> -----Original Message-----
> From: Neil Horman [mailto:nhor...@redhat.com]
> Sent: Tuesday, June 07, 2016 9:40 AM
> To: Kershner, David A
> Cc: cor...@lwn.net; t...@linutronix.de; mi...@redhat.com;
> h...@zytor.com; gre...@linuxfoundation.org; Arfvidson, Erik; Sell, Timothy
> C; hof...@osadl.org; dzic...@redhat.com; jes.soren...@redhat.com;
> Curtin, Alexander Paul; janani.rvchn...@gmail.com;
> sudipm.mukher...@gmail.com; pra...@redhat.com; Binder, David Anthony;
> dan.j.willi...@intel.com; linux-ker...@vger.kernel.org; linux-
> d...@vger.kernel.org; driverdev-de...@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.s...@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.s...@unisys.com>
> > Signed-off-by: David Kershner <david.kersh...@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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