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, you can access it online at
  16  * http://www.gnu.org/licenses/gpl-2.0.html.
  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 #include "rcu.h"
  41
  42 /* Forward declarations for tiny_plugin.h. */
  43 struct rcu_ctrlblk;
  44 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
  45 static void rcu_process_callbacks(struct softirq_action *unused);
  46 static void __call_rcu(struct rcu_head *head,
  47                        void (*func)(struct rcu_head *rcu),
  48                        struct rcu_ctrlblk *rcp);
  49
  50 static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
  51
  52 #include "tiny_plugin.h"
  53
  54 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcu/tree.c. */
  55 static void rcu_idle_enter_common(long long newval)
  56 {
  57         if (newval) {
  58                 RCU_TRACE(trace_rcu_dyntick(TPS("--="),
  59                                             rcu_dynticks_nesting, newval));
  60                 rcu_dynticks_nesting = newval;
  61                 return;
  62         }
  63         RCU_TRACE(trace_rcu_dyntick(TPS("Start"),
  64                                     rcu_dynticks_nesting, newval));
  65         if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
  66                 struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
  67
  68                 RCU_TRACE(trace_rcu_dyntick(TPS("Entry error: not idle task"),
  69                                             rcu_dynticks_nesting, newval));
  70                 ftrace_dump(DUMP_ALL);
  71                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
  72                           current->pid, current->comm,
  73                           idle->pid, idle->comm); /* must be idle task! */
  74         }
  75         rcu_sched_qs(); /* implies rcu_bh_inc() */
  76         barrier();
  77         rcu_dynticks_nesting = newval;
  78 }
  79
  80 /*
  81  * Enter idle, which is an extended quiescent state if we have fully
  82  * entered that mode (i.e., if the new value of dynticks_nesting is zero).
  83  */
  84 void rcu_idle_enter(void)
  85 {
  86         unsigned long flags;
  87         long long newval;
  88
  89         local_irq_save(flags);
  90         WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
  91         if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
  92             DYNTICK_TASK_NEST_VALUE)
  93                 newval = 0;
  94         else
  95                 newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
  96         rcu_idle_enter_common(newval);
  97         local_irq_restore(flags);
  98 }
  99 EXPORT_SYMBOL_GPL(rcu_idle_enter);
 100
 101 /*
 102  * Exit an interrupt handler towards idle.
 103  */
 104 void rcu_irq_exit(void)
 105 {
 106         unsigned long flags;
 107         long long newval;
 108
 109         local_irq_save(flags);
 110         newval = rcu_dynticks_nesting - 1;
 111         WARN_ON_ONCE(newval < 0);
 112         rcu_idle_enter_common(newval);
 113         local_irq_restore(flags);
 114 }
 115 EXPORT_SYMBOL_GPL(rcu_irq_exit);
 116
 117 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcu/tree.c. */
 118 static void rcu_idle_exit_common(long long oldval)
 119 {
 120         if (oldval) {
 121                 RCU_TRACE(trace_rcu_dyntick(TPS("++="),
 122                                             oldval, rcu_dynticks_nesting));
 123                 return;
 124         }
 125         RCU_TRACE(trace_rcu_dyntick(TPS("End"), oldval, rcu_dynticks_nesting));
 126         if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
 127                 struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
 128
 129                 RCU_TRACE(trace_rcu_dyntick(TPS("Exit error: not idle task"),
 130                           oldval, rcu_dynticks_nesting));
 131                 ftrace_dump(DUMP_ALL);
 132                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
 133                           current->pid, current->comm,
 134                           idle->pid, idle->comm); /* must be idle task! */
 135         }
 136 }
 137
 138 /*
 139  * Exit idle, so that we are no longer in an extended quiescent state.
 140  */
 141 void rcu_idle_exit(void)
 142 {
 143         unsigned long flags;
 144         long long oldval;
 145
 146         local_irq_save(flags);
 147         oldval = rcu_dynticks_nesting;
 148         WARN_ON_ONCE(rcu_dynticks_nesting < 0);
 149         if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
 150                 rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
 151         else
 152                 rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 153         rcu_idle_exit_common(oldval);
 154         local_irq_restore(flags);
 155 }
 156 EXPORT_SYMBOL_GPL(rcu_idle_exit);
 157
 158 /*
 159  * Enter an interrupt handler, moving away from idle.
 160  */
 161 void rcu_irq_enter(void)
 162 {
 163         unsigned long flags;
 164         long long oldval;
 165
 166         local_irq_save(flags);
 167         oldval = rcu_dynticks_nesting;
 168         rcu_dynticks_nesting++;
 169         WARN_ON_ONCE(rcu_dynticks_nesting == 0);
 170         rcu_idle_exit_common(oldval);
 171         local_irq_restore(flags);
 172 }
 173 EXPORT_SYMBOL_GPL(rcu_irq_enter);
 174
 175 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
 176
 177 /*
 178  * Test whether RCU thinks that the current CPU is idle.
 179  */
 180 bool notrace __rcu_is_watching(void)
 181 {
 182         return rcu_dynticks_nesting;
 183 }
 184 EXPORT_SYMBOL(__rcu_is_watching);
 185
 186 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
 187
 188 /*
 189  * Test whether the current CPU was interrupted from idle.  Nested
 190  * interrupts don't count, we must be running at the first interrupt
 191  * level.
 192  */
 193 static int rcu_is_cpu_rrupt_from_idle(void)
 194 {
 195         return rcu_dynticks_nesting <= 1;
 196 }
 197
 198 /*
 199  * Helper function for rcu_sched_qs() and rcu_bh_qs().
 200  * Also irqs are disabled to avoid confusion due to interrupt handlers
 201  * invoking call_rcu().
 202  */
 203 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 204 {
 205         RCU_TRACE(reset_cpu_stall_ticks(rcp));
 206         if (rcp->rcucblist != NULL &&
 207             rcp->donetail != rcp->curtail) {
 208                 rcp->donetail = rcp->curtail;
 209                 return 1;
 210         }
 211
 212         return 0;
 213 }
 214
 215 /*
 216  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 217  * are at it, given that any rcu quiescent state is also an rcu_bh
 218  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 219  */
 220 void rcu_sched_qs(void)
 221 {
 222         unsigned long flags;
 223
 224         local_irq_save(flags);
 225         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 226             rcu_qsctr_help(&rcu_bh_ctrlblk))
 227                 raise_softirq(RCU_SOFTIRQ);
 228         local_irq_restore(flags);
 229 }
 230
 231 /*
 232  * Record an rcu_bh quiescent state.
 233  */
 234 void rcu_bh_qs(void)
 235 {
 236         unsigned long flags;
 237
 238         local_irq_save(flags);
 239         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 240                 raise_softirq(RCU_SOFTIRQ);
 241         local_irq_restore(flags);
 242 }
 243
 244 /*
 245  * Check to see if the scheduling-clock interrupt came from an extended
 246  * quiescent state, and, if so, tell RCU about it.  This function must
 247  * be called from hardirq context.  It is normally called from the
 248  * scheduling-clock interrupt.
 249  */
 250 void rcu_check_callbacks(int cpu, int user)
 251 {
 252         RCU_TRACE(check_cpu_stalls());
 253         if (user || rcu_is_cpu_rrupt_from_idle())
 254                 rcu_sched_qs();
 255         else if (!in_softirq())
 256                 rcu_bh_qs();
 257         if (user)
 258                 rcu_note_voluntary_context_switch(current);
 259 }
 260
 261 /*
 262  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 263  * whose grace period has elapsed.
