1/* SPDX-License-Identifier: GPL-2.0 */
  2
  3#ifndef _LINUX_OBJPOOL_H
  4#define _LINUX_OBJPOOL_H
  5
  6#include <linux/types.h>
  7#include <linux/refcount.h>
  8#include <linux/atomic.h>
  9#include <linux/cpumask.h>
 10#include <linux/irqflags.h>
 11#include <linux/smp.h>
 12
 13/*
 14 * objpool: ring-array based lockless MPMC queue
 15 *
 16 * Copyright: wuqiang.matt@bytedance.com,mhiramat@kernel.org
 17 *
 18 * objpool is a scalable implementation of high performance queue for
 19 * object allocation and reclamation, such as kretprobe instances.
 20 *
 21 * With leveraging percpu ring-array to mitigate hot spots of memory
 22 * contention, it delivers near-linear scalability for high parallel
 23 * scenarios. The objpool is best suited for the following cases:
 24 * 1) Memory allocation or reclamation are prohibited or too expensive
 25 * 2) Consumers are of different priorities, such as irqs and threads
 26 *
 27 * Limitations:
 28 * 1) Maximum objects (capacity) is fixed after objpool creation
 29 * 2) All pre-allocated objects are managed in percpu ring array,
 30 *    which consumes more memory than linked lists
 31 */
 32
 33/**
 34 * struct objpool_slot - percpu ring array of objpool
 35 * @head: head sequence of the local ring array (to retrieve at)
 36 * @tail: tail sequence of the local ring array (to append at)
 37 * @last: the last sequence number marked as ready for retrieve
 38 * @mask: bits mask for modulo capacity to compute array indexes
 39 * @entries: object entries on this slot
 40 *
 41 * Represents a cpu-local array-based ring buffer, its size is specialized
 42 * during initialization of object pool. The percpu objpool node is to be
 43 * allocated from local memory for NUMA system, and to be kept compact in
 44 * continuous memory: CPU assigned number of objects are stored just after
 45 * the body of objpool_node.
 46 *
 47 * Real size of the ring array is far too smaller than the value range of
 48 * head and tail, typed as uint32_t: [0, 2^32), so only lower bits (mask)
 49 * of head and tail are used as the actual position in the ring array. In
 50 * general the ring array is acting like a small sliding window, which is
 51 * always moving forward in the loop of [0, 2^32).
 52 */
 53struct objpool_slot {
 54	uint32_t            head;
 55	uint32_t            tail;
 56	uint32_t            last;
 57	uint32_t            mask;
 58	void               *entries[];
 59} __packed;
 60
 61struct objpool_head;
 62
 63/*
 64 * caller-specified callback for object initial setup, it's only called
 65 * once for each object (just after the memory allocation of the object)
 66 */
 67typedef int (*objpool_init_obj_cb)(void *obj, void *context);
 68
 69/* caller-specified cleanup callback for objpool destruction */
 70typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
 71
 72/**
 73 * struct objpool_head - object pooling metadata
 74 * @obj_size:   object size, aligned to sizeof(void *)
 75 * @nr_objs:    total objs (to be pre-allocated with objpool)
 76 * @nr_possible_cpus: cached value of num_possible_cpus()
 77 * @capacity:   max objs can be managed by one objpool_slot
 78 * @gfp:        gfp flags for kmalloc & vmalloc
 79 * @ref:        refcount of objpool
 80 * @flags:      flags for objpool management
 81 * @cpu_slots:  pointer to the array of objpool_slot
 82 * @release:    resource cleanup callback
 83 * @context:    caller-provided context
 84 */
 85struct objpool_head {
 86	int                     obj_size;
 87	int                     nr_objs;
 88	int                     nr_possible_cpus;
 89	int                     capacity;
 90	gfp_t                   gfp;
 91	refcount_t              ref;
 92	unsigned long           flags;
 93	struct objpool_slot   **cpu_slots;
 94	objpool_fini_cb         release;
 95	void                   *context;
 96};
 97
 98#define OBJPOOL_NR_OBJECT_MAX	(1UL << 24) /* maximum numbers of total objects */
 99#define OBJPOOL_OBJECT_SIZE_MAX	(1UL << 16) /* maximum size of an object */
100
101/**
102 * objpool_init() - initialize objpool and pre-allocated objects
103 * @pool:    the object pool to be initialized, declared by caller
104 * @nr_objs: total objects to be pre-allocated by this object pool
105 * @object_size: size of an object (should be > 0)
106 * @gfp:     flags for memory allocation (via kmalloc or vmalloc)
107 * @context: user context for object initialization callback
108 * @objinit: object initialization callback for extra setup
109 * @release: cleanup callback for extra cleanup task
110 *
111 * return value: 0 for success, otherwise error code
112 *
113 * All pre-allocated objects are to be zeroed after memory allocation.
