+++ /dev/null
-/* periodic_work.c
- *
- * Copyright (C) 2010 - 2015 UNISYS CORPORATION
- * All rights reserved.
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms and conditions of the GNU General Public License,
- * version 2, as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
- * NON INFRINGEMENT. See the GNU General Public License for more
- * details.
- */
-
-/*
- * Helper functions to schedule periodic work in Linux kernel mode.
- */
-#include <linux/sched.h>
-
-#include "periodic_work.h"
-
-#define MYDRVNAME "periodic_work"
-
-struct periodic_work {
- rwlock_t lock;
- struct delayed_work work;
- void (*workfunc)(void *);
- void *workfuncarg;
- bool is_scheduled;
- bool want_to_stop;
- ulong jiffy_interval;
- struct workqueue_struct *workqueue;
- const char *devnam;
-};
-
-static void periodic_work_func(struct work_struct *work)
-{
- struct periodic_work *pw;
-
- pw = container_of(work, struct periodic_work, work.work);
- (*pw->workfunc)(pw->workfuncarg);
-}
-
-struct periodic_work
-*visor_periodic_work_create(ulong jiffy_interval,
- struct workqueue_struct *workqueue,
- void (*workfunc)(void *),
- void *workfuncarg,
- const char *devnam)
-{
- struct periodic_work *pw;
-
- pw = kzalloc(sizeof(*pw), GFP_KERNEL | __GFP_NORETRY);
- if (!pw)
- return NULL;
-
- rwlock_init(&pw->lock);
- pw->jiffy_interval = jiffy_interval;
- pw->workqueue = workqueue;
- pw->workfunc = workfunc;
- pw->workfuncarg = workfuncarg;
- pw->devnam = devnam;
- return pw;
-}
-EXPORT_SYMBOL_GPL(visor_periodic_work_create);
-
-void visor_periodic_work_destroy(struct periodic_work *pw)
-{
- kfree(pw);
-}
-EXPORT_SYMBOL_GPL(visor_periodic_work_destroy);
-
-/** Call this from your periodic work worker function to schedule the next
- * call.
- * If this function returns false, there was a failure and the
- * periodic work is no longer scheduled
- */
-bool visor_periodic_work_nextperiod(struct periodic_work *pw)
-{
- bool rc = false;
-
- write_lock(&pw->lock);
- if (pw->want_to_stop) {
- pw->is_scheduled = false;
- pw->want_to_stop = false;
- rc = true; /* yes, true; see visor_periodic_work_stop() */
- goto unlock;
- } else if (!queue_delayed_work(pw->workqueue, &pw->work,
- pw->jiffy_interval)) {
- pw->is_scheduled = false;
- rc = false;
- goto unlock;
- }
- rc = true;
-unlock:
- write_unlock(&pw->lock);
- return rc;
-}
-EXPORT_SYMBOL_GPL(visor_periodic_work_nextperiod);
-
-/** This function returns true iff new periodic work was actually started.
- * If this function returns false, then no work was started
- * (either because it was already started, or because of a failure).
- */
-bool visor_periodic_work_start(struct periodic_work *pw)
-{
- bool rc = false;
-
- write_lock(&pw->lock);
- if (pw->is_scheduled) {
- rc = false;
- goto unlock;
- }
- if (pw->want_to_stop) {
- rc = false;
- goto unlock;
- }
- INIT_DELAYED_WORK(&pw->work, &periodic_work_func);
- if (!queue_delayed_work(pw->workqueue, &pw->work,
- pw->jiffy_interval)) {
- rc = false;
- goto unlock;
- }
- pw->is_scheduled = true;
- rc = true;
-unlock:
- write_unlock(&pw->lock);
- return rc;
-}
-EXPORT_SYMBOL_GPL(visor_periodic_work_start);
-
-/** This function returns true iff your call actually stopped the periodic
- * work.
- *
- * -- PAY ATTENTION... this is important --
- *
- * NO NO #1
- *
- * Do NOT call this function from some function that is running on the
- * same workqueue as the work you are trying to stop might be running
- * on! If you violate this rule, visor_periodic_work_stop() MIGHT work,
- * but it also MIGHT get hung up in an infinite loop saying
- * "waiting for delayed work...". This will happen if the delayed work
- * you are trying to cancel has been put in the workqueue list, but can't
- * run yet because we are running that same workqueue thread right now.
- *
- * Bottom line: If you need to call visor_periodic_work_stop() from a
- * workitem, be sure the workitem is on a DIFFERENT workqueue than the
- * workitem that you are trying to cancel.
- *
- * If I could figure out some way to check for this "no no" condition in
- * the code, I would. It would have saved me the trouble of writing this
- * long comment. And also, don't think this is some "theoretical" race
- * condition. It is REAL, as I have spent the day chasing it.
- *
- * NO NO #2
- *
- * Take close note of the locks that you own when you call this function.
- * You must NOT own any locks that are needed by the periodic work
- * function that is currently installed. If you DO, a deadlock may result,
- * because stopping the periodic work often involves waiting for the last
- * iteration of the periodic work function to complete. Again, if you hit
- * this deadlock, you will get hung up in an infinite loop saying
- * "waiting for delayed work...".
- */
-bool visor_periodic_work_stop(struct periodic_work *pw)
-{
- bool stopped_something = false;
-
- write_lock(&pw->lock);
- stopped_something = pw->is_scheduled && (!pw->want_to_stop);
- while (pw->is_scheduled) {
- pw->want_to_stop = true;
- if (cancel_delayed_work(&pw->work)) {
- /* We get here if the delayed work was pending as
- * delayed work, but was NOT run.
- */
- WARN_ON(!pw->is_scheduled);
- pw->is_scheduled = false;
- } else {
- /* If we get here, either the delayed work:
- * - was run, OR,
- * - is running RIGHT NOW on another processor, OR,
- * - wasn't even scheduled (there is a miniscule
- * timing window where this could be the case)
- * flush_workqueue() would make sure it is finished
- * executing, but that still isn't very useful, which
- * explains the loop...
- */
- }
- if (pw->is_scheduled) {
- write_unlock(&pw->lock);
- schedule_timeout_interruptible(msecs_to_jiffies(10));
- write_lock(&pw->lock);
- } else {
- pw->want_to_stop = false;
- }
- }
- write_unlock(&pw->lock);
- return stopped_something;
-}
-EXPORT_SYMBOL_GPL(visor_periodic_work_stop);
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