kernel/rcu/tiny.c

   1 /*
   2  * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright IBM Corporation, 2008
  19  *
  20  * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  21  *
  22  * For detailed explanation of Read-Copy Update mechanism see -
  23  *              Documentation/RCU
  24  */
  25 #include <linux/completion.h>
  26 #include <linux/interrupt.h>
  27 #include <linux/notifier.h>
  28 #include <linux/rcupdate.h>
  29 #include <linux/kernel.h>
  30 #include <linux/export.h>
  31 #include <linux/mutex.h>
  32 #include <linux/sched.h>
  33 #include <linux/types.h>
  34 #include <linux/init.h>
  35 #include <linux/time.h>
  36 #include <linux/cpu.h>
  37 #include <linux/prefetch.h>
  38 #include <linux/ftrace_event.h>
  39
  40 #ifdef CONFIG_RCU_TRACE
  41 #include <trace/events/rcu.h>
  42 #endif /* #else #ifdef CONFIG_RCU_TRACE */
  43
  44 #include "rcu.h"
  45
  46 /* Forward declarations for tiny_plugin.h. */
  47 struct rcu_ctrlblk;
  48 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
  49 static void rcu_process_callbacks(struct softirq_action *unused);
  50 static void __call_rcu(struct rcu_head *head,
  51                        void (*func)(struct rcu_head *rcu),
  52                        struct rcu_ctrlblk *rcp);
  53
  54 static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
  55
  56 #include "tiny_plugin.h"
  57
  58 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
  59 static void rcu_idle_enter_common(long long newval)
  60 {
  61         if (newval) {
  62                 RCU_TRACE(trace_rcu_dyntick(TPS("--="),
  63                                             rcu_dynticks_nesting, newval));
  64                 rcu_dynticks_nesting = newval;
  65                 return;
  66         }
  67         RCU_TRACE(trace_rcu_dyntick(TPS("Start"),
  68                                     rcu_dynticks_nesting, newval));
  69         if (!is_idle_task(current)) {
  70                 struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
  71
  72                 RCU_TRACE(trace_rcu_dyntick(TPS("Entry error: not idle task"),
  73                                             rcu_dynticks_nesting, newval));
  74                 ftrace_dump(DUMP_ALL);
  75                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
  76                           current->pid, current->comm,
  77                           idle->pid, idle->comm); /* must be idle task! */
  78         }
  79         rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
  80         barrier();
  81         rcu_dynticks_nesting = newval;
  82 }
  83
  84 /*
  85  * Enter idle, which is an extended quiescent state if we have fully
  86  * entered that mode (i.e., if the new value of dynticks_nesting is zero).
  87  */
  88 void rcu_idle_enter(void)
  89 {
  90         unsigned long flags;
  91         long long newval;
  92
  93         local_irq_save(flags);
  94         WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
  95         if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
  96             DYNTICK_TASK_NEST_VALUE)
  97                 newval = 0;
  98         else
  99                 newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
 100         rcu_idle_enter_common(newval);
 101         local_irq_restore(flags);
 102 }
 103 EXPORT_SYMBOL_GPL(rcu_idle_enter);
 104
 105 /*
 106  * Exit an interrupt handler towards idle.
 107  */
 108 void rcu_irq_exit(void)
 109 {
 110         unsigned long flags;
 111         long long newval;
 112
 113         local_irq_save(flags);
 114         newval = rcu_dynticks_nesting - 1;
 115         WARN_ON_ONCE(newval < 0);
 116         rcu_idle_enter_common(newval);
 117         local_irq_restore(flags);
 118 }
 119 EXPORT_SYMBOL_GPL(rcu_irq_exit);
 120
 121 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
 122 static void rcu_idle_exit_common(long long oldval)
 123 {
 124         if (oldval) {
 125                 RCU_TRACE(trace_rcu_dyntick(TPS("++="),
 126                                             oldval, rcu_dynticks_nesting));
 127                 return;
 128         }
 129         RCU_TRACE(trace_rcu_dyntick(TPS("End"), oldval, rcu_dynticks_nesting));
 130         if (!is_idle_task(current)) {
 131                 struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
 132
 133                 RCU_TRACE(trace_rcu_dyntick(TPS("Exit error: not idle task"),
 134                           oldval, rcu_dynticks_nesting));
 135                 ftrace_dump(DUMP_ALL);
 136                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
 137                           current->pid, current->comm,
 138                           idle->pid, idle->comm); /* must be idle task! */
 139         }
 140 }
 141
 142 /*
 143  * Exit idle, so that we are no longer in an extended quiescent state.
