Pileus Git - ~andy/linux/blob - kernel/rcutree_plugin.h

   1 /*
   2  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
   3  * Internal non-public definitions that provide either classic
   4  * or preemptable semantics.
   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
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  19  *
  20  * Copyright Red Hat, 2009
  21  * Copyright IBM Corporation, 2009
  22  *
  23  * Author: Ingo Molnar <mingo@elte.hu>
  24  *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  25  */
  26
  27
  28 #ifdef CONFIG_TREE_PREEMPT_RCU
  29
  30 struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
  31 DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
  32
  33 /*
  34  * Tell them what RCU they are running.
  35  */
  36 static inline void rcu_bootup_announce(void)
  37 {
  38         printk(KERN_INFO
  39                "Experimental preemptable hierarchical RCU implementation.\n");
  40 }
  41
  42 /*
  43  * Return the number of RCU-preempt batches processed thus far
  44  * for debug and statistics.
  45  */
  46 long rcu_batches_completed_preempt(void)
  47 {
  48         return rcu_preempt_state.completed;
  49 }
  50 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
  51
  52 /*
  53  * Return the number of RCU batches processed thus far for debug & stats.
  54  */
  55 long rcu_batches_completed(void)
  56 {
  57         return rcu_batches_completed_preempt();
  58 }
  59 EXPORT_SYMBOL_GPL(rcu_batches_completed);
  60
  61 /*
  62  * Record a preemptable-RCU quiescent state for the specified CPU.  Note
  63  * that this just means that the task currently running on the CPU is
  64  * not in a quiescent state.  There might be any number of tasks blocked
  65  * while in an RCU read-side critical section.
  66  */
  67 static void rcu_preempt_qs_record(int cpu)
  68 {
  69         struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
  70         rdp->passed_quiesc = 1;
  71         rdp->passed_quiesc_completed = rdp->completed;
  72 }
  73
  74 /*
  75  * We have entered the scheduler or are between softirqs in ksoftirqd.
  76  * If we are in an RCU read-side critical section, we need to reflect
  77  * that in the state of the rcu_node structure corresponding to this CPU.
  78  * Caller must disable hardirqs.
  79  */
  80 static void rcu_preempt_qs(int cpu)
  81 {
  82         struct task_struct *t = current;
  83         int phase;
  84         struct rcu_data *rdp;
  85         struct rcu_node *rnp;
  86
  87         if (t->rcu_read_lock_nesting &&
  88             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
  89
  90                 /* Possibly blocking in an RCU read-side critical section. */
  91                 rdp = rcu_preempt_state.rda[cpu];
  92                 rnp = rdp->mynode;
  93                 spin_lock(&rnp->lock);
  94                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
  95                 t->rcu_blocked_cpu = cpu;
  96
  97                 /*
  98                  * If this CPU has already checked in, then this task
  99                  * will hold up the next grace period rather than the
 100                  * current grace period.  Queue the task accordingly.
 101                  * If the task is queued for the current grace period
 102                  * (i.e., this CPU has not yet passed through a quiescent
 103                  * state for the current grace period), then as long
 104                  * as that task remains queued, the current grace period
 105                  * cannot end.
 106                  */
 107                 phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1);
 108                 list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
 109                 smp_mb();  /* Ensure later ctxt swtch seen after above. */
 110                 spin_unlock(&rnp->lock);
 111         }
 112
 113         /*
 114          * Either we were not in an RCU read-side critical section to
 115          * begin with, or we have now recorded that critical section
 116          * globally.  Either way, we can now note a quiescent state
 117          * for this CPU.  Again, if we were in an RCU read-side critical
 118          * section, and if that critical section was blocking the current
 119          * grace period, then the fact that the task has been enqueued
 120          * means that we continue to block the current grace period.
 121          */
 122         rcu_preempt_qs_record(cpu);
 123         t->rcu_read_unlock_special &= ~(RCU_READ_UNLOCK_NEED_QS |
 124                                         RCU_READ_UNLOCK_GOT_QS);
 125 }
 126
 127 /*
 128  * Tree-preemptable RCU implementation for rcu_read_lock().
 129  * Just increment ->rcu_read_lock_nesting, shared state will be updated
 130  * if we block.
 131  */
 132 void __rcu_read_lock(void)
 133 {
 134         ACCESS_ONCE(current->rcu_read_lock_nesting)++;
 135         barrier();  /* needed if we ever invoke rcu_read_lock in rcutree.c */
 136 }
 137 EXPORT_SYMBOL_GPL(__rcu_read_lock);
 138
 139 static void rcu_read_unlock_special(struct task_struct *t)
 140 {
 141         int empty;
 142         unsigned long flags;
 143         unsigned long mask;
 144         struct rcu_node *rnp;
 145         int special;
 146
 147         /* NMI handlers cannot block and cannot safely manipulate state. */
 148         if (in_nmi())
 149                 return;
 150
 151         local_irq_save(flags);
 152
 153         /*
 154          * If RCU core is waiting for this CPU to exit critical section,
 155          * let it know that we have done so.
