6 #include <linux/percpu-refcount.h>
10  * don't try to detect the ref hitting 0 - which means that get/put can just
12  * particular cpu can (and will) wrap - this is fine, when we go to shutdown the
21  * the ref hitting 0 on every put - this would require global synchronization
26  * convert to non percpu mode before the initial ref is dropped everything
29  * Converting to non percpu mode is done with some RCUish stuff in
34 #define PERCPU_COUNT_BIAS	(1LU << (BITS_PER_LONG - 1))
42 		(ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);  in percpu_count_ptr()
46  * percpu_ref_init - initialize a percpu refcount
52  * Initializes @ref.  If @flags is zero, @ref starts in percpu mode with a
56  * Note that @release must not sleep - it may potentially be called from RCU
66 	ref->percpu_count_ptr = (unsigned long)  in percpu_ref_init()
68 	if (!ref->percpu_count_ptr)  in percpu_ref_init()
69 		return -ENOMEM;  in percpu_ref_init()
71 	ref->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;  in percpu_ref_init()
74 		ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;  in percpu_ref_init()
79 		ref->percpu_count_ptr |= __PERCPU_REF_DEAD;  in percpu_ref_init()
83 	atomic_long_set(&ref->count, start_count);  in percpu_ref_init()
85 	ref->release = release;  in percpu_ref_init()
86 	ref->confirm_switch = NULL;  in percpu_ref_init()
92  * percpu_ref_exit - undo percpu_ref_init()
97  * function from are the @ref->release() callback or in init failure path
106 		/* non-NULL confirm_switch indicates switching in progress */  in percpu_ref_exit()
107 		WARN_ON_ONCE(ref->confirm_switch);  in percpu_ref_exit()
109 		ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;  in percpu_ref_exit()
118 	ref->confirm_switch(ref);  in percpu_ref_call_confirm_rcu()
119 	ref->confirm_switch = NULL;  in percpu_ref_call_confirm_rcu()
137 		 atomic_long_read(&ref->count), (long)count);  in percpu_ref_switch_to_atomic_rcu()
141 	 * to &ref->count; since gets could be happening on one cpu while puts  in percpu_ref_switch_to_atomic_rcu()
143 	 * @ref->count to hit 0 before we've got a consistent value - but the  in percpu_ref_switch_to_atomic_rcu()
147 	 * &ref->count; we need the bias value to prevent &ref->count from  in percpu_ref_switch_to_atomic_rcu()
151 	atomic_long_add((long)count - PERCPU_COUNT_BIAS, &ref->count);  in percpu_ref_switch_to_atomic_rcu()
153 	WARN_ONCE(atomic_long_read(&ref->count) <= 0,  in percpu_ref_switch_to_atomic_rcu()
155 		  ref->release, atomic_long_read(&ref->count));  in percpu_ref_switch_to_atomic_rcu()
157 	/* @ref is viewed as dead on all CPUs, send out switch confirmation */  in percpu_ref_switch_to_atomic_rcu()
168 	if (ref->percpu_count_ptr & __PERCPU_REF_ATOMIC) {  in __percpu_ref_switch_to_atomic()
175 	ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;  in __percpu_ref_switch_to_atomic()
178 	 * Non-NULL ->confirm_switch is used to indicate that switching is  in __percpu_ref_switch_to_atomic()
181 	ref->confirm_switch = confirm_switch ?: percpu_ref_noop_confirm_switch;  in __percpu_ref_switch_to_atomic()
184 	call_rcu_sched(&ref->rcu, percpu_ref_switch_to_atomic_rcu);  in __percpu_ref_switch_to_atomic()
194 	if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))  in __percpu_ref_switch_to_percpu()
197 	atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);  in __percpu_ref_switch_to_percpu()
200 	 * Restore per-cpu operation.  smp_store_release() is paired  in __percpu_ref_switch_to_percpu()
208 	smp_store_release(&ref->percpu_count_ptr,  in __percpu_ref_switch_to_percpu()
209 			  ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);  in __percpu_ref_switch_to_percpu()
222 	wait_event_lock_irq(percpu_ref_switch_waitq, !ref->confirm_switch,  in __percpu_ref_switch_mode()
225 	if (ref->force_atomic || (ref->percpu_count_ptr & __PERCPU_REF_DEAD))  in __percpu_ref_switch_mode()
232  * percpu_ref_switch_to_atomic - switch a percpu_ref to atomic mode
233  * @ref: percpu_ref to switch to atomic mode
239  * Schedule switching of @ref to atomic mode.  All its percpu counts will
241  * are guaraneed to be in atomic mode, @confirm_switch, which may not
244  * operations.  Note that @ref will stay in atomic mode across kill/reinit
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.
258 	ref->force_atomic = true;  in percpu_ref_switch_to_atomic()
266  * percpu_ref_switch_to_atomic_sync - switch a percpu_ref to atomic mode
267  * @ref: percpu_ref to switch to atomic mode
269  * Schedule switching the ref to atomic mode, and wait for the
270  * switch to complete.  Caller must ensure that no other thread
271  * will switch back to percpu mode.
276 	wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);  in percpu_ref_switch_to_atomic_sync()
281  * percpu_ref_switch_to_percpu - switch a percpu_ref to percpu mode
282  * @ref: percpu_ref to switch to percpu mode
285  * To re-use an expired ref, use percpu_ref_reinit().
287  * Switch @ref to percpu mode.  This function may be invoked concurrently
295  * mode.  If the caller ensures that @ref is not in the process of
296  * switching to atomic mode, this function can be called from any context.
304 	ref->force_atomic = false;  in percpu_ref_switch_to_percpu()
312  * percpu_ref_kill_and_confirm - drop the initial ref and schedule confirmation
324  * process of switching to atomic mode by percpu_ref_switch_to_atomic().
335 	WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,  in percpu_ref_kill_and_confirm()
336 		  "%s called more than once on %pf!", __func__, ref->release);  in percpu_ref_kill_and_confirm()
338 	ref->percpu_count_ptr |= __PERCPU_REF_DEAD;  in percpu_ref_kill_and_confirm()
347  * percpu_ref_reinit - re-initialize a percpu refcount
348  * @ref: perpcu_ref to re-initialize
350  * Re-initialize @ref so that it's in the same state as when it finished
365 	ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD;  in percpu_ref_reinit()