> Maintainer
> 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@unisys.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@unisys.com>
> > Signed-off-by: David Kershner <david.kershner@unisys.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.

visorinput_channel_interrupt() USED to use down_write(), but I removed
this in the previous patch in this set ([PATCH v3 10/30] staging: unisys:
visorinput: remove unnecessary locking).  None of the other
channel_interrupt functions use non-atomic locking.  (It's possible they
USED TO, but not anymore.)

Tim Sell

> 
> > -	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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#1416221 — Re: [PATCH v3 11/30] staging: unisys: visorbus: use kernel timer instead of workqueue

On Tue, Jun 07, 2016 at 01:47:13PM +0000, Sell, Timothy C wrote:
> > -----Original Message-----
> > From: Neil Horman [mailto:nhorman@redhat.com]
> > Sent: Tuesday, June 07, 2016 9:40 AM
> > To: Kershner, David A
> > Cc: corbet@lwn.net; tglx@linutronix.de; mingo@redhat.com;
> > hpa@zytor.com; gregkh@linuxfoundation.org; Arfvidson, Erik; Sell, Timothy
> > C; hofrat@osadl.org; dzickus@redhat.com; jes.sorensen@redhat.com;
> > Curtin, Alexander Paul; janani.rvchndrn@gmail.com;
> > sudipm.mukherjee@gmail.com; prarit@redhat.com; Binder, David Anthony;
> > dan.j.williams@intel.com; linux-kernel@vger.kernel.org; linux-
> > doc@vger.kernel.org; driverdev-devel@linuxdriverproject.org; *S-Par-
> > Maintainer
> > 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@unisys.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@unisys.com>
> > > Signed-off-by: David Kershner <david.kershner@unisys.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.
> 
> visorinput_channel_interrupt() USED to use down_write(), but I removed
> this in the previous patch in this set ([PATCH v3 10/30] staging: unisys:
> visorinput: remove unnecessary locking).  None of the other
> channel_interrupt functions use non-atomic locking.  (It's possible they
> USED TO, but not anymore.)
> 
> Tim Sell
> 
Ah, so you did, thanks for the clarification.

Neil

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