 156          */
 157         special = t->rcu_read_unlock_special;
 158         if (special & RCU_READ_UNLOCK_NEED_QS) {
 159                 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
 160                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_GOT_QS;
 161         }
 162
 163         /* Hardware IRQ handlers cannot block. */
 164         if (in_irq()) {
 165                 local_irq_restore(flags);
 166                 return;
 167         }
 168
 169         /* Clean up if blocked during RCU read-side critical section. */
 170         if (special & RCU_READ_UNLOCK_BLOCKED) {
 171                 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
 172
 173                 /* Remove this task from the list it blocked on. */
 174                 rnp = rcu_preempt_state.rda[t->rcu_blocked_cpu]->mynode;
 175                 spin_lock(&rnp->lock);
 176                 empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
 177                 list_del_init(&t->rcu_node_entry);
 178                 t->rcu_blocked_cpu = -1;
 179
 180                 /*
 181                  * If this was the last task on the current list, and if
 182                  * we aren't waiting on any CPUs, report the quiescent state.
 183                  * Note that both cpu_quiet_msk_finish() and cpu_quiet_msk()
 184                  * drop rnp->lock and restore irq.
 185                  */
 186                 if (!empty && rnp->qsmask == 0 &&
 187                     list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])) {
 188                         t->rcu_read_unlock_special &=
 189                                 ~(RCU_READ_UNLOCK_NEED_QS |
 190                                   RCU_READ_UNLOCK_GOT_QS);
 191                         if (rnp->parent == NULL) {
 192                                 /* Only one rcu_node in the tree. */
 193                                 cpu_quiet_msk_finish(&rcu_preempt_state, flags);
 194                                 return;
 195                         }
 196                         /* Report up the rest of the hierarchy. */
 197                         mask = rnp->grpmask;
 198                         spin_unlock_irqrestore(&rnp->lock, flags);
 199                         rnp = rnp->parent;
 200                         spin_lock_irqsave(&rnp->lock, flags);
 201                         cpu_quiet_msk(mask, &rcu_preempt_state, rnp, flags);
 202                         return;
 203                 }
 204                 spin_unlock(&rnp->lock);
 205         }
 206         local_irq_restore(flags);
 207 }
 208
 209 /*
 210  * Tree-preemptable RCU implementation for rcu_read_unlock().
 211  * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
 212  * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
 213  * invoke rcu_read_unlock_special() to clean up after a context switch
 214  * in an RCU read-side critical section and other special cases.
 215  */
 216 void __rcu_read_unlock(void)
 217 {
 218         struct task_struct *t = current;
 219
 220         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
 221         if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
 222             unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 223                 rcu_read_unlock_special(t);
 224 }
 225 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 226
 227 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
 228
 229 /*
 230  * Scan the current list of tasks blocked within RCU read-side critical
 231  * sections, printing out the tid of each.
 232  */
 233 static void rcu_print_task_stall(struct rcu_node *rnp)
 234 {
 235         unsigned long flags;
 236         struct list_head *lp;
 237         int phase = rnp->gpnum & 0x1;
 238         struct task_struct *t;
 239
 240         if (!list_empty(&rnp->blocked_tasks[phase])) {
 241                 spin_lock_irqsave(&rnp->lock, flags);
 242                 phase = rnp->gpnum & 0x1; /* re-read under lock. */
 243                 lp = &rnp->blocked_tasks[phase];
 244                 list_for_each_entry(t, lp, rcu_node_entry)
 245                         printk(" P%d", t->pid);
 246                 spin_unlock_irqrestore(&rnp->lock, flags);
 247         }
 248 }
 249
 250 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 251
 252 /*
 253  * Check for preempted RCU readers for the specified rcu_node structure.
 254  * If the caller needs a reliable answer, it must hold the rcu_node's
 255  * >lock.
 256  */
 257 static int rcu_preempted_readers(struct rcu_node *rnp)
 258 {
 259         return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
 260 }
 261
 262 /*
 263  * Check for a quiescent state from the current CPU.  When a task blocks,
 264  * the task is recorded in the corresponding CPU's rcu_node structure,
 265  * which is checked elsewhere.
 266  *
 267  * Caller must disable hard irqs.
