2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptable semantics.
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.
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.
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.
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
28 #ifdef CONFIG_TREE_PREEMPT_RCU
30 struct rcu_state rcu_preempt_state
= RCU_STATE_INITIALIZER(rcu_preempt_state
);
31 DEFINE_PER_CPU(struct rcu_data
, rcu_preempt_data
);
34 * Tell them what RCU they are running.
36 static inline void rcu_bootup_announce(void)
39 "Experimental preemptable hierarchical RCU implementation.\n");
43 * Return the number of RCU-preempt batches processed thus far
44 * for debug and statistics.
46 long rcu_batches_completed_preempt(void)
48 return rcu_preempt_state
.completed
;
50 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt
);
53 * Return the number of RCU batches processed thus far for debug & stats.
55 long rcu_batches_completed(void)
57 return rcu_batches_completed_preempt();
59 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
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.
67 static void rcu_preempt_qs_record(int cpu
)
69 struct rcu_data
*rdp
= &per_cpu(rcu_preempt_data
, cpu
);
70 rdp
->passed_quiesc
= 1;
71 rdp
->passed_quiesc_completed
= rdp
->completed
;
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.
80 static void rcu_preempt_qs(int cpu
)
82 struct task_struct
*t
= current
;
87 if (t
->rcu_read_lock_nesting
&&
88 (t
->rcu_read_unlock_special
& RCU_READ_UNLOCK_BLOCKED
) == 0) {
90 /* Possibly blocking in an RCU read-side critical section. */
91 rdp
= rcu_preempt_state
.rda
[cpu
];
93 spin_lock(&rnp
->lock
);
94 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_BLOCKED
;
95 t
->rcu_blocked_cpu
= cpu
;
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
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
);
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.
122 rcu_preempt_qs_record(cpu
);
123 t
->rcu_read_unlock_special
&= ~(RCU_READ_UNLOCK_NEED_QS
|
124 RCU_READ_UNLOCK_GOT_QS
);
128 * Tree-preemptable RCU implementation for rcu_read_lock().
129 * Just increment ->rcu_read_lock_nesting, shared state will be updated
132 void __rcu_read_lock(void)
134 ACCESS_ONCE(current
->rcu_read_lock_nesting
)++;
135 barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
137 EXPORT_SYMBOL_GPL(__rcu_read_lock
);
139 static void rcu_read_unlock_special(struct task_struct
*t
)
144 struct rcu_node
*rnp
;
147 /* NMI handlers cannot block and cannot safely manipulate state. */
151 local_irq_save(flags
);
154 * If RCU core is waiting for this CPU to exit critical section,
155 * let it know that we have done so.
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
;
163 /* Hardware IRQ handlers cannot block. */
165 local_irq_restore(flags
);
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
;
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;
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.
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
);
196 /* Report up the rest of the hierarchy. */
198 spin_unlock_irqrestore(&rnp
->lock
, flags
);
200 spin_lock_irqsave(&rnp
->lock
, flags
);
201 cpu_quiet_msk(mask
, &rcu_preempt_state
, rnp
, flags
);
204 spin_unlock(&rnp
->lock
);
206 local_irq_restore(flags
);
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.
216 void __rcu_read_unlock(void)
218 struct task_struct
*t
= current
;
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
);
225 EXPORT_SYMBOL_GPL(__rcu_read_unlock
);
227 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
230 * Scan the current list of tasks blocked within RCU read-side critical
231 * sections, printing out the tid of each.
233 static void rcu_print_task_stall(struct rcu_node
*rnp
)
236 struct list_head
*lp
;
237 int phase
= rnp
->gpnum
& 0x1;
238 struct task_struct
*t
;
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
);
250 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
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
257 static int rcu_preempted_readers(struct rcu_node
*rnp
)
259 return !list_empty(&rnp
->blocked_tasks
[rnp
->gpnum
& 0x1]);
262 #ifdef CONFIG_HOTPLUG_CPU
265 * Do CPU-offline processing for preemptable RCU.
267 static void rcu_preempt_offline_cpu(int cpu
)
269 __rcu_offline_cpu(cpu
, &rcu_preempt_state
);
272 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
275 * Check for a quiescent state from the current CPU. When a task blocks,
276 * the task is recorded in the corresponding CPU's rcu_node structure,
277 * which is checked elsewhere.