 144  */
 145 void rcu_idle_exit(void)
 146 {
 147         unsigned long flags;
 148         long long oldval;
 149
 150         local_irq_save(flags);
 151         oldval = rcu_dynticks_nesting;
 152         WARN_ON_ONCE(rcu_dynticks_nesting < 0);
 153         if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
 154                 rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
 155         else
 156                 rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 157         rcu_idle_exit_common(oldval);
 158         local_irq_restore(flags);
 159 }
 160 EXPORT_SYMBOL_GPL(rcu_idle_exit);
 161
 162 /*
 163  * Enter an interrupt handler, moving away from idle.
 164  */
 165 void rcu_irq_enter(void)
 166 {
 167         unsigned long flags;
 168         long long oldval;
 169
 170         local_irq_save(flags);
 171         oldval = rcu_dynticks_nesting;
 172         rcu_dynticks_nesting++;
 173         WARN_ON_ONCE(rcu_dynticks_nesting == 0);
 174         rcu_idle_exit_common(oldval);
 175         local_irq_restore(flags);
 176 }
 177 EXPORT_SYMBOL_GPL(rcu_irq_enter);
 178
 179 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
 180
 181 /*
 182  * Test whether RCU thinks that the current CPU is idle.
 183  */
 184 bool __rcu_is_watching(void)
 185 {
 186         return rcu_dynticks_nesting;
 187 }
 188 EXPORT_SYMBOL(__rcu_is_watching);
 189
 190 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
 191
 192 /*
 193  * Test whether the current CPU was interrupted from idle.  Nested
 194  * interrupts don't count, we must be running at the first interrupt
 195  * level.
 196  */
 197 static int rcu_is_cpu_rrupt_from_idle(void)
 198 {
 199         return rcu_dynticks_nesting <= 1;
 200 }
 201
 202 /*
 203  * Helper function for rcu_sched_qs() and rcu_bh_qs().
 204  * Also irqs are disabled to avoid confusion due to interrupt handlers
 205  * invoking call_rcu().
 206  */
 207 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 208 {
 209         RCU_TRACE(reset_cpu_stall_ticks(rcp));
 210         if (rcp->rcucblist != NULL &&
 211             rcp->donetail != rcp->curtail) {
 212                 rcp->donetail = rcp->curtail;
 213                 return 1;
 214         }
 215
 216         return 0;
 217 }
 218
 219 /*
 220  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 221  * are at it, given that any rcu quiescent state is also an rcu_bh
 222  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 223  */
 224 void rcu_sched_qs(int cpu)
 225 {
 226         unsigned long flags;
 227
 228         local_irq_save(flags);
 229         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 230             rcu_qsctr_help(&rcu_bh_ctrlblk))
 231                 raise_softirq(RCU_SOFTIRQ);
 232         local_irq_restore(flags);
 233 }
 234
 235 /*
 236  * Record an rcu_bh quiescent state.
 237  */
 238 void rcu_bh_qs(int cpu)
 239 {
 240         unsigned long flags;
 241
 242         local_irq_save(flags);
 243         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 244                 raise_softirq(RCU_SOFTIRQ);
 245         local_irq_restore(flags);
 246 }
 247
 248 /*
 249  * Check to see if the scheduling-clock interrupt came from an extended
 250  * quiescent state, and, if so, tell RCU about it.  This function must
 251  * be called from hardirq context.  It is normally called from the
 252  * scheduling-clock interrupt.
 253  */
 254 void rcu_check_callbacks(int cpu, int user)
 255 {
 256         RCU_TRACE(check_cpu_stalls());
 257         if (user || rcu_is_cpu_rrupt_from_idle())
 258                 rcu_sched_qs(cpu);
 259         else if (!in_softirq())
 260                 rcu_bh_qs(cpu);
 261 }
 262
 263 /*
 264  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 265  * whose grace period has elapsed.