 268  */
 269 static void rcu_preempt_check_callbacks(int cpu)
 270 {
 271         struct task_struct *t = current;
 272
 273         if (t->rcu_read_lock_nesting == 0) {
 274                 t->rcu_read_unlock_special &=
 275                         ~(RCU_READ_UNLOCK_NEED_QS | RCU_READ_UNLOCK_GOT_QS);
 276                 rcu_preempt_qs_record(cpu);
 277                 return;
 278         }
 279         if (per_cpu(rcu_preempt_data, cpu).qs_pending) {
 280                 if (t->rcu_read_unlock_special & RCU_READ_UNLOCK_GOT_QS) {
 281                         rcu_preempt_qs_record(cpu);
 282                         t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_GOT_QS;
 283                 } else if (!(t->rcu_read_unlock_special &
 284                              RCU_READ_UNLOCK_NEED_QS)) {
 285                         t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 286                 }
 287         }
 288 }
 289
 290 /*
 291  * Process callbacks for preemptable RCU.
 292  */
 293 static void rcu_preempt_process_callbacks(void)
 294 {
 295         __rcu_process_callbacks(&rcu_preempt_state,
 296                                 &__get_cpu_var(rcu_preempt_data));
 297 }
 298
 299 /*
 300  * Queue a preemptable-RCU callback for invocation after a grace period.
 301  */
 302 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 303 {
 304         __call_rcu(head, func, &rcu_preempt_state);
 305 }
 306 EXPORT_SYMBOL_GPL(call_rcu);
 307
 308 /*
 309  * Check to see if there is any immediate preemptable-RCU-related work
 310  * to be done.
 311  */
 312 static int rcu_preempt_pending(int cpu)
 313 {
 314         return __rcu_pending(&rcu_preempt_state,
 315                              &per_cpu(rcu_preempt_data, cpu));
 316 }
 317
 318 /*
 319  * Does preemptable RCU need the CPU to stay out of dynticks mode?
 320  */
 321 static int rcu_preempt_needs_cpu(int cpu)
 322 {
 323         return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
 324 }
 325
 326 /*
 327  * Initialize preemptable RCU's per-CPU data.
 328  */
 329 static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
 330 {
 331         rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
 332 }
 333
 334 /*
 335  * Check for a task exiting while in a preemptable-RCU read-side
 336  * critical section, clean up if so.  No need to issue warnings,
 337  * as debug_check_no_locks_held() already does this if lockdep
 338  * is enabled.
 339  */
 340 void exit_rcu(void)
 341 {
 342         struct task_struct *t = current;
 343
 344         if (t->rcu_read_lock_nesting == 0)
 345                 return;
 346         t->rcu_read_lock_nesting = 1;
 347         rcu_read_unlock();
 348 }
 349
 350 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 351
 352 /*
 353  * Tell them what RCU they are running.
 354  */
 355 static inline void rcu_bootup_announce(void)
 356 {
 357         printk(KERN_INFO "Hierarchical RCU implementation.\n");
 358 }
 359
 360 /*
 361  * Return the number of RCU batches processed thus far for debug & stats.
 362  */
 363 long rcu_batches_completed(void)
 364 {
 365         return rcu_batches_completed_sched();
 366 }
 367 EXPORT_SYMBOL_GPL(rcu_batches_completed);
 368
 369 /*
 370  * Because preemptable RCU does not exist, we never have to check for
 371  * CPUs being in quiescent states.
 372  */
 373 static void rcu_preempt_qs(int cpu)
 374 {
 375 }
 376
 377 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
 378
 379 /*
 380  * Because preemptable RCU does not exist, we never have to check for
 381  * tasks blocked within RCU read-side critical sections.
 382  */
 383 static void rcu_print_task_stall(struct rcu_node *rnp)
 384 {
 385 }
 386
 387 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 388
 389 /*
 390  * Because preemptable RCU does not exist, there are never any preempted
 391  * RCU readers.
 392  */
 393 static int rcu_preempted_readers(struct rcu_node *rnp)
 394 {
 395         return 0;
 396 }
 397
 398 /*
 399  * Because preemptable RCU does not exist, it never has any callbacks
 400  * to check.
 401  */
 402 void rcu_preempt_check_callbacks(int cpu)
 403 {
 404 }
 405
 406 /*
 407  * Because preemptable RCU does not exist, it never has any callbacks
 408  * to process.
 409  */
 410 void rcu_preempt_process_callbacks(void)
 411 {
 412 }
 413
 414 /*
 415  * In classic RCU, call_rcu() is just call_rcu_sched().
 416  */
 417 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 418 {
 419         call_rcu_sched(head, func);
 420 }
 421 EXPORT_SYMBOL_GPL(call_rcu);
 422
 423 /*
 424  * Because preemptable RCU does not exist, it never has any work to do.
 425  */
 426 static int rcu_preempt_pending(int cpu)
 427 {
 428         return 0;
 429 }
 430
 431 /*
 432  * Because preemptable RCU does not exist, it never needs any CPU.
 433  */
 434 static int rcu_preempt_needs_cpu(int cpu)
 435 {
 436         return 0;
 437 }
 438
 439 /*
 440  * Because preemptable RCU does not exist, there is no per-CPU
 441  * data to initialize.
 442  */
 443 static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
 444 {
 445 }
 446
 447 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */