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1#define pr_fmt(fmt) "%s: " fmt "\n", __func__
2
3#include <linux/kernel.h>
4#include <linux/sched.h>
5#include <linux/wait.h>
6#include <linux/percpu-refcount.h>
7
8/*
9 * Initially, a percpu refcount is just a set of percpu counters. Initially, we
10 * don't try to detect the ref hitting 0 - which means that get/put can just
11 * increment or decrement the local counter. Note that the counter on a
12 * particular cpu can (and will) wrap - this is fine, when we go to shutdown the
13 * percpu counters will all sum to the correct value
14 *
15 * (More precisely: because modular arithmetic is commutative the sum of all the
16 * percpu_count vars will be equal to what it would have been if all the gets
17 * and puts were done to a single integer, even if some of the percpu integers
18 * overflow or underflow).
19 *
20 * The real trick to implementing percpu refcounts is shutdown. We can't detect
21 * the ref hitting 0 on every put - this would require global synchronization
22 * and defeat the whole purpose of using percpu refs.
23 *
24 * What we do is require the user to keep track of the initial refcount; we know
25 * the ref can't hit 0 before the user drops the initial ref, so as long as we
26 * convert to non percpu mode before the initial ref is dropped everything
27 * works.
28 *
29 * Converting to non percpu mode is done with some RCUish stuff in
30 * percpu_ref_kill. Additionally, we need a bias value so that the
31 * atomic_long_t can't hit 0 before we've added up all the percpu refs.
32 */
33
34#define PERCPU_COUNT_BIAS (1LU << (BITS_PER_LONG - 1))
35
36static DEFINE_SPINLOCK(percpu_ref_switch_lock);
37static DECLARE_WAIT_QUEUE_HEAD(percpu_ref_switch_waitq);
38
39static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
40{
41 return (unsigned long __percpu *)
42 (ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);
43}
44
45/**
46 * percpu_ref_init - initialize a percpu refcount
47 * @ref: percpu_ref to initialize
48 * @release: function which will be called when refcount hits 0
49 * @flags: PERCPU_REF_INIT_* flags
50 * @gfp: allocation mask to use
51 *
52 * Initializes @ref. If @flags is zero, @ref starts in percpu mode with a
53 * refcount of 1; analagous to atomic_long_set(ref, 1). See the
54 * definitions of PERCPU_REF_INIT_* flags for flag behaviors.
55 *
56 * Note that @release must not sleep - it may potentially be called from RCU
57 * callback context by percpu_ref_kill().
58 */
59int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
60 unsigned int flags, gfp_t gfp)
61{
62 size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
63 __alignof__(unsigned long));
64 unsigned long start_count = 0;
65
66 ref->percpu_count_ptr = (unsigned long)
67 __alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
68 if (!ref->percpu_count_ptr)
69 return -ENOMEM;
70
71 ref->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
72
73 if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD))
74 ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
75 else
76 start_count += PERCPU_COUNT_BIAS;
77
78 if (flags & PERCPU_REF_INIT_DEAD)
79 ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
80 else
81 start_count++;
82
83 atomic_long_set(&ref->count, start_count);
84
85 ref->release = release;
86 ref->confirm_switch = NULL;
87 return 0;
88}
89EXPORT_SYMBOL_GPL(percpu_ref_init);
90
91/**
92 * percpu_ref_exit - undo percpu_ref_init()
93 * @ref: percpu_ref to exit
94 *
95 * This function exits @ref. The caller is responsible for ensuring that
96 * @ref is no longer in active use. The usual places to invoke this
97 * function from are the @ref->release() callback or in init failure path
98 * where percpu_ref_init() succeeded but other parts of the initialization
99 * of the embedding object failed.
100 */
101void percpu_ref_exit(struct percpu_ref *ref)
102{
103 unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
104
105 if (percpu_count) {
106 /* non-NULL confirm_switch indicates switching in progress */
107 WARN_ON_ONCE(ref->confirm_switch);
108 free_percpu(percpu_count);
109 ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
110 }
111}
112EXPORT_SYMBOL_GPL(percpu_ref_exit);
113
114static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
115{
116 struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
117
118 ref->confirm_switch(ref);
119 ref->confirm_switch = NULL;
120 wake_up_all(&percpu_ref_switch_waitq);
121
122 /* drop ref from percpu_ref_switch_to_atomic() */
123 percpu_ref_put(ref);
124}
125
126static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
127{
128 struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
129 unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
130 unsigned long count = 0;
131 int cpu;
132
133 for_each_possible_cpu(cpu)
134 count += *per_cpu_ptr(percpu_count, cpu);
135
136 pr_debug("global %ld percpu %ld",
137 atomic_long_read(&ref->count), (long)count);
138
139 /*
140 * It's crucial that we sum the percpu counters _before_ adding the sum
141 * to &ref->count; since gets could be happening on one cpu while puts
142 * happen on another, adding a single cpu's count could cause
143 * @ref->count to hit 0 before we've got a consistent value - but the
144 * sum of all the counts will be consistent and correct.