 266  */
 267 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 268 {
 269         const char *rn = NULL;
 270         struct rcu_head *next, *list;
 271         unsigned long flags;
 272         RCU_TRACE(int cb_count = 0);
 273
 274         /* If no RCU callbacks ready to invoke, just return. */
 275         if (&rcp->rcucblist == rcp->donetail) {
 276                 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
 277                 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 278                                               !!ACCESS_ONCE(rcp->rcucblist),
 279                                               need_resched(),
 280                                               is_idle_task(current),
 281                                               false));
 282                 return;
 283         }
 284
 285         /* Move the ready-to-invoke callbacks to a local list. */
 286         local_irq_save(flags);
 287         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 288         list = rcp->rcucblist;
 289         rcp->rcucblist = *rcp->donetail;
 290         *rcp->donetail = NULL;
 291         if (rcp->curtail == rcp->donetail)
 292                 rcp->curtail = &rcp->rcucblist;
 293         rcp->donetail = &rcp->rcucblist;
 294         local_irq_restore(flags);
 295
 296         /* Invoke the callbacks on the local list. */
 297         RCU_TRACE(rn = rcp->name);
 298         while (list) {
 299                 next = list->next;
 300                 prefetch(next);
 301                 debug_rcu_head_unqueue(list);
 302                 local_bh_disable();
 303                 __rcu_reclaim(rn, list);
 304                 local_bh_enable();
 305                 list = next;
 306                 RCU_TRACE(cb_count++);
 307         }
 308         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 309         RCU_TRACE(trace_rcu_batch_end(rcp->name,
 310                                       cb_count, 0, need_resched(),
 311                                       is_idle_task(current),
 312                                       false));
 313 }
 314
 315 static void rcu_process_callbacks(struct softirq_action *unused)
 316 {
 317         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 318         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 319 }
 320
 321 /*
 322  * Wait for a grace period to elapse.  But it is illegal to invoke
 323  * synchronize_sched() from within an RCU read-side critical section.
 324  * Therefore, any legal call to synchronize_sched() is a quiescent
 325  * state, and so on a UP system, synchronize_sched() need do nothing.
 326  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 327  * benefits of doing might_sleep() to reduce latency.)
 328  *
 329  * Cool, huh?  (Due to Josh Triplett.)
 330  *
 331  * But we want to make this a static inline later.  The cond_resched()
 332  * currently makes this problematic.
 333  */
 334 void synchronize_sched(void)
 335 {
 336         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 337                            !lock_is_held(&rcu_lock_map) &&
 338                            !lock_is_held(&rcu_sched_lock_map),
 339                            "Illegal synchronize_sched() in RCU read-side critical section");
 340         cond_resched();
 341 }
 342 EXPORT_SYMBOL_GPL(synchronize_sched);
 343
 344 /*
 345  * Helper function for call_rcu() and call_rcu_bh().
 346  */
 347 static void __call_rcu(struct rcu_head *head,
 348                        void (*func)(struct rcu_head *rcu),
 349                        struct rcu_ctrlblk *rcp)
 350 {
 351         unsigned long flags;
 352
 353         debug_rcu_head_queue(head);
 354         head->func = func;
 355         head->next = NULL;
 356
 357         local_irq_save(flags);
 358         *rcp->curtail = head;
 359         rcp->curtail = &head->next;
 360         RCU_TRACE(rcp->qlen++);
 361         local_irq_restore(flags);
 362 }
 363
 364 /*
 365  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 366  * period.  But since we have but one CPU, that would be after any
 367  * quiescent state.
 368  */
 369 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 370 {
 371         __call_rcu(head, func, &rcu_sched_ctrlblk);
 372 }
 373 EXPORT_SYMBOL_GPL(call_rcu_sched);
 374
 375 /*
 376  * Post an RCU bottom-half callback to be invoked after any subsequent
 377  * quiescent state.
 378  */
 379 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 380 {
 381         __call_rcu(head, func, &rcu_bh_ctrlblk);
 382 }
 383 EXPORT_SYMBOL_GPL(call_rcu_bh);
 384
 385 void rcu_init(void)
 386 {
 387         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 388 }