diff options
Diffstat (limited to 'drivers/staging/unisys/visorutil/periodic_work.c')
-rw-r--r-- | drivers/staging/unisys/visorutil/periodic_work.c | 236 |
1 files changed, 236 insertions, 0 deletions
diff --git a/drivers/staging/unisys/visorutil/periodic_work.c b/drivers/staging/unisys/visorutil/periodic_work.c new file mode 100644 index 000000000000..0670a3174682 --- /dev/null +++ b/drivers/staging/unisys/visorutil/periodic_work.c @@ -0,0 +1,236 @@ +/* periodic_work.c + * + * Copyright © 2010 - 2013 UNISYS CORPORATION + * All rights reserved. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or (at + * your option) any later version. + * + * 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 "uniklog.h" +#include "timskmod.h" +#include "periodic_work.h" + +#define MYDRVNAME "periodic_work" + + + +struct PERIODIC_WORK_Tag { + 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) +{ + PERIODIC_WORK *periodic_work = + container_of(work, struct PERIODIC_WORK_Tag, work.work); + (*periodic_work->workfunc)(periodic_work->workfuncarg); +} + + + +PERIODIC_WORK *visor_periodic_work_create(ulong jiffy_interval, + struct workqueue_struct *workqueue, + void (*workfunc)(void *), + void *workfuncarg, + const char *devnam) +{ + PERIODIC_WORK *periodic_work = kzalloc(sizeof(PERIODIC_WORK), + GFP_KERNEL | __GFP_NORETRY); + if (periodic_work == NULL) { + ERRDRV("periodic_work allocation failed "); + return NULL; + } + rwlock_init(&periodic_work->lock); + periodic_work->jiffy_interval = jiffy_interval; + periodic_work->workqueue = workqueue; + periodic_work->workfunc = workfunc; + periodic_work->workfuncarg = workfuncarg; + periodic_work->devnam = devnam; + return periodic_work; +} +EXPORT_SYMBOL_GPL(visor_periodic_work_create); + + + +void visor_periodic_work_destroy(PERIODIC_WORK *periodic_work) +{ + if (periodic_work == NULL) + return; + kfree(periodic_work); +} +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(PERIODIC_WORK *periodic_work) +{ + BOOL rc = FALSE; + write_lock(&periodic_work->lock); + if (periodic_work->want_to_stop) { + periodic_work->is_scheduled = FALSE; + periodic_work->want_to_stop = FALSE; + rc = TRUE; /* yes, TRUE; see visor_periodic_work_stop() */ + goto Away; + } else if (queue_delayed_work(periodic_work->workqueue, + &periodic_work->work, + periodic_work->jiffy_interval) < 0) { + ERRDEV(periodic_work->devnam, "queue_delayed_work failed!"); + periodic_work->is_scheduled = FALSE; + rc = FALSE; + goto Away; + } + rc = TRUE; +Away: + write_unlock(&periodic_work->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(PERIODIC_WORK *periodic_work) +{ + BOOL rc = FALSE; + + write_lock(&periodic_work->lock); + if (periodic_work->is_scheduled) { + rc = FALSE; + goto Away; + } + if (periodic_work->want_to_stop) { + ERRDEV(periodic_work->devnam, + "dev_start_periodic_work failed!"); + rc = FALSE; + goto Away; + } + INIT_DELAYED_WORK(&periodic_work->work, &periodic_work_func); + if (queue_delayed_work(periodic_work->workqueue, + &periodic_work->work, + periodic_work->jiffy_interval) < 0) { + ERRDEV(periodic_work->devnam, + "%s queue_delayed_work failed!", __func__); + rc = FALSE; + goto Away; + } + periodic_work->is_scheduled = TRUE; + rc = TRUE; +Away: + write_unlock(&periodic_work->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(PERIODIC_WORK *periodic_work) +{ + BOOL stopped_something = FALSE; + + write_lock(&periodic_work->lock); + stopped_something = periodic_work->is_scheduled && + (!periodic_work->want_to_stop); + while (periodic_work->is_scheduled) { + periodic_work->want_to_stop = TRUE; + if (cancel_delayed_work(&periodic_work->work)) { + /* We get here if the delayed work was pending as + * delayed work, but was NOT run. + */ + ASSERT(periodic_work->is_scheduled); + periodic_work->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 (periodic_work->is_scheduled) { + write_unlock(&periodic_work->lock); + WARNDEV(periodic_work->devnam, + "waiting for delayed work..."); + /* We rely on the delayed work function running here, + * and eventually calling + * visor_periodic_work_nextperiod(), + * which will see that want_to_stop is set, and + * subsequently clear is_scheduled. + */ + SLEEPJIFFIES(10); + write_lock(&periodic_work->lock); + } else + periodic_work->want_to_stop = FALSE; + } + write_unlock(&periodic_work->lock); + return stopped_something; +} +EXPORT_SYMBOL_GPL(visor_periodic_work_stop); |