Ken Cox | 9d9baad | 2014-03-04 07:58:05 -0600 | [diff] [blame] | 1 | /* periodic_work.c |
| 2 | * |
| 3 | * Copyright © 2010 - 2013 UNISYS CORPORATION |
| 4 | * All rights reserved. |
| 5 | * |
| 6 | * This program is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License as published by |
| 8 | * the Free Software Foundation; either version 2 of the License, or (at |
| 9 | * your option) any later version. |
| 10 | * |
| 11 | * This program is distributed in the hope that it will be useful, but |
| 12 | * WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or |
| 14 | * NON INFRINGEMENT. See the GNU General Public License for more |
| 15 | * details. |
| 16 | */ |
| 17 | |
| 18 | /* |
| 19 | * Helper functions to schedule periodic work in Linux kernel mode. |
| 20 | */ |
| 21 | |
| 22 | #include "uniklog.h" |
| 23 | #include "timskmod.h" |
| 24 | #include "periodic_work.h" |
| 25 | |
| 26 | #define MYDRVNAME "periodic_work" |
| 27 | |
| 28 | |
| 29 | |
| 30 | struct PERIODIC_WORK_Tag { |
| 31 | rwlock_t lock; |
| 32 | struct delayed_work work; |
| 33 | void (*workfunc)(void *); |
| 34 | void *workfuncarg; |
| 35 | BOOL is_scheduled; |
| 36 | BOOL want_to_stop; |
| 37 | ulong jiffy_interval; |
| 38 | struct workqueue_struct *workqueue; |
| 39 | const char *devnam; |
| 40 | }; |
| 41 | |
| 42 | |
| 43 | |
| 44 | static void periodic_work_func(struct work_struct *work) |
| 45 | { |
| 46 | PERIODIC_WORK *periodic_work = |
| 47 | container_of(work, struct PERIODIC_WORK_Tag, work.work); |
| 48 | (*periodic_work->workfunc)(periodic_work->workfuncarg); |
| 49 | } |
| 50 | |
| 51 | |
| 52 | |
| 53 | PERIODIC_WORK *periodic_work_create(ulong jiffy_interval, |
| 54 | struct workqueue_struct *workqueue, |
| 55 | void (*workfunc)(void *), |
| 56 | void *workfuncarg, |
| 57 | const char *devnam) |
| 58 | { |
| 59 | PERIODIC_WORK *periodic_work = kmalloc(sizeof(PERIODIC_WORK), |
| 60 | GFP_KERNEL|__GFP_NORETRY); |
| 61 | if (periodic_work == NULL) { |
| 62 | ERRDRV("periodic_work allocation failed "); |
| 63 | return NULL; |
| 64 | } |
| 65 | memset(periodic_work, '\0', sizeof(PERIODIC_WORK)); |
| 66 | rwlock_init(&periodic_work->lock); |
| 67 | periodic_work->jiffy_interval = jiffy_interval; |
| 68 | periodic_work->workqueue = workqueue; |
| 69 | periodic_work->workfunc = workfunc; |
| 70 | periodic_work->workfuncarg = workfuncarg; |
| 71 | periodic_work->devnam = devnam; |
| 72 | return periodic_work; |
| 73 | } |
| 74 | EXPORT_SYMBOL_GPL(periodic_work_create); |
| 75 | |
| 76 | |
| 77 | |
| 78 | void periodic_work_destroy(PERIODIC_WORK *periodic_work) |
| 79 | { |
| 80 | if (periodic_work == NULL) |
| 81 | return; |
| 82 | kfree(periodic_work); |
| 83 | } |
| 84 | EXPORT_SYMBOL_GPL(periodic_work_destroy); |
| 85 | |
| 86 | |
| 87 | |
| 88 | /** Call this from your periodic work worker function to schedule the next |
| 89 | * call. |
| 90 | * If this function returns FALSE, there was a failure and the |
| 91 | * periodic work is no longer scheduled |
| 92 | */ |
| 93 | BOOL periodic_work_nextperiod(PERIODIC_WORK *periodic_work) |
| 94 | { |
| 95 | BOOL rc = FALSE; |
| 96 | write_lock(&periodic_work->lock); |
| 97 | if (periodic_work->want_to_stop) { |
| 98 | periodic_work->is_scheduled = FALSE; |
| 99 | periodic_work->want_to_stop = FALSE; |
| 100 | RETBOOL(TRUE); /* yes, TRUE; see periodic_work_stop() */ |
| 101 | } else if (queue_delayed_work(periodic_work->workqueue, |
| 102 | &periodic_work->work, |
| 103 | periodic_work->jiffy_interval) < 0) { |
| 104 | ERRDEV(periodic_work->devnam, "queue_delayed_work failed!"); |
| 105 | periodic_work->is_scheduled = FALSE; |
| 106 | RETBOOL(FALSE); |
| 107 | } |
| 108 | RETBOOL(TRUE); |
| 109 | Away: |
| 110 | write_unlock(&periodic_work->lock); |
| 111 | return rc; |
| 112 | } |
| 113 | EXPORT_SYMBOL_GPL(periodic_work_nextperiod); |
| 114 | |
| 115 | |
| 116 | |
| 117 | /** This function returns TRUE iff new periodic work was actually started. |
| 118 | * If this function returns FALSE, then no work was started |
| 119 | * (either because it was already started, or because of a failure). |
| 120 | */ |
| 121 | BOOL periodic_work_start(PERIODIC_WORK *periodic_work) |
| 122 | { |
| 123 | BOOL rc = FALSE; |
| 124 | |
| 125 | write_lock(&periodic_work->lock); |
| 126 | if (periodic_work->is_scheduled) |
| 127 | RETBOOL(FALSE); |
| 128 | if (periodic_work->want_to_stop) { |