279 * Caller must disable hard irqs.
281 static void rcu_preempt_check_callbacks(int cpu
)
283 struct task_struct
*t
= current
;
285 if (t
->rcu_read_lock_nesting
== 0) {
286 t
->rcu_read_unlock_special
&=
287 ~(RCU_READ_UNLOCK_NEED_QS
| RCU_READ_UNLOCK_GOT_QS
);
288 rcu_preempt_qs_record(cpu
);
291 if (per_cpu(rcu_preempt_data
, cpu
).qs_pending
) {
292 if (t
->rcu_read_unlock_special
& RCU_READ_UNLOCK_GOT_QS
) {
293 rcu_preempt_qs_record(cpu
);
294 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_GOT_QS
;
295 } else if (!(t
->rcu_read_unlock_special
&
296 RCU_READ_UNLOCK_NEED_QS
)) {
297 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_NEED_QS
;
303 * Process callbacks for preemptable RCU.
305 static void rcu_preempt_process_callbacks(void)
307 __rcu_process_callbacks(&rcu_preempt_state
,
308 &__get_cpu_var(rcu_preempt_data
));
312 * Queue a preemptable-RCU callback for invocation after a grace period.
314 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
316 __call_rcu(head
, func
, &rcu_preempt_state
);
318 EXPORT_SYMBOL_GPL(call_rcu
);
321 * Check to see if there is any immediate preemptable-RCU-related work
324 static int rcu_preempt_pending(int cpu
)
326 return __rcu_pending(&rcu_preempt_state
,
327 &per_cpu(rcu_preempt_data
, cpu
));
331 * Does preemptable RCU need the CPU to stay out of dynticks mode?
333 static int rcu_preempt_needs_cpu(int cpu
)
335 return !!per_cpu(rcu_preempt_data
, cpu
).nxtlist
;
339 * Initialize preemptable RCU's per-CPU data.
341 static void __cpuinit
rcu_preempt_init_percpu_data(int cpu
)
343 rcu_init_percpu_data(cpu
, &rcu_preempt_state
, 1);
347 * Check for a task exiting while in a preemptable-RCU read-side
348 * critical section, clean up if so. No need to issue warnings,
349 * as debug_check_no_locks_held() already does this if lockdep
354 struct task_struct
*t
= current
;
356 if (t
->rcu_read_lock_nesting
== 0)
358 t
->rcu_read_lock_nesting
= 1;
362 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
365 * Tell them what RCU they are running.
367 static inline void rcu_bootup_announce(void)
369 printk(KERN_INFO
"Hierarchical RCU implementation.\n");
373 * Return the number of RCU batches processed thus far for debug & stats.
375 long rcu_batches_completed(void)
377 return rcu_batches_completed_sched();
379 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
382 * Because preemptable RCU does not exist, we never have to check for
383 * CPUs being in quiescent states.
385 static void rcu_preempt_qs(int cpu
)
389 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
392 * Because preemptable RCU does not exist, we never have to check for
393 * tasks blocked within RCU read-side critical sections.
395 static void rcu_print_task_stall(struct rcu_node
*rnp
)
399 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
402 * Because preemptable RCU does not exist, there are never any preempted
405 static int rcu_preempted_readers(struct rcu_node
*rnp
)
410 #ifdef CONFIG_HOTPLUG_CPU
413 * Because preemptable RCU does not exist, it never needs CPU-offline
416 static void rcu_preempt_offline_cpu(int cpu
)
420 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
423 * Because preemptable RCU does not exist, it never has any callbacks
426 void rcu_preempt_check_callbacks(int cpu
)
431 * Because preemptable RCU does not exist, it never has any callbacks
434 void rcu_preempt_process_callbacks(void)
439 * In classic RCU, call_rcu() is just call_rcu_sched().
441 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
443 call_rcu_sched(head
, func
);
445 EXPORT_SYMBOL_GPL(call_rcu
);
448 * Because preemptable RCU does not exist, it never has any work to do.
450 static int rcu_preempt_pending(int cpu
)
456 * Because preemptable RCU does not exist, it never needs any CPU.
458 static int rcu_preempt_needs_cpu(int cpu
)
464 * Because preemptable RCU does not exist, there is no per-CPU
465 * data to initialize.
467 static void __cpuinit
rcu_preempt_init_percpu_data(int cpu
)
471 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */