| /* 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); |