diff options
Diffstat (limited to 'include/linux/percpu-refcount.h')
| -rw-r--r-- | include/linux/percpu-refcount.h | 308 |
1 files changed, 251 insertions, 57 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index 95961f0bf62d..d73a1c08c3e3 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -1,3 +1,4 @@ +/* SPDX-License-Identifier: GPL-2.0 */ /* * Percpu refcounts: * (C) 2012 Google, Inc. @@ -13,7 +14,7 @@ * * The refcount will have a range of 0 to ((1U << 31) - 1), i.e. one bit less * than an atomic_t - this is because of the way shutdown works, see - * percpu_ref_kill()/PCPU_COUNT_BIAS. + * percpu_ref_kill()/PERCPU_COUNT_BIAS. * * Before you call percpu_ref_kill(), percpu_ref_put() does not check for the * refcount hitting 0 - it can't, if it was in percpu mode. percpu_ref_kill() @@ -29,10 +30,14 @@ * calls io_destroy() or the process exits. * * In the aio code, kill_ioctx() is called when we wish to destroy a kioctx; it - * calls percpu_ref_kill(), then hlist_del_rcu() and sychronize_rcu() to remove - * the kioctx from the proccess's list of kioctxs - after that, there can't be - * any new users of the kioctx (from lookup_ioctx()) and it's then safe to drop - * the initial ref with percpu_ref_put(). + * removes the kioctx from the proccess's table of kioctxs and kills percpu_ref. + * After that, there can't be any new users of the kioctx (from lookup_ioctx()) + * and it's then safe to drop the initial ref with percpu_ref_put(). + * + * Note that the free path, free_ioctx(), needs to go through explicit call_rcu() + * to synchronize with RCU protected lookup_ioctx(). percpu_ref operations don't + * imply RCU grace periods of any kind and if a user wants to combine percpu_ref + * with RCU protection, it must be done explicitly. * * Code that does a two stage shutdown like this often needs some kind of * explicit synchronization to ensure the initial refcount can only be dropped @@ -46,32 +51,86 @@ #define _LINUX_PERCPU_REFCOUNT_H #include <linux/atomic.h> -#include <linux/kernel.h> #include <linux/percpu.h> #include <linux/rcupdate.h> +#include <linux/types.h> +#include <linux/gfp.h> struct percpu_ref; typedef void (percpu_ref_func_t)(struct percpu_ref *); -struct percpu_ref { - atomic_t count; +/* flags set in the lower bits of percpu_ref->percpu_count_ptr */ +enum { + __PERCPU_REF_ATOMIC = 1LU << 0, /* operating in atomic mode */ + __PERCPU_REF_DEAD = 1LU << 1, /* (being) killed */ + __PERCPU_REF_ATOMIC_DEAD = __PERCPU_REF_ATOMIC | __PERCPU_REF_DEAD, + + __PERCPU_REF_FLAG_BITS = 2, +}; + +/* @flags for percpu_ref_init() */ +enum { /* - * The low bit of the pointer indicates whether the ref is in percpu - * mode; if set, then get/put will manipulate the atomic_t (this is a - * hack because we need to keep the pointer around for - * percpu_ref_kill_rcu()) + * Start w/ ref == 1 in atomic mode. Can be switched to percpu + * operation using percpu_ref_switch_to_percpu(). If initialized + * with this flag, the ref will stay in atomic mode until + * percpu_ref_switch_to_percpu() is invoked on it. + * Implies ALLOW_REINIT. */ - unsigned __percpu *pcpu_count; + PERCPU_REF_INIT_ATOMIC = 1 << 0, + + /* + * Start dead w/ ref == 0 in atomic mode. Must be revived with + * percpu_ref_reinit() before used. Implies INIT_ATOMIC and + * ALLOW_REINIT. + */ + PERCPU_REF_INIT_DEAD = 1 << 1, + + /* + * Allow switching from atomic mode to percpu mode. + */ + PERCPU_REF_ALLOW_REINIT = 1 << 2, +}; + +struct percpu_ref_data { + atomic_long_t count; percpu_ref_func_t *release; - percpu_ref_func_t *confirm_kill; + percpu_ref_func_t *confirm_switch; + bool force_atomic:1; + bool allow_reinit:1; struct rcu_head rcu; + struct percpu_ref *ref; +}; + +struct percpu_ref { + /* + * The low bit of the pointer indicates whether the ref is in percpu + * mode; if set, then get/put will manipulate the atomic_t. + */ + unsigned long percpu_count_ptr; + + /* + * 'percpu_ref' is often embedded into user structure, and only + * 'percpu_count_ptr' is required in fast path, move other fields + * into 'percpu_ref_data', so we can reduce memory footprint in + * fast path. + */ + struct percpu_ref_data *data; }; int __must_check percpu_ref_init(struct percpu_ref *ref, - percpu_ref_func_t *release); -void percpu_ref_cancel_init(struct percpu_ref *ref); + percpu_ref_func_t *release, unsigned int flags, + gfp_t gfp); +void percpu_ref_exit(struct percpu_ref *ref); +void percpu_ref_switch_to_atomic(struct