12  * don't try to detect the ref hitting 0 - which means that get/put can just
23  * the ref hitting 0 on every put - this would require global synchronization
27  * the ref can't hit 0 before the user drops the initial ref, so as long as we
28  * convert to non percpu mode before the initial ref is dropped everything
41 static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)  in percpu_count_ptr()  argument
44 		(ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);  in percpu_count_ptr()
49  * @ref: percpu_ref to initialize
54  * Initializes @ref.  @ref starts out in percpu mode with a refcount of 1 unless
62 int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,  in percpu_ref_init()  argument
70 	ref->percpu_count_ptr = (unsigned long)  in percpu_ref_init()
72 	if (!ref->percpu_count_ptr)  in percpu_ref_init()
75 	data = kzalloc(sizeof(*ref->data), gfp);  in percpu_ref_init()
77 		free_percpu((void __percpu *)ref->percpu_count_ptr);  in percpu_ref_init()
85 		ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;  in percpu_ref_init()
92 		ref->percpu_count_ptr |= __PERCPU_REF_DEAD;  in percpu_ref_init()
100 	data->ref = ref;  in percpu_ref_init()
101 	ref->data = data;  in percpu_ref_init()
106 static void __percpu_ref_exit(struct percpu_ref *ref)  in __percpu_ref_exit()  argument
108 	unsigned long __percpu *percpu_count = percpu_count_ptr(ref);  in __percpu_ref_exit()
112 		WARN_ON_ONCE(ref->data && ref->data->confirm_switch);  in __percpu_ref_exit()
114 		ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;  in __percpu_ref_exit()
120  * @ref: percpu_ref to exit
122  * This function exits @ref.  The caller is responsible for ensuring that
123  * @ref is no longer in active use.  The usual places to invoke this
124  * function from are the @ref->release() callback or in init failure path
128 void percpu_ref_exit(struct percpu_ref *ref)  in percpu_ref_exit()  argument
130 	struct percpu_ref_data *data = ref->data;  in percpu_ref_exit()
133 	__percpu_ref_exit(ref);  in percpu_ref_exit()
139 	ref->percpu_count_ptr |= atomic_long_read(&ref->data->count) <<  in percpu_ref_exit()
141 	ref->data = NULL;  in percpu_ref_exit()
152 	struct percpu_ref *ref = data->ref;  in percpu_ref_call_confirm_rcu()  local
154 	data->confirm_switch(ref);  in percpu_ref_call_confirm_rcu()
159 		__percpu_ref_exit(ref);  in percpu_ref_call_confirm_rcu()
161 	/* drop ref from percpu_ref_switch_to_atomic() */  in percpu_ref_call_confirm_rcu()
162 	percpu_ref_put(ref);  in percpu_ref_call_confirm_rcu()
169 	struct percpu_ref *ref = data->ref;  in percpu_ref_switch_to_atomic_rcu()  local
170 	unsigned long __percpu *percpu_count = percpu_count_ptr(ref);  in percpu_ref_switch_to_atomic_rcu()
182 	 * to &ref->count; since gets could be happening on one cpu while puts  in percpu_ref_switch_to_atomic_rcu()
184 	 * @ref->count to hit 0 before we've got a consistent value - but the  in percpu_ref_switch_to_atomic_rcu()
188 	 * &ref->count; we need the bias value to prevent &ref->count from  in percpu_ref_switch_to_atomic_rcu()
195 		  "percpu ref (%ps) <= 0 (%ld) after switching to atomic",  in percpu_ref_switch_to_atomic_rcu()
198 	/* @ref is viewed as dead on all CPUs, send out switch confirmation */  in percpu_ref_switch_to_atomic_rcu()
202 static void percpu_ref_noop_confirm_switch(struct percpu_ref *ref)  in percpu_ref_noop_confirm_switch()  argument
206 static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,  in __percpu_ref_switch_to_atomic()  argument
209 	if (ref->percpu_count_ptr & __PERCPU_REF_ATOMIC) {  in __percpu_ref_switch_to_atomic()
211 			confirm_switch(ref);  in __percpu_ref_switch_to_atomic()
216 	ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;  in __percpu_ref_switch_to_atomic()
222 	ref->data->confirm_switch = confirm_switch ?:  in __percpu_ref_switch_to_atomic()
225 	percpu_ref_get(ref);	/* put after confirmation */  in __percpu_ref_switch_to_atomic()
226 	call_rcu(&ref->data->rcu, percpu_ref_switch_to_atomic_rcu);  in __percpu_ref_switch_to_atomic()
229 static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)  in __percpu_ref_switch_to_percpu()  argument
231 	unsigned long __percpu *percpu_count = percpu_count_ptr(ref);  in __percpu_ref_switch_to_percpu()
236 	if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))  in __percpu_ref_switch_to_percpu()
239 	if (WARN_ON_ONCE(!ref->data->allow_reinit))  in __percpu_ref_switch_to_percpu()
242 	atomic_long_add(PERCPU_COUNT_BIAS, &ref->data->count);  in __percpu_ref_switch_to_percpu()
253 	smp_store_release(&ref->percpu_count_ptr,  in __percpu_ref_switch_to_percpu()
254 			  ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);  in __percpu_ref_switch_to_percpu()
257 static void __percpu_ref_switch_mode(struct percpu_ref *ref,  in __percpu_ref_switch_mode()  argument
260 	struct percpu_ref_data *data = ref->data;  in __percpu_ref_switch_mode()
272 	if (data->force_atomic || (ref->percpu_count_ptr & __PERCPU_REF_DEAD))  in __percpu_ref_switch_mode()
273 		__percpu_ref_switch_to_atomic(ref, confirm_switch);  in __percpu_ref_switch_mode()
275 		__percpu_ref_switch_to_percpu(ref);  in __percpu_ref_switch_mode()
280  * @ref: percpu_ref to switch to atomic mode
286  * Schedule switching of @ref to atomic mode.  All its percpu counts will
291  * operations.  Note that @ref will stay in atomic mode across kill/reinit
294  * This function may block if @ref is in the process of switching to atomic
295  * mode.  If the caller ensures that @ref is not in the process of
298 void percpu_ref_switch_to_atomic(struct percpu_ref *ref,  in percpu_ref_switch_to_atomic()  argument
305 	ref->data->force_atomic = true;  in percpu_ref_switch_to_atomic()
306 	__percpu_ref_switch_mode(ref, confirm_switch);  in percpu_ref_switch_to_atomic()
314  * @ref: percpu_ref to switch to atomic mode
316  * Schedule switching the ref to atomic mode, and wait for the
320 void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref)  in percpu_ref_switch_to_atomic_sync()  argument
322 	percpu_ref_switch_to_atomic(ref, NULL);  in percpu_ref_switch_to_atomic_sync()
323 	wait_event(percpu_ref_switch_waitq, !ref->data->confirm_switch);  in percpu_ref_switch_to_atomic_sync()
329  * @ref: percpu_ref to switch to percpu mode
332  * To re-use an expired ref, use percpu_ref_reinit().
334  * Switch @ref to percpu mode.  This function may be invoked concurrently
337  * by PERCPU_REF_INIT_ATOMIC or percpu_ref_switch_to_atomic().  If @ref is
341  * This function may block if @ref is in the process of switching to atomic
342  * mode.  If the caller ensures that @ref is not in the process of
345 void percpu_ref_switch_to_percpu(struct percpu_ref *ref)  in percpu_ref_switch_to_percpu()  argument
351 	ref->data->force_atomic = false;  in percpu_ref_switch_to_percpu()
352 	__percpu_ref_switch_mode(ref, NULL);  in percpu_ref_switch_to_percpu()
359  * percpu_ref_kill_and_confirm - drop the initial ref and schedule confirmation
360  * @ref: percpu_ref to kill
365  * called after @ref is seen as dead from all CPUs at which point all
370  * but it may block if @confirm_kill is specified and @ref is in the
375 void percpu_ref_kill_and_confirm(struct percpu_ref *ref,  in percpu_ref_kill_and_confirm()  argument
382 	WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,  in percpu_ref_kill_and_confirm()
384 		  ref->data->release);  in percpu_ref_kill_and_confirm()
386 	ref->percpu_count_ptr |= __PERCPU_REF_DEAD;  in percpu_ref_kill_and_confirm()
387 	__percpu_ref_switch_mode(ref, confirm_kill);  in percpu_ref_kill_and_confirm()
388 	percpu_ref_put(ref);  in percpu_ref_kill_and_confirm()
396  * @ref: percpu_ref to test
398  * Returns %true if @ref reached zero.
400  * This function is safe to call as long as @ref is between init and exit.
402 bool percpu_ref_is_zero(struct percpu_ref *ref)  in percpu_ref_is_zero()  argument
407 	if (__ref_is_percpu(ref, &percpu_count))  in percpu_ref_is_zero()
412 	if (ref->data)  in percpu_ref_is_zero()
413 		count = atomic_long_read(&ref->data->count);  in percpu_ref_is_zero()
415 		count = ref->percpu_count_ptr >> __PERCPU_REF_FLAG_BITS;  in percpu_ref_is_zero()
424  * @ref: perpcu_ref to re-initialize
426  * Re-initialize @ref so that it's in the same state as when it finished
427  * percpu_ref_init() ignoring %PERCPU_REF_INIT_DEAD.  @ref must have been
430  * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
433 void percpu_ref_reinit(struct percpu_ref *ref)  in percpu_ref_reinit()  argument
435 	WARN_ON_ONCE(!percpu_ref_is_zero(ref));  in percpu_ref_reinit()
437 	percpu_ref_resurrect(ref);  in percpu_ref_reinit()
443  * @ref: perpcu_ref to resurrect
445  * Modify @ref so that it's in the same state as before percpu_ref_kill() was
446  * called. @ref must be dead but must not yet have exited.
448  * If @ref->release() frees @ref then the caller is responsible for
449  * guaranteeing that @ref->release() does not get called while this
452  * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
455 void percpu_ref_resurrect(struct percpu_ref *ref)  in percpu_ref_resurrect()  argument
462 	WARN_ON_ONCE(!(ref->percpu_count_ptr & __PERCPU_REF_DEAD));  in percpu_ref_resurrect()
463 	WARN_ON_ONCE(__ref_is_percpu(ref, &percpu_count));  in percpu_ref_resurrect()
465 	ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD;  in percpu_ref_resurrect()
466 	percpu_ref_get(ref);  in percpu_ref_resurrect()
467 	__percpu_ref_switch_mode(ref, NULL);  in percpu_ref_resurrect()