| 129 | ERRDEV(periodic_work->devnam, |
| 130 | "dev_start_periodic_work failed!"); |
| 131 | RETBOOL(FALSE); |
| 132 | } |
| 133 | INIT_DELAYED_WORK(&periodic_work->work, &periodic_work_func); |
| 134 | if (queue_delayed_work(periodic_work->workqueue, |
| 135 | &periodic_work->work, |
| 136 | periodic_work->jiffy_interval) < 0) { |
| 137 | ERRDEV(periodic_work->devnam, |
| 138 | "%s queue_delayed_work failed!", __func__); |
| 139 | RETBOOL(FALSE); |
| 140 | } |
| 141 | periodic_work->is_scheduled = TRUE; |
| 142 | RETBOOL(TRUE); |
| 143 | Away: |
| 144 | write_unlock(&periodic_work->lock); |
| 145 | return rc; |
| 146 | |
| 147 | } |
| 148 | EXPORT_SYMBOL_GPL(periodic_work_start); |
| 149 | |
| 150 | |
| 151 | |
| 152 | |
| 153 | /** This function returns TRUE iff your call actually stopped the periodic |
| 154 | * work. |
| 155 | * |
| 156 | * -- PAY ATTENTION... this is important -- |
| 157 | * |
| 158 | * NO NO #1 |
| 159 | * |
| 160 | * Do NOT call this function from some function that is running on the |
| 161 | * same workqueue as the work you are trying to stop might be running |
| 162 | * on! If you violate this rule, periodic_work_stop() MIGHT work, but it |
| 163 | * also MIGHT get hung up in an infinite loop saying |
| 164 | * "waiting for delayed work...". This will happen if the delayed work |
| 165 | * you are trying to cancel has been put in the workqueue list, but can't |
| 166 | * run yet because we are running that same workqueue thread right now. |
| 167 | * |
| 168 | * Bottom line: If you need to call periodic_work_stop() from a workitem, |
| 169 | * be sure the workitem is on a DIFFERENT workqueue than the workitem that |
| 170 | * you are trying to cancel. |
| 171 | * |
| 172 | * If I could figure out some way to check for this "no no" condition in |
| 173 | * the code, I would. It would have saved me the trouble of writing this |
| 174 | * long comment. And also, don't think this is some "theoretical" race |
| 175 | * condition. It is REAL, as I have spent the day chasing it. |
| 176 | * |
| 177 | * NO NO #2 |
| 178 | * |
| 179 | * Take close note of the locks that you own when you call this function. |
| 180 | * You must NOT own any locks that are needed by the periodic work |
| 181 | * function that is currently installed. If you DO, a deadlock may result, |
| 182 | * because stopping the periodic work often involves waiting for the last |
| 183 | * iteration of the periodic work function to complete. Again, if you hit |
| 184 | * this deadlock, you will get hung up in an infinite loop saying |
| 185 | * "waiting for delayed work...". |
| 186 | */ |
| 187 | BOOL periodic_work_stop(PERIODIC_WORK *periodic_work) |
| 188 | { |
| 189 | BOOL stopped_something = FALSE; |
| 190 | |
| 191 | write_lock(&periodic_work->lock); |
| 192 | stopped_something = periodic_work->is_scheduled && |
| 193 | (!periodic_work->want_to_stop); |
| 194 | while (periodic_work->is_scheduled) { |
| 195 | periodic_work->want_to_stop = TRUE; |
| 196 | if (cancel_delayed_work(&periodic_work->work)) { |
| 197 | /* We get here if the delayed work was pending as |
| 198 | * delayed work, but was NOT run. |
| 199 | */ |
| 200 | ASSERT(periodic_work->is_scheduled); |
| 201 | periodic_work->is_scheduled = FALSE; |
| 202 | } else { |
| 203 | /* If we get here, either the delayed work: |
| 204 | * - was run, OR, |
| 205 | * - is running RIGHT NOW on another processor, OR, |
| 206 | * - wasn't even scheduled (there is a miniscule |
| 207 | * timing window where this could be the case) |
| 208 | * flush_workqueue() would make sure it is finished |
| 209 | * executing, but that still isn't very useful, which |
| 210 | * explains the loop... |
| 211 | */ |
| 212 | } |
| 213 | if (periodic_work->is_scheduled) { |
| 214 | write_unlock(&periodic_work->lock); |
| 215 | WARNDEV(periodic_work->devnam, |
| 216 | "waiting for delayed work..."); |
| 217 | /* We rely on the delayed work function running here, |
| 218 | * and eventually calling periodic_work_nextperiod(), |
| 219 | * which will see that want_to_stop is set, and |
| 220 | * subsequently clear is_scheduled. |
| 221 | */ |
| 222 | SLEEPJIFFIES(10); |
| 223 | write_lock(&periodic_work->lock); |
| 224 | } else |
| 225 | periodic_work->want_to_stop = FALSE; |
| 226 | } |
| 227 | write_unlock(&periodic_work->lock); |
| 228 | return stopped_something; |
| 229 | } |
| 230 | EXPORT_SYMBOL_GPL(periodic_work_stop); |