1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
/* periodic_work.c
*
* Copyright (C) 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 {
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) < 0) {
ERRDEV(pw->devnam, "queue_delayed_work failed!");
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) {
ERRDEV(pw->devnam,
"dev_start_periodic_work failed!");
rc = FALSE;
goto unlock;
}
INIT_DELAYED_WORK(&pw->work, &periodic_work_func);
if (queue_delayed_work(pw->workqueue, &pw->work,
pw->jiffy_interval) < 0) {
ERRDEV(pw->devnam, "%s queue_delayed_work failed!", __func__);
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.
*/
ASSERT(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);
WARNDEV(pw->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(&pw->lock);
} else {
pw->want_to_stop = FALSE;
}
}
write_unlock(&pw->lock);
return stopped_something;
}
EXPORT_SYMBOL_GPL(visor_periodic_work_stop);
|
