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(int cpu
)
69 struct rcu_data
*rdp
= &per_cpu(rcu_preempt_data
, cpu
);
70 rdp
->passed_quiesc_completed
= rdp
->completed
;
72 rdp
->passed_quiesc
= 1;
76 * We have entered the scheduler, and the current task might soon be
77 * context-switched away from. If this task is in an RCU read-side
78 * critical section, we will no longer be able to rely on the CPU to
79 * record that fact, so we enqueue the task on the appropriate entry
80 * of the blocked_tasks[] array. The task will dequeue itself when
81 * it exits the outermost enclosing RCU read-side critical section.
82 * Therefore, the current grace period cannot be permitted to complete
83 * until the blocked_tasks[] entry indexed by the low-order bit of
86 * Caller must disable preemption.
88 static void rcu_preempt_note_context_switch(int cpu
)
90 struct task_struct
*t
= current
;
96 if (t
->rcu_read_lock_nesting
&&
97 (t
->rcu_read_unlock_special
& RCU_READ_UNLOCK_BLOCKED
) == 0) {
99 /* Possibly blocking in an RCU read-side critical section. */
100 rdp
= rcu_preempt_state
.rda
[cpu
];
102 spin_lock_irqsave(&rnp
->lock
, flags
);
103 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_BLOCKED
;
104 t
->rcu_blocked_node
= rnp
;
107 * If this CPU has already checked in, then this task
108 * will hold up the next grace period rather than the
109 * current grace period. Queue the task accordingly.
110 * If the task is queued for the current grace period
111 * (i.e., this CPU has not yet passed through a quiescent
112 * state for the current grace period), then as long
113 * as that task remains queued, the current grace period
116 * But first, note that the current CPU must still be
119 WARN_ON_ONCE((rdp
->grpmask
& rnp
->qsmaskinit
) == 0);
120 phase
= !(rnp
->qsmask
& rdp
->grpmask
) ^ (rnp
->gpnum
& 0x1);
121 list_add(&t
->rcu_node_entry
, &rnp
->blocked_tasks
[phase
]);
122 smp_mb(); /* Ensure later ctxt swtch seen after above. */
123 spin_unlock_irqrestore(&rnp
->lock
, flags
);
127 * Either we were not in an RCU read-side critical section to
128 * begin with, or we have now recorded that critical section
129 * globally. Either way, we can now note a quiescent state
130 * for this CPU. Again, if we were in an RCU read-side critical
131 * section, and if that critical section was blocking the current
132 * grace period, then the fact that the task has been enqueued
133 * means that we continue to block the current grace period.
136 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_NEED_QS
;
140 * Tree-preemptable RCU implementation for rcu_read_lock().
141 * Just increment ->rcu_read_lock_nesting, shared state will be updated
144 void __rcu_read_lock(void)
146 ACCESS_ONCE(current
->rcu_read_lock_nesting
)++;
147 barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
149 EXPORT_SYMBOL_GPL(__rcu_read_lock
);
151 static void rcu_read_unlock_special(struct task_struct
*t
)
156 struct rcu_node
*rnp
;
159 /* NMI handlers cannot block and cannot safely manipulate state. */
163 local_irq_save(flags
);
166 * If RCU core is waiting for this CPU to exit critical section,
167 * let it know that we have done so.
169 special
= t
->rcu_read_unlock_special
;
170 if (special
& RCU_READ_UNLOCK_NEED_QS
) {
171 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_NEED_QS
;
172 rcu_preempt_qs(smp_processor_id());
175 /* Hardware IRQ handlers cannot block. */
177 local_irq_restore(flags
);
181 /* Clean up if blocked during RCU read-side critical section. */
182 if (special
& RCU_READ_UNLOCK_BLOCKED
) {
183 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_BLOCKED
;
186 * Remove this task from the list it blocked on. The
187 * task can migrate while we acquire the lock, but at
188 * most one time. So at most two passes through loop.
191 rnp
= t
->rcu_blocked_node
;
192 spin_lock(&rnp
->lock
);
193 if (rnp
== t
->rcu_blocked_node
)
195 spin_unlock(&rnp
->lock
);
197 empty
= list_empty(&rnp
->blocked_tasks
[rnp
->gpnum
& 0x1]);
198 list_del_init(&t
->rcu_node_entry
);
199 t
->rcu_blocked_node
= NULL
;
202 * If this was the last task on the current list, and if
203 * we aren't waiting on any CPUs, report the quiescent state.
204 * Note that both cpu_quiet_msk_finish() and cpu_quiet_msk()
205 * drop rnp->lock and restore irq.