145 *
146 * Subtracting the bias value then has to happen _after_ adding count to
147 * &ref->count; we need the bias value to prevent &ref->count from
148 * reaching 0 before we add the percpu counts. But doing it at the same
149 * time is equivalent and saves us atomic operations:
150 */
151 atomic_long_add((long)count - PERCPU_COUNT_BIAS, &ref->count);
152
153 WARN_ONCE(atomic_long_read(&ref->count) <= 0,
154 "percpu ref (%pf) <= 0 (%ld) after switching to atomic",
155 ref->release, atomic_long_read(&ref->count));
156
157 /* @ref is viewed as dead on all CPUs, send out switch confirmation */
158 percpu_ref_call_confirm_rcu(rcu);
159}
160
161static void percpu_ref_noop_confirm_switch(struct percpu_ref *ref)
162{
163}
164
165static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,
166 percpu_ref_func_t *confirm_switch)
167{
168 if (ref->percpu_count_ptr & __PERCPU_REF_ATOMIC) {
169 if (confirm_switch)
170 confirm_switch(ref);
171 return;
172 }
173
174 /* switching from percpu to atomic */
175 ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
176
177 /*
178 * Non-NULL ->confirm_switch is used to indicate that switching is
179 * in progress. Use noop one if unspecified.
180 */
181 ref->confirm_switch = confirm_switch ?: percpu_ref_noop_confirm_switch;
182
183 percpu_ref_get(ref); /* put after confirmation */
184 call_rcu_sched(&ref->rcu, percpu_ref_switch_to_atomic_rcu);
185}
186
187static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
188{
189 unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
190 int cpu;
191
192 BUG_ON(!percpu_count);
193
194 if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))
195 return;
196
197 atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);
198
199 /*
200 * Restore per-cpu operation. smp_store_release() is paired with
201 * smp_read_barrier_depends() in __ref_is_percpu() and guarantees
202 * that the zeroing is visible to all percpu accesses which can see
203 * the following __PERCPU_REF_ATOMIC clearing.
204 */
205 for_each_possible_cpu(cpu)
206 *per_cpu_ptr(percpu_count, cpu) = 0;
207
208 smp_store_release(&ref->percpu_count_ptr,
209 ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
210}
211
212static void __percpu_ref_switch_mode(struct percpu_ref *ref,
213 percpu_ref_func_t *confirm_switch)
214{
215 lockdep_assert_held(&percpu_ref_switch_lock);
216
217 /*
218 * If the previous ATOMIC switching hasn't finished yet, wait for
219 * its completion. If the caller ensures that ATOMIC switching
220 * isn't in progress, this function can be called from any context.
221 */
222 wait_event_lock_irq(percpu_ref_switch_waitq, !ref->confirm_switch,
223 percpu_ref_switch_lock);
224
225 if (ref->force_atomic || (ref->percpu_count_ptr & __PERCPU_REF_DEAD))
226 __percpu_ref_switch_to_atomic(ref, confirm_switch);
227 else
228 __percpu_ref_switch_to_percpu(ref);
229}
230
231/**
232 * percpu_ref_switch_to_atomic - switch a percpu_ref to atomic mode
233 * @ref: percpu_ref to switch to atomic mode
234 * @confirm_switch: optional confirmation callback
235 *
236 * There's no reason to use this function for the usual reference counting.
237 * Use percpu_ref_kill[_and_confirm]().
238 *
239 * Schedule switching of @ref to atomic mode. All its percpu counts will
240 * be collected to the main atomic counter. On completion, when all CPUs
241 * are guaraneed to be in atomic mode, @confirm_switch, which may not
242 * block, is invoked. This function may be invoked concurrently with all
243 * the get/put operations and can safely be mixed with kill and reinit
244 * operations. Note that @ref will stay in atomic mode across kill/reinit
245 * cycles until percpu_ref_switch_to_percpu() is called.
246 *
247 * This function may block if @ref is in the process of switching to atomic
248 * mode. If the caller ensures that @ref is not in the process of
249 * switching to atomic mode, this function can be called from any context.
250 */
251void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
252 percpu_ref_func_t *confirm_switch)
253{
254 unsigned long flags;
255
256 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
257
258 ref->force_atomic = true;
259 __percpu_ref_switch_mode(ref, confirm_switch);
260
261 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
262}
263
264/**
265 * percpu_ref_switch_to_percpu - switch a percpu_ref to percpu mode
266 * @ref: percpu_ref to switch to percpu mode
267 *
268 * There's no reason to use this function for the usual reference counting.
269 * To re-use an expired ref, use percpu_ref_reinit().
270 *
271 * Switch @ref to percpu mode. This function may be invoked concurrently
272 * with all the get/put operations and can safely be mixed with kill and
273 * reinit operations. This function reverses the sticky atomic state set
274 * by PERCPU_REF_INIT_ATOMIC or percpu_ref_switch_to_atomic(). If @ref is
275 * dying or dead, the actual switching takes place on the following
276 * percpu_ref_reinit().
277 *
278 * This function may block if @ref is in the process of switching to atomic
279 * mode. If the caller ensures that @ref is not in the process of
280 * switching to atomic mode, this function can be called from any context.
281 */
282void percpu_ref_switch_to_percpu(struct percpu_ref *ref)
283{
284 unsigned long flags;
285
286 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
287
288 ref->force_atomic = false;
289 __percpu_ref_switch_mode(ref, NULL);
290
291 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
292}
293
294/**
295 * percpu_ref_kill_and_confirm - drop the initial ref and schedule confirmation
296 * @ref: percpu_ref to kill
297 * @confirm_kill: optional confirmation callback
298 *
299 * Equivalent to percpu_ref_kill() but also schedules kill confirmation if
300 * @confirm_kill is not NULL. @confirm_kill, which may not block, will be
301 * called after @ref is seen as dead from all CPUs at which point all
302 * further invocations of percpu_ref_tryget_live() will fail. See
303 * percpu_ref_tryget_live() for details.
304 *
305 * This function normally doesn't block and can be called from any context
306 * but it may block if @confirm_kill is specified and @ref is in the
307 * process of switching to atomic mode by percpu_ref_switch_to_atomic().
308 */
309void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
310 percpu_ref_func_t *confirm_kill)
311{
312 unsigned long flags;
313
314 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
315
316 WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,
317 "%s called more than once on %pf!", __func__, ref->release);
318
319 ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
320 __percpu_ref_switch_mode(ref, confirm_kill);
321 percpu_ref_put(ref);
322
323 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
324}
325EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
326
327/**
328 * percpu_ref_reinit - re-initialize a percpu refcount
329 * @ref: perpcu_ref to re-initialize
330 *
331 * Re-initialize @ref so that it's in the same state as when it finished
332 * percpu_ref_init() ignoring %PERCPU_REF_INIT_DEAD. @ref must have been
333 * initialized successfully and reached 0 but not exited.
334 *
335 * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
336 * this function is in progress.
337 */
338void percpu_ref_reinit(struct percpu_ref *ref)
339{
340 unsigned long flags;
341
342 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
343
344 WARN_ON_ONCE(!percpu_ref_is_zero(ref));
345
346 ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD;
347 percpu_ref_get(ref);
348 __percpu_ref_switch_mode(ref, NULL);
349
350 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
351}
352EXPORT_SYMBOL_GPL(percpu_ref_reinit);
1// SPDX-License-Identifier: GPL-2.0-only
2#define pr_fmt(fmt) "%s: " fmt, __func__
3
4#include <linux/kernel.h>
5#include <linux/sched.h>
6#include <linux/wait.h>
7#include <linux/percpu-refcount.h>
8
9/*
10 * Initially, a percpu refcount is just a set of percpu counters. Initially, we
11 * don't try to detect the ref hitting 0 - which means that get/put can just
12 * increment or decrement the local counter. Note that the counter on a
13 * particular cpu can (and will) wrap - this is fine, when we go to shutdown the
14 * percpu counters will all sum to the correct value
15 *
16 * (More precisely: because modular arithmetic is commutative the sum of all the
17 * percpu_count vars will be equal to what it would have been if all the gets
18 * and puts were done to a single integer, even if some of the percpu integers
19 * overflow or underflow).
20 *
21 * The real trick to implementing percpu refcounts is shutdown. We can't detect
22 * the ref hitting 0 on every put - this would require global synchronization
23 * and defeat the whole purpose of using percpu refs.
24 *
25 * What we do is require the user to keep track of the initial refcount; we know
26 * the ref can't hit 0 before the user drops the initial ref, so as long as we
27 * convert to non percpu mode before the initial ref is dropped everything
28 * works.
29 *
30 * Converting to non percpu mode is done with some RCUish stuff in
31 * percpu_ref_kill. Additionally, we need a bias value so that the
32 * atomic_long_t can't hit 0 before we've added up all the percpu refs.
33 */
34
35#define PERCPU_COUNT_BIAS (1LU << (BITS_PER_LONG - 1))
36
37static DEFINE_SPINLOCK(percpu_ref_switch_lock);
38static DECLARE_WAIT_QUEUE_HEAD(percpu_ref_switch_waitq);
39
40static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
41{
42 return (unsigned long __percpu *)
43 (ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);
44}
45
46/**
47 * percpu_ref_init - initialize a percpu refcount
48 * @ref: percpu_ref to initialize
49 * @release: function which will be called when refcount hits 0
50 * @flags: PERCPU_REF_INIT_* flags
51 * @gfp: allocation mask to use
52 *
53 * Initializes @ref. @ref starts out in percpu mode with a refcount of 1 unless
54 * @flags contains PERCPU_REF_INIT_ATOMIC or PERCPU_REF_INIT_DEAD. These flags
55 * change the start state to atomic with the latter setting the initial refcount
56 * to 0. See the definitions of PERCPU_REF_INIT_* flags for flag behaviors.
57 *
58 * Note that @release must not sleep - it may potentially be called from RCU
59 * callback context by percpu_ref_kill().
60 */
61int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
62 unsigned int flags, gfp_t gfp)
63{
64 size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
65 __alignof__(unsigned long));
66 unsigned long start_count = 0;
67
68 ref->percpu_count_ptr = (unsigned long)
69 __alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
70 if (!ref->percpu_count_ptr)
71 return -ENOMEM;
72
73 ref->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
74 ref->allow_reinit = flags & PERCPU_REF_ALLOW_REINIT;
75
76 if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD)) {
77 ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
78 ref->allow_reinit = true;
79 } else {
80 start_count += PERCPU_COUNT_BIAS;
81 }
82
83 if (flags & PERCPU_REF_INIT_DEAD)
84 ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
85 else
86 start_count++;
87
88 atomic_long_set(&ref->count, start_count);
89
90 ref->release = release;
91 ref->confirm_switch = NULL;
92 return 0;
93}
94EXPORT_SYMBOL_GPL(percpu_ref_init);
95
96/**
97 * percpu_ref_exit - undo percpu_ref_init()
98 * @ref: percpu_ref to exit
99 *
100 * This function exits @ref. The caller is responsible for ensuring that
101 * @ref is no longer in active use. The usual places to invoke this
102 * function from are the @ref->release() callback or in init failure path
103 * where percpu_ref_init() succeeded but other parts of the initialization
104 * of the embedding object failed.
105 */
106void percpu_ref_exit(struct percpu_ref *ref)
107{
108 unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
109
110 if (percpu_count) {
111 /* non-NULL confirm_switch indicates switching in progress */
112 WARN_ON_ONCE(ref->confirm_switch);
113 free_percpu(percpu_count);
114 ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
115 }
116}
117EXPORT_SYMBOL_GPL(percpu_ref_exit);
118
119static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
120{
121 struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
122
123 ref->confirm_switch(ref);
124 ref->confirm_switch = NULL;
125 wake_up_all(&percpu_ref_switch_waitq);
126
127 if (!ref->allow_reinit)
128 percpu_ref_exit(ref);
129
130 /* drop ref from percpu_ref_switch_to_atomic() */
131 percpu_ref_put(ref);
132}
133
134static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
135{
136 struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
137 unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
138 unsigned long count = 0;
139 int cpu;
140
141 for_each_possible_cpu(cpu)
142 count += *per_cpu_ptr(percpu_count, cpu);
143
144 pr_debug("global %lu percpu %lu\n",
145 atomic_long_read(&ref->count), count);
146
147 /*
148 * It's crucial that we sum the percpu counters _before_ adding the sum
149 * to &ref->count; since gets could be happening on one cpu while puts
150 * happen on another, adding a single cpu's count could cause
151 * @ref->count to hit 0 before we've got a consistent value - but the
152 * sum of all the counts will be consistent and correct.