percpu_ref *ref, + percpu_ref_func_t *confirm_switch); +void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref); +void percpu_ref_switch_to_percpu(struct percpu_ref *ref); void percpu_ref_kill_and_confirm(struct percpu_ref *ref, percpu_ref_func_t *confirm_kill); +void percpu_ref_resurrect(struct percpu_ref *ref); +void percpu_ref_reinit(struct percpu_ref *ref); +bool percpu_ref_is_zero(struct percpu_ref *ref); /** * percpu_ref_kill - drop the initial ref @@ -80,95 +139,230 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref, * Must be used to drop the initial ref on a percpu refcount; must be called * precisely once before shutdown. * - * Puts @ref in non percpu mode, then does a call_rcu() before gathering up the - * percpu counters and dropping the initial ref. + * Switches @ref into atomic mode before gathering up the percpu counters + * and dropping the initial ref. + * + * There are no implied RCU grace periods between kill and release. */ static inline void percpu_ref_kill(struct percpu_ref *ref) { - return percpu_ref_kill_and_confirm(ref, NULL); + percpu_ref_kill_and_confirm(ref, NULL); +} + +/* + * Internal helper. Don't use outside percpu-refcount proper. The + * function doesn't return the pointer and let the caller test it for NULL + * because doing so forces the compiler to generate two conditional + * branches as it can't assume that @ref->percpu_count is not NULL. + */ +static inline bool __ref_is_percpu(struct percpu_ref *ref, + unsigned long __percpu **percpu_countp) +{ + unsigned long percpu_ptr; + + /* + * The value of @ref->percpu_count_ptr is tested for + * !__PERCPU_REF_ATOMIC, which may be set asynchronously, and then + * used as a pointer. If the compiler generates a separate fetch + * when using it as a pointer, __PERCPU_REF_ATOMIC may be set in + * between contaminating the pointer value, meaning that + * READ_ONCE() is required when fetching it. + * + * The dependency ordering from the READ_ONCE() pairs + * with smp_store_release() in __percpu_ref_switch_to_percpu(). + */ + percpu_ptr = READ_ONCE(ref->percpu_count_ptr); + + /* + * Theoretically, the following could test just ATOMIC; however, + * then we'd have to mask off DEAD separately as DEAD may be + * visible without ATOMIC if we race with percpu_ref_kill(). DEAD + * implies ATOMIC anyway. Test them together. + */ + if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC_DEAD)) + return false; + + *percpu_countp = (unsigned long __percpu *)percpu_ptr; + return true; } -#define PCPU_STATUS_BITS 2 -#define PCPU_STATUS_MASK ((1 << PCPU_STATUS_BITS) - 1) -#define PCPU_REF_PTR 0 -#define PCPU_REF_DEAD 1 +/** + * percpu_ref_get_many - increment a percpu refcount + * @ref: percpu_ref to get + * @nr: number of references to get + * + * Analogous to atomic_long_add(). + * + * This function is safe to call as long as @ref is between init and exit. + */ +static inline void percpu_ref_get_many(struct percpu_ref *ref, unsigned long nr) +{ + unsigned long __percpu *percpu_count; + + rcu_read_lock(); + + if (__ref_is_percpu(ref, &percpu_count)) + this_cpu_add(*percpu_count, nr); + else + atomic_long_add(nr, &ref->data->count); -#define REF_STATUS(count) (((unsigned long) count) & PCPU_STATUS_MASK) + rcu_read_unlock(); +} /** * percpu_ref_get - increment a percpu refcount * @ref: percpu_ref to get * - * Analagous to atomic_inc(). - */ + * Analogous to atomic_long_inc(). + * + * This function is safe to call as long as @ref is between init and exit. + */ static inline void percpu_ref_get(struct percpu_ref *ref) { - unsigned __percpu *pcpu_count; + percpu_ref_get_many(ref, 1); +} - rcu_read_lock_sched(); +/** + * percpu_ref_tryget_many - try to increment a percpu refcount + * @ref: percpu_ref to try-get + * @nr: number of references to get + * + * Increment a percpu refcount by @nr unless its count already reached zero. + * Returns %true on success; %false on failure. + * + * This function is safe to call as long as @ref is between init and exit. + */ +static inline bool percpu_ref_tryget_many(struct percpu_ref *ref, + unsigned long nr) +{ + unsigned long __percpu *percpu_count; + bool ret; - pcpu_count = ACCESS_ONCE(ref->pcpu_count); + rcu_read_lock(); - if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) - __this_cpu_inc(*pcpu_count); - else - atomic_inc(&ref->count); + if (__ref_is_percpu(ref, &percpu_count)) { + this_cpu_add(*percpu_count, nr); + ret = true; + } else { + ret = atomic_long_add_unless(&ref->data->count, nr, 0); + } + + rcu_read_unlock(); - rcu_read_unlock_sched(); + return ret; } /** * percpu_ref_tryget - try to increment a percpu refcount * @ref: percpu_ref to try-get * - * Increment a percpu refcount unless it has already been killed. Returns - * %true on success; %false on failure. + * Increment a percpu refcount unless its count already reached zero. + * Returns %true on success; %false on failure. * - * Completion of percpu_ref_kill() in itself doesn't guarantee that tryget - * will fail. For such guarantee, percpu_ref_kill_and_confirm() should be - * used. After the confirm_kill callback is invoked, it's guaranteed that - * no new reference will be given out by percpu_ref_tryget(). + * This function is safe to call as long as @ref is between init and exit. */ static inline bool percpu_ref_tryget(struct percpu_ref *ref) { - unsigned __percpu *pcpu_count; - int ret = false; + return percpu_ref_tryget_many(ref, 1); +} - rcu_read_lock_sched(); +/** + * percpu_ref_tryget_live_rcu - same as percpu_ref_tryget_live() but the + * caller is responsible for taking RCU. + * + * This function is safe to call as long as @ref is between init and exit. + */ +static inline bool percpu_ref_tryget_live_rcu(struct percpu_ref *ref) +{ + unsigned long __percpu *percpu_count; + bool ret = false; - pcpu_count = ACCESS_ONCE(ref->pcpu_count); + WARN_ON_ONCE(!rcu_read_lock_held()); - if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) { - __this_cpu_inc(*pcpu_count); + if (likely(__ref_is_percpu(ref, &percpu_count))) { + this_cpu_inc(*percpu_count); ret = true; + } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) { + ret = atomic_long_inc_not_zero(&ref->data->count); } + return ret; +} - rcu_read_unlock_sched(); +/** + * percpu_ref_tryget_live - try to increment a live percpu refcount + * @ref: percpu_ref to try-get + * + * Increment a percpu refcount unless it has already been killed. Returns + * %true on success; %false on failure. + * + * Completion of percpu_ref_kill() in itself doesn't guarantee that this + * function will fail. For such guarantee, percpu_ref_kill_and_confirm() + * should be used. After the confirm_kill callback is invoked, it's + * guaranteed that no new reference will be given out by + * percpu_ref_tryget_live(). + * + * This function is safe to call as long as @ref is between init and exit. + */ +static inline bool percpu_ref_tryget_live(struct percpu_ref *ref) +{ + bool ret = false; + rcu_read_lock(); + ret = percpu_ref_tryget_live_rcu(ref); + rcu_read_unlock(); return ret; } /** - * percpu_ref_put - decrement a percpu refcount + * percpu_ref_put_many - decrement a percpu refcount * @ref: percpu_ref to put + * @nr: number of references to put * * Decrement the refcount, and if 0, call the release function (which was passed * to percpu_ref_init()) + * + * This function is safe to call as long as @ref is between init and exit. */ -static inline void percpu_ref_put(struct percpu_ref *ref) +static inline void percpu_ref_put_many(struct percpu_ref *ref, unsigned long nr) { - unsigned __percpu *pcpu_count; + unsigned long __percpu *percpu_count; - rcu_read_lock_sched(); + rcu_read_lock(); - pcpu_count = ACCESS_ONCE(ref->pcpu_count); + if (__ref_is_percpu(ref, &percpu_count)) + this_cpu_sub(*percpu_count, nr); + else if (unlikely(atomic_long_sub_and_test(nr, &ref->data->count))) + ref->data->release(ref); - if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) - __this_cpu_dec(*pcpu_count); - else if (unlikely(atomic_dec_and_test(&ref->count))) - ref->release(ref); + rcu_read_unlock(); +} + +/** + * percpu_ref_put - decrement a percpu refcount + * @ref: percpu_ref to put + * + * Decrement the refcount, and if 0, call the release function (which was passed + * to percpu_ref_init()) + * + * This function is safe to call as long as @ref is between init and exit. + */ +static inline void percpu_ref_put(struct percpu_ref *ref) +{ + percpu_ref_put_many(ref, 1); +} - rcu_read_unlock_sched(); +/** + * percpu_ref_is_dying - test whether a percpu refcount is dying or dead + * @ref: percpu_ref to test + * + * Returns %true if @ref is dying or dead. + * + * This function is safe to call as long as @ref is between init and exit + * and the caller is responsible for synchronizing against state changes. + */ +static inline bool percpu_ref_is_dying(struct percpu_ref *ref) +{ + return ref->percpu_count_ptr & __PERCPU_REF_DEAD; } #endif |