207 if (!empty
&& rnp
->qsmask
== 0 &&
208 list_empty(&rnp
->blocked_tasks
[rnp
->gpnum
& 0x1])) {
209 struct rcu_node
*rnp_p
;
211 if (rnp
->parent
== NULL
) {
212 /* Only one rcu_node in the tree. */
213 cpu_quiet_msk_finish(&rcu_preempt_state
, flags
);
216 /* Report up the rest of the hierarchy. */
218 spin_unlock_irqrestore(&rnp
->lock
, flags
);
220 spin_lock_irqsave(&rnp_p
->lock
, flags
);
221 WARN_ON_ONCE(rnp
->qsmask
);
222 cpu_quiet_msk(mask
, &rcu_preempt_state
, rnp_p
, flags
);
225 spin_unlock(&rnp
->lock
);
227 local_irq_restore(flags
);
231 * Tree-preemptable RCU implementation for rcu_read_unlock().
232 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
233 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
234 * invoke rcu_read_unlock_special() to clean up after a context switch
235 * in an RCU read-side critical section and other special cases.
237 void __rcu_read_unlock(void)
239 struct task_struct
*t
= current
;
241 barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */
242 if (--ACCESS_ONCE(t
->rcu_read_lock_nesting
) == 0 &&
243 unlikely(ACCESS_ONCE(t
->rcu_read_unlock_special
)))
244 rcu_read_unlock_special(t
);
246 EXPORT_SYMBOL_GPL(__rcu_read_unlock
);
248 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
251 * Scan the current list of tasks blocked within RCU read-side critical
252 * sections, printing out the tid of each.
254 static void rcu_print_task_stall(struct rcu_node
*rnp
)
257 struct list_head
*lp
;
258 int phase
= rnp
->gpnum
& 0x1;
259 struct task_struct
*t
;
261 if (!list_empty(&rnp
->blocked_tasks
[phase
])) {
262 spin_lock_irqsave(&rnp
->lock
, flags
);
263 phase
= rnp
->gpnum
& 0x1; /* re-read under lock. */
264 lp
= &rnp
->blocked_tasks
[phase
];
265 list_for_each_entry(t
, lp
, rcu_node_entry
)
266 printk(" P%d", t
->pid
);
267 spin_unlock_irqrestore(&rnp
->lock
, flags
);
271 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
274 * Check that the list of blocked tasks for the newly completed grace
275 * period is in fact empty. It is a serious bug to complete a grace
276 * period that still has RCU readers blocked! This function must be
277 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
278 * must be held by the caller.
280 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
282 WARN_ON_ONCE(!list_empty(&rnp
->blocked_tasks
[rnp
->gpnum
& 0x1]));
283 WARN_ON_ONCE(rnp
->qsmask
);
287 * Check for preempted RCU readers for the specified rcu_node structure.
288 * If the caller needs a reliable answer, it must hold the rcu_node's
291 static int rcu_preempted_readers(struct rcu_node
*rnp
)
293 return !list_empty(&rnp
->blocked_tasks
[rnp
->gpnum
& 0x1]);
296 #ifdef CONFIG_HOTPLUG_CPU
299 * Handle tasklist migration for case in which all CPUs covered by the
300 * specified rcu_node have gone offline. Move them up to the root
301 * rcu_node. The reason for not just moving them to the immediate
302 * parent is to remove the need for rcu_read_unlock_special() to
303 * make more than two attempts to acquire the target rcu_node's lock.
305 * The caller must hold rnp->lock with irqs disabled.
307 static void rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
308 struct rcu_node
*rnp
,
309 struct rcu_data
*rdp
)
312 struct list_head
*lp
;
313 struct list_head
*lp_root
;
314 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
315 struct task_struct
*tp
;
317 if (rnp
== rnp_root
) {
318 WARN_ONCE(1, "Last CPU thought to be offlined?");
319 return; /* Shouldn't happen: at least one CPU online. */
321 WARN_ON_ONCE(rnp
!= rdp
->mynode
&&
322 (!list_empty(&rnp
->blocked_tasks
[0]) ||
323 !list_empty(&rnp
->blocked_tasks
[1])));
326 * Move tasks up to root rcu_node. Rely on the fact that the
327 * root rcu_node can be at most one ahead of the rest of the
328 * rcu_nodes in terms of gp_num value. This fact allows us to
329 * move the blocked_tasks[] array directly, element by element.
331 for (i
= 0; i
< 2; i
++) {
332 lp
= &rnp
->blocked_tasks
[i
];
333 lp_root
= &rnp_root
->blocked_tasks
[i
];
334 while (!list_empty(lp
)) {
335 tp
= list_entry(lp
->next
, typeof(*tp
), rcu_node_entry
);
336 spin_lock(&rnp_root
->lock
); /* irqs already disabled */
337 list_del(&tp
->rcu_node_entry
);
338 tp
->rcu_blocked_node
= rnp_root
;
339 list_add(&tp
->rcu_node_entry
, lp_root
);
340 spin_unlock(&rnp_root
->lock
); /* irqs remain disabled */
346 * Do CPU-offline processing for preemptable RCU.
