| /* SPDX-License-Identifier: GPL-2.0 */ |
| /* |
| * Percpu refcounts: |
| * (C) 2012 Google, Inc. |
| * Author: Kent Overstreet <koverstreet@google.com> |
| * |
| * This implements a refcount with similar semantics to atomic_t - atomic_inc(), |
| * atomic_dec_and_test() - but percpu. |
| * |
| * There's one important difference between percpu refs and normal atomic_t |
| * refcounts; you have to keep track of your initial refcount, and then when you |
| * start shutting down you call percpu_ref_kill() _before_ dropping the initial |
| * refcount. |
| * |
| * 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()/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() |
| * puts the ref back in single atomic_t mode, collecting the per cpu refs and |
| * issuing the appropriate barriers, and then marks the ref as shutting down so |
| * that percpu_ref_put() will check for the ref hitting 0. After it returns, |
| * it's safe to drop the initial ref. |
| * |
| * USAGE: |
| * |
| * See fs/aio.c for some example usage; it's used there for struct kioctx, which |
| * is created when userspaces calls io_setup(), and destroyed when userspace |
| * calls io_destroy() or the process exits. |
| * |
| * In the aio code, kill_ioctx() is called when we wish to destroy a kioctx; it |
| * 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 |
| * once - percpu_ref_kill() does this for you, it returns true once and false if |
| * someone else already called it. The aio code uses it this way, but it's not |
| * necessary if the code has some other mechanism to synchronize teardown. |
| * around. |
| */ |
| |
| #ifndef _LINUX_PERCPU_REFCOUNT_H |
| #define _LINUX_PERCPU_REFCOUNT_H |
| |
| #include <linux/atomic.h> |
| #include <linux/kernel.h> |
| #include <linux/percpu.h> |
| #include <linux/rcupdate.h> |
| #include <linux/gfp.h> |
| |
| struct percpu_ref; |
| typedef void (percpu_ref_func_t)(struct percpu_ref *); |
| |
| /* 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 { |
| /* |
| * 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. |
| */ |
| 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_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, 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 |
| * @ref: percpu_ref to kill |
| * |
| * Must be used to drop the initial ref on a percpu refcount; must be called |
| * precisely once before shutdown. |
| * |
| * 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) |
| { |
| 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; |
| } |
| |
| /** |
| * 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); |
| |
| rcu_read_unlock(); |
| } |
| |
| /** |
| * percpu_ref_get - increment a percpu refcount |
| * @ref: percpu_ref to get |
| * |
| * 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) |
| { |
| percpu_ref_get_many(ref, 1); |
| } |
| |
| /** |
| * 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; |
| |
| rcu_read_lock(); |
| |
| 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(); |
| |
| return ret; |
| } |
| |
| /** |
| * percpu_ref_tryget - try to increment a percpu refcount |
| * @ref: percpu_ref to try-get |
| * |
| * Increment a percpu refcount 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(struct percpu_ref *ref) |
| { |
| return percpu_ref_tryget_many(ref, 1); |
| } |
| |
| /** |
| * 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; |
| |
| WARN_ON_ONCE(!rcu_read_lock_held()); |
| |
| 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; |
| } |
| |
| /** |
| * 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_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_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_sub(*percpu_count, nr); |
| else if (unlikely(atomic_long_sub_and_test(nr, &ref->data->count))) |
| ref->data->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); |
| } |
| |
| /** |
| * 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 |