153 *
154 * Subtracting the bias value then has to happen _after_ adding count to
155 * &ref->count; we need the bias value to prevent &ref->count from
156 * reaching 0 before we add the percpu counts. But doing it at the same
157 * time is equivalent and saves us atomic operations:
158 */
159 atomic_long_add((long)count - PERCPU_COUNT_BIAS, &ref->count);
160
161 WARN_ONCE(atomic_long_read(&ref->count) <= 0,
162 "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
163 ref->release, atomic_long_read(&ref->count));
164
165 /* @ref is viewed as dead on all CPUs, send out switch confirmation */
166 percpu_ref_call_confirm_rcu(rcu);
167}
168
169static void percpu_ref_noop_confirm_switch(struct percpu_ref *ref)
170{
171}
172
173static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,
174 percpu_ref_func_t *confirm_switch)
175{
176 if (ref->percpu_count_ptr & __PERCPU_REF_ATOMIC) {
177 if (confirm_switch)
178 confirm_switch(ref);
179 return;
180 }
181
182 /* switching from percpu to atomic */
183 ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
184
185 /*
186 * Non-NULL ->confirm_switch is used to indicate that switching is
187 * in progress. Use noop one if unspecified.
188 */
189 ref->confirm_switch = confirm_switch ?: percpu_ref_noop_confirm_switch;
190
191 percpu_ref_get(ref); /* put after confirmation */
192 call_rcu(&ref->rcu, percpu_ref_switch_to_atomic_rcu);
193}
194
195static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
196{
197 unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
198 int cpu;
199
200 BUG_ON(!percpu_count);
201
202 if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))
203 return;
204
205 if (WARN_ON_ONCE(!ref->allow_reinit))
206 return;
207
208 atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);
209
210 /*
211 * Restore per-cpu operation. smp_store_release() is paired
212 * with READ_ONCE() in __ref_is_percpu() and guarantees that the
213 * zeroing is visible to all percpu accesses which can see the
214 * following __PERCPU_REF_ATOMIC clearing.
215 */
216 for_each_possible_cpu(cpu)
217 *per_cpu_ptr(percpu_count, cpu) = 0;
218
219 smp_store_release(&ref->percpu_count_ptr,
220 ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
221}
222
223static void __percpu_ref_switch_mode(struct percpu_ref *ref,
224 percpu_ref_func_t *confirm_switch)
225{
226 lockdep_assert_held(&percpu_ref_switch_lock);
227
228 /*
229 * If the previous ATOMIC switching hasn't finished yet, wait for
230 * its completion. If the caller ensures that ATOMIC switching
231 * isn't in progress, this function can be called from any context.
232 */
233 wait_event_lock_irq(percpu_ref_switch_waitq, !ref->confirm_switch,
234 percpu_ref_switch_lock);
235
236 if (ref->force_atomic || (ref->percpu_count_ptr & __PERCPU_REF_DEAD))
237 __percpu_ref_switch_to_atomic(ref, confirm_switch);
238 else
239 __percpu_ref_switch_to_percpu(ref);
240}
241
242/**
243 * percpu_ref_switch_to_atomic - switch a percpu_ref to atomic mode
244 * @ref: percpu_ref to switch to atomic mode
245 * @confirm_switch: optional confirmation callback
246 *
247 * There's no reason to use this function for the usual reference counting.
248 * Use percpu_ref_kill[_and_confirm]().
249 *
250 * Schedule switching of @ref to atomic mode. All its percpu counts will
251 * be collected to the main atomic counter. On completion, when all CPUs
252 * are guaraneed to be in atomic mode, @confirm_switch, which may not
253 * block, is invoked. This function may be invoked concurrently with all
254 * the get/put operations and can safely be mixed with kill and reinit
255 * operations. Note that @ref will stay in atomic mode across kill/reinit
256 * cycles until percpu_ref_switch_to_percpu() is called.
257 *
258 * This function may block if @ref is in the process of switching to atomic
259 * mode. If the caller ensures that @ref is not in the process of
260 * switching to atomic mode, this function can be called from any context.
261 */
262void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
263 percpu_ref_func_t *confirm_switch)
264{
265 unsigned long flags;
266
267 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
268
269 ref->force_atomic = true;
270 __percpu_ref_switch_mode(ref, confirm_switch);
271
272 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
273}
274EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic);
275
276/**
277 * percpu_ref_switch_to_atomic_sync - switch a percpu_ref to atomic mode
278 * @ref: percpu_ref to switch to atomic mode
279 *
280 * Schedule switching the ref to atomic mode, and wait for the
281 * switch to complete. Caller must ensure that no other thread
282 * will switch back to percpu mode.
283 */
284void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref)
285{
286 percpu_ref_switch_to_atomic(ref, NULL);
287 wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
288}
289EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic_sync);
290
291/**
292 * percpu_ref_switch_to_percpu - switch a percpu_ref to percpu mode
293 * @ref: percpu_ref to switch to percpu mode
294 *
295 * There's no reason to use this function for the usual reference counting.
296 * To re-use an expired ref, use percpu_ref_reinit().
297 *
298 * Switch @ref to percpu mode. This function may be invoked concurrently
299 * with all the get/put operations and can safely be mixed with kill and
300 * reinit operations. This function reverses the sticky atomic state set
301 * by PERCPU_REF_INIT_ATOMIC or percpu_ref_switch_to_atomic(). If @ref is
302 * dying or dead, the actual switching takes place on the following
303 * percpu_ref_reinit().
304 *
305 * This function may block if @ref is in the process of switching to atomic
306 * mode. If the caller ensures that @ref is not in the process of
307 * switching to atomic mode, this function can be called from any context.
308 */
309void percpu_ref_switch_to_percpu(struct percpu_ref *ref)
310{
311 unsigned long flags;
312
313 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
314
315 ref->force_atomic = false;
316 __percpu_ref_switch_mode(ref, NULL);
317
318 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
319}
320EXPORT_SYMBOL_GPL(percpu_ref_switch_to_percpu);
321
322/**
323 * percpu_ref_kill_and_confirm - drop the initial ref and schedule confirmation
324 * @ref: percpu_ref to kill
325 * @confirm_kill: optional confirmation callback
326 *
327 * Equivalent to percpu_ref_kill() but also schedules kill confirmation if
328 * @confirm_kill is not NULL. @confirm_kill, which may not block, will be
329 * called after @ref is seen as dead from all CPUs at which point all
330 * further invocations of percpu_ref_tryget_live() will fail. See
331 * percpu_ref_tryget_live() for details.
332 *
333 * This function normally doesn't block and can be called from any context
334 * but it may block if @confirm_kill is specified and @ref is in the
335 * process of switching to atomic mode by percpu_ref_switch_to_atomic().
336 *
337 * There are no implied RCU grace periods between kill and release.
338 */
339void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
340 percpu_ref_func_t *confirm_kill)
341{
342 unsigned long flags;
343
344 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
345
346 WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,
347 "%s called more than once on %ps!", __func__, ref->release);
348
349 ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
350 __percpu_ref_switch_mode(ref, confirm_kill);
351 percpu_ref_put(ref);
352
353 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
354}
355EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
356
357/**
358 * percpu_ref_reinit - re-initialize a percpu refcount
359 * @ref: perpcu_ref to re-initialize
360 *
361 * Re-initialize @ref so that it's in the same state as when it finished
362 * percpu_ref_init() ignoring %PERCPU_REF_INIT_DEAD. @ref must have been
363 * initialized successfully and reached 0 but not exited.
364 *
365 * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
366 * this function is in progress.
367 */
368void percpu_ref_reinit(struct percpu_ref *ref)
369{
370 WARN_ON_ONCE(!percpu_ref_is_zero(ref));
371
372 percpu_ref_resurrect(ref);
373}
374EXPORT_SYMBOL_GPL(percpu_ref_reinit);
375
376/**
377 * percpu_ref_resurrect - modify a percpu refcount from dead to live
378 * @ref: perpcu_ref to resurrect
379 *
380 * Modify @ref so that it's in the same state as before percpu_ref_kill() was
381 * called. @ref must be dead but must not yet have exited.
382 *
383 * If @ref->release() frees @ref then the caller is responsible for
384 * guaranteeing that @ref->release() does not get called while this
385 * function is in progress.
386 *
387 * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
388 * this function is in progress.
389 */
390void percpu_ref_resurrect(struct percpu_ref *ref)
391{
392 unsigned long __percpu *percpu_count;
393 unsigned long flags;
394
395 spin_lock_irqsave(&percpu_ref_switch_lock, flags);
396
397 WARN_ON_ONCE(!(ref->percpu_count_ptr & __PERCPU_REF_DEAD));
398 WARN_ON_ONCE(__ref_is_percpu(ref, &percpu_count));
399
400 ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD;
401 percpu_ref_get(ref);
402 __percpu_ref_switch_mode(ref, NULL);
403
404 spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
405}
406EXPORT_SYMBOL_GPL(percpu_ref_resurrect);