348 static void rcu_preempt_offline_cpu(int cpu
)
350 __rcu_offline_cpu(cpu
, &rcu_preempt_state
);
353 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
356 * Check for a quiescent state from the current CPU. When a task blocks,
357 * the task is recorded in the corresponding CPU's rcu_node structure,
358 * which is checked elsewhere.
360 * Caller must disable hard irqs.
362 static void rcu_preempt_check_callbacks(int cpu
)
364 struct task_struct
*t
= current
;
366 if (t
->rcu_read_lock_nesting
== 0) {
367 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_NEED_QS
;
371 if (per_cpu(rcu_preempt_data
, cpu
).qs_pending
) {
372 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_NEED_QS
;
377 * Process callbacks for preemptable RCU.
379 static void rcu_preempt_process_callbacks(void)
381 __rcu_process_callbacks(&rcu_preempt_state
,
382 &__get_cpu_var(rcu_preempt_data
));
386 * Queue a preemptable-RCU callback for invocation after a grace period.
388 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
390 __call_rcu(head
, func
, &rcu_preempt_state
);
392 EXPORT_SYMBOL_GPL(call_rcu
);
395 * Check to see if there is any immediate preemptable-RCU-related work
398 static int rcu_preempt_pending(int cpu
)
400 return __rcu_pending(&rcu_preempt_state
,
401 &per_cpu(rcu_preempt_data
, cpu
));
405 * Does preemptable RCU need the CPU to stay out of dynticks mode?
407 static int rcu_preempt_needs_cpu(int cpu
)
409 return !!per_cpu(rcu_preempt_data
, cpu
).nxtlist
;
413 * Initialize preemptable RCU's per-CPU data.
415 static void __cpuinit
rcu_preempt_init_percpu_data(int cpu
)
417 rcu_init_percpu_data(cpu
, &rcu_preempt_state
, 1);
421 * Check for a task exiting while in a preemptable-RCU read-side
422 * critical section, clean up if so. No need to issue warnings,
423 * as debug_check_no_locks_held() already does this if lockdep
428 struct task_struct
*t
= current
;
430 if (t
->rcu_read_lock_nesting
== 0)
432 t
->rcu_read_lock_nesting
= 1;
436 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
439 * Tell them what RCU they are running.
441 static inline void rcu_bootup_announce(void)
443 printk(KERN_INFO
"Hierarchical RCU implementation.\n");
447 * Return the number of RCU batches processed thus far for debug & stats.
449 long rcu_batches_completed(void)
451 return rcu_batches_completed_sched();
453 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
456 * Because preemptable RCU does not exist, we never have to check for
457 * CPUs being in quiescent states.
459 static void rcu_preempt_note_context_switch(int cpu
)
463 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
466 * Because preemptable RCU does not exist, we never have to check for
467 * tasks blocked within RCU read-side critical sections.
469 static void rcu_print_task_stall(struct rcu_node
*rnp
)
473 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
476 * Because there is no preemptable RCU, there can be no readers blocked,
477 * so there is no need to check for blocked tasks.
479 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
484 * Because preemptable RCU does not exist, there are never any preempted
487 static int rcu_preempted_readers(struct rcu_node
*rnp
)
492 #ifdef CONFIG_HOTPLUG_CPU
495 * Because preemptable RCU does not exist, it never needs to migrate
496 * tasks that were blocked within RCU read-side critical sections.
498 static void rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
499 struct rcu_node
*rnp
,
500 struct rcu_data
*rdp
)
505 * Because preemptable RCU does not exist, it never needs CPU-offline
508 static void rcu_preempt_offline_cpu(int cpu
)
512 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
515 * Because preemptable RCU does not exist, it never has any callbacks
518 void rcu_preempt_check_callbacks(int cpu
)
523 * Because preemptable RCU does not exist, it never has any callbacks
526 void rcu_preempt_process_callbacks(void)
531 * In classic RCU, call_rcu() is just call_rcu_sched().
533 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
535 call_rcu_sched(head
, func
);
537 EXPORT_SYMBOL_GPL(call_rcu
);
540 * Because preemptable RCU does not exist, it never has any work to do.
542 static int rcu_preempt_pending(int cpu
)
548 * Because preemptable RCU does not exist, it never needs any CPU.
550 static int rcu_preempt_needs_cpu(int cpu
)
556 * Because preemptable RCU does not exist, there is no per-CPU
557 * data to initialize.
559 static void __cpuinit
rcu_preempt_init_percpu_data(int cpu
)
563 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */