f0b5c6d353
The last if statement in this function is missing brackets on the else clause. Add them. Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
218 lines
6.4 KiB
C
218 lines
6.4 KiB
C
/* periodic_work.c
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*
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* Copyright (C) 2010 - 2013 UNISYS CORPORATION
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* All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or (at
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* your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for more
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* details.
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*/
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/*
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* Helper functions to schedule periodic work in Linux kernel mode.
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*/
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#include "uniklog.h"
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#include "timskmod.h"
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#include "periodic_work.h"
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#define MYDRVNAME "periodic_work"
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struct periodic_work {
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rwlock_t lock;
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struct delayed_work work;
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void (*workfunc)(void *);
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void *workfuncarg;
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BOOL is_scheduled;
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BOOL want_to_stop;
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ulong jiffy_interval;
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struct workqueue_struct *workqueue;
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const char *devnam;
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};
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static void periodic_work_func(struct work_struct *work)
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{
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struct periodic_work *pw;
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pw = container_of(work, struct periodic_work, work.work);
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(*pw->workfunc)(pw->workfuncarg);
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}
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struct periodic_work *visor_periodic_work_create(ulong jiffy_interval,
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struct workqueue_struct *workqueue,
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void (*workfunc)(void *),
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void *workfuncarg,
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const char *devnam)
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{
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struct periodic_work *pw;
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pw = kzalloc(sizeof(*pw), GFP_KERNEL | __GFP_NORETRY);
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if (!pw)
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return NULL;
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rwlock_init(&pw->lock);
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pw->jiffy_interval = jiffy_interval;
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pw->workqueue = workqueue;
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pw->workfunc = workfunc;
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pw->workfuncarg = workfuncarg;
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pw->devnam = devnam;
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return pw;
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}
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EXPORT_SYMBOL_GPL(visor_periodic_work_create);
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void visor_periodic_work_destroy(struct periodic_work *pw)
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{
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kfree(pw);
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}
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EXPORT_SYMBOL_GPL(visor_periodic_work_destroy);
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/** Call this from your periodic work worker function to schedule the next
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* call.
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* If this function returns FALSE, there was a failure and the
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* periodic work is no longer scheduled
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*/
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BOOL visor_periodic_work_nextperiod(struct periodic_work *pw)
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{
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BOOL rc = FALSE;
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write_lock(&pw->lock);
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if (pw->want_to_stop) {
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pw->is_scheduled = FALSE;
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pw->want_to_stop = FALSE;
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rc = TRUE; /* yes, TRUE; see visor_periodic_work_stop() */
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goto unlock;
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} else if (queue_delayed_work(pw->workqueue, &pw->work,
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pw->jiffy_interval) < 0) {
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ERRDEV(pw->devnam, "queue_delayed_work failed!");
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pw->is_scheduled = FALSE;
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rc = FALSE;
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goto unlock;
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}
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rc = TRUE;
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unlock:
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write_unlock(&pw->lock);
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return rc;
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}
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EXPORT_SYMBOL_GPL(visor_periodic_work_nextperiod);
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/** This function returns TRUE iff new periodic work was actually started.
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* If this function returns FALSE, then no work was started
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* (either because it was already started, or because of a failure).
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*/
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BOOL visor_periodic_work_start(struct periodic_work *pw)
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{
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BOOL rc = FALSE;
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write_lock(&pw->lock);
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if (pw->is_scheduled) {
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rc = FALSE;
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goto unlock;
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}
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if (pw->want_to_stop) {
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ERRDEV(pw->devnam,
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"dev_start_periodic_work failed!");
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rc = FALSE;
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goto unlock;
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}
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INIT_DELAYED_WORK(&pw->work, &periodic_work_func);
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if (queue_delayed_work(pw->workqueue, &pw->work,
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pw->jiffy_interval) < 0) {
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ERRDEV(pw->devnam, "%s queue_delayed_work failed!", __func__);
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rc = FALSE;
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goto unlock;
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}
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pw->is_scheduled = TRUE;
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rc = TRUE;
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unlock:
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write_unlock(&pw->lock);
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return rc;
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}
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EXPORT_SYMBOL_GPL(visor_periodic_work_start);
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/** This function returns TRUE iff your call actually stopped the periodic
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* work.
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*
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* -- PAY ATTENTION... this is important --
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*
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* NO NO #1
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*
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* Do NOT call this function from some function that is running on the
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* same workqueue as the work you are trying to stop might be running
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* on! If you violate this rule, visor_periodic_work_stop() MIGHT work,
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* but it also MIGHT get hung up in an infinite loop saying
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* "waiting for delayed work...". This will happen if the delayed work
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* you are trying to cancel has been put in the workqueue list, but can't
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* run yet because we are running that same workqueue thread right now.
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*
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* Bottom line: If you need to call visor_periodic_work_stop() from a
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* workitem, be sure the workitem is on a DIFFERENT workqueue than the
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* workitem that you are trying to cancel.
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*
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* If I could figure out some way to check for this "no no" condition in
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* the code, I would. It would have saved me the trouble of writing this
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* long comment. And also, don't think this is some "theoretical" race
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* condition. It is REAL, as I have spent the day chasing it.
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*
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* NO NO #2
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*
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* Take close note of the locks that you own when you call this function.
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* You must NOT own any locks that are needed by the periodic work
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* function that is currently installed. If you DO, a deadlock may result,
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* because stopping the periodic work often involves waiting for the last
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* iteration of the periodic work function to complete. Again, if you hit
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* this deadlock, you will get hung up in an infinite loop saying
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* "waiting for delayed work...".
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*/
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BOOL visor_periodic_work_stop(struct periodic_work *pw)
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{
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BOOL stopped_something = FALSE;
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write_lock(&pw->lock);
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stopped_something = pw->is_scheduled && (!pw->want_to_stop);
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while (pw->is_scheduled) {
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pw->want_to_stop = TRUE;
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if (cancel_delayed_work(&pw->work)) {
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/* We get here if the delayed work was pending as
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* delayed work, but was NOT run.
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*/
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ASSERT(pw->is_scheduled);
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pw->is_scheduled = FALSE;
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} else {
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/* If we get here, either the delayed work:
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* - was run, OR,
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* - is running RIGHT NOW on another processor, OR,
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* - wasn't even scheduled (there is a miniscule
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* timing window where this could be the case)
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* flush_workqueue() would make sure it is finished
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* executing, but that still isn't very useful, which
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* explains the loop...
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*/
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}
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if (pw->is_scheduled) {
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write_unlock(&pw->lock);
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WARNDEV(pw->devnam,
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"waiting for delayed work...");
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/* We rely on the delayed work function running here,
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* and eventually calling
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* visor_periodic_work_nextperiod(),
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* which will see that want_to_stop is set, and
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* subsequently clear is_scheduled.
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*/
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SLEEPJIFFIES(10);
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write_lock(&pw->lock);
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} else {
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pw->want_to_stop = FALSE;
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}
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}
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write_unlock(&pw->lock);
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return stopped_something;
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}
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EXPORT_SYMBOL_GPL(visor_periodic_work_stop);
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