 264  */
 265 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 266 {
 267         const char *rn = NULL;
 268         struct rcu_head *next, *list;
 269         unsigned long flags;
 270         RCU_TRACE(int cb_count = 0);
 271
 272         /* If no RCU callbacks ready to invoke, just return. */
 273         if (&rcp->rcucblist == rcp->donetail) {
 274                 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
 275                 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 276                                               !!ACCESS_ONCE(rcp->rcucblist),
 277                                               need_resched(),
 278                                               is_idle_task(current),
 279                                               false));
 280                 return;
 281         }
 282
 283         /* Move the ready-to-invoke callbacks to a local list. */
 284         local_irq_save(flags);
 285         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 286         list = rcp->rcucblist;
 287         rcp->rcucblist = *rcp->donetail;
 288         *rcp->donetail = NULL;
 289         if (rcp->curtail == rcp->donetail)
 290                 rcp->curtail = &rcp->rcucblist;
 291         rcp->donetail = &rcp->rcucblist;
 292         local_irq_restore(flags);
 293
 294         /* Invoke the callbacks on the local list. */
 295         RCU_TRACE(rn = rcp->name);
 296         while (list) {
 297                 next = list->next;
 298                 prefetch(next);
 299                 debug_rcu_head_unqueue(list);
 300                 local_bh_disable();
 301                 __rcu_reclaim(rn, list);
 302                 local_bh_enable();
 303                 list = next;
 304                 RCU_TRACE(cb_count++);
 305         }
 306         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 307         RCU_TRACE(trace_rcu_batch_end(rcp->name,
 308                                       cb_count, 0, need_resched(),
 309                                       is_idle_task(current),
 310                                       false));
 311 }
 312
 313 static void rcu_process_callbacks(struct softirq_action *unused)
 314 {
 315         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 316         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 317 }
 318
 319 /*
 320  * Wait for a grace period to elapse.  But it is illegal to invoke
 321  * synchronize_sched() from within an RCU read-side critical section.
 322  * Therefore, any legal call to synchronize_sched() is a quiescent
 323  * state, and so on a UP system, synchronize_sched() need do nothing.
 324  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 325  * benefits of doing might_sleep() to reduce latency.)
 326  *
 327  * Cool, huh?  (Due to Josh Triplett.)
 328  *
 329  * But we want to make this a static inline later.  The cond_resched()
 330  * currently makes this problematic.
 331  */
 332 void synchronize_sched(void)
 333 {
 334         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 335                            !lock_is_held(&rcu_lock_map) &&
 336                            !lock_is_held(&rcu_sched_lock_map),
 337                            "Illegal synchronize_sched() in RCU read-side critical section");
 338         cond_resched();
 339 }
 340 EXPORT_SYMBOL_GPL(synchronize_sched);
 341
 342 /*
 343  * Helper function for call_rcu() and call_rcu_bh().
 344  */
 345 static void __call_rcu(struct rcu_head *head,
 346                        void (*func)(struct rcu_head *rcu),
 347                        struct rcu_ctrlblk *rcp)
 348 {
 349         unsigned long flags;
 350
 351         debug_rcu_head_queue(head);
 352         head->func = func;
 353         head->next = NULL;
 354
 355         local_irq_save(flags);
 356         *rcp->curtail = head;
 357         rcp->curtail = &head->next;
 358         RCU_TRACE(rcp->qlen++);
 359         local_irq_restore(flags);
 360 }
 361
 362 /*
 363  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 364  * period.  But since we have but one CPU, that would be after any
 365  * quiescent state.
 366  */
 367 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 368 {
 369         __call_rcu(head, func, &rcu_sched_ctrlblk);
 370 }
 371 EXPORT_SYMBOL_GPL(call_rcu_sched);
 372
 373 /*
 374  * Post an RCU bottom-half callback to be invoked after any subsequent
 375  * quiescent state.
 376  */
 377 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 378 {
 379         __call_rcu(head, func, &rcu_bh_ctrlblk);
 380 }
 381 EXPORT_SYMBOL_GPL(call_rcu_bh);
 382
 383 void rcu_init(void)
 384 {
 385         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 386 }