114 * Caller could do extra initialization in objinit callback. objinit()
115 * will be called just after slot allocation and called only once for
116 * each object. After that the objpool won't touch any content of the
117 * objects. It's caller's duty to perform reinitialization after each
118 * pop (object allocation) or do clearance before each push (object
119 * reclamation).
120 */
121int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
122		 gfp_t gfp, void *context, objpool_init_obj_cb objinit,
123		 objpool_fini_cb release);
124
125/* try to retrieve object from slot */
126static inline void *__objpool_try_get_slot(struct objpool_head *pool, int cpu)
127{
128	struct objpool_slot *slot = pool->cpu_slots[cpu];
129	/* load head snapshot, other cpus may change it */
130	uint32_t head = smp_load_acquire(&slot->head);
131
132	while (head != READ_ONCE(slot->last)) {
133		void *obj;
134
135		/*
136		 * data visibility of 'last' and 'head' could be out of
137		 * order since memory updating of 'last' and 'head' are
138		 * performed in push() and pop() independently
139		 *
140		 * before any retrieving attempts, pop() must guarantee
141		 * 'last' is behind 'head', that is to say, there must
142		 * be available objects in slot, which could be ensured
143		 * by condition 'last != head && last - head <= nr_objs'
144		 * that is equivalent to 'last - head - 1 < nr_objs' as
145		 * 'last' and 'head' are both unsigned int32
146		 */
147		if (READ_ONCE(slot->last) - head - 1 >= pool->nr_objs) {
148			head = READ_ONCE(slot->head);
149			continue;
150		}
151
152		/* obj must be retrieved before moving forward head */
153		obj = READ_ONCE(slot->entries[head & slot->mask]);
154
155		/* move head forward to mark it's consumption */
156		if (try_cmpxchg_release(&slot->head, &head, head + 1))
157			return obj;
158	}
159
160	return NULL;
161}
162
163/**
164 * objpool_pop() - allocate an object from objpool
165 * @pool: object pool
166 *
167 * return value: object ptr or NULL if failed
168 */
169static inline void *objpool_pop(struct objpool_head *pool)
170{
171	void *obj = NULL;
172	unsigned long flags;
173	int i, cpu;
174
175	/* disable local irq to avoid preemption & interruption */
176	raw_local_irq_save(flags);
177
178	cpu = raw_smp_processor_id();
179	for (i = 0; i < pool->nr_possible_cpus; i++) {
180		obj = __objpool_try_get_slot(pool, cpu);
181		if (obj)
182			break;
183		cpu = cpumask_next_wrap(cpu, cpu_possible_mask, -1, 1);
184	}
185	raw_local_irq_restore(flags);
186
187	return obj;
188}
189
190/* adding object to slot, abort if the slot was already full */
191static inline int
192__objpool_try_add_slot(void *obj, struct objpool_head *pool, int cpu)
193{
194	struct objpool_slot *slot = pool->cpu_slots[cpu];
195	uint32_t head, tail;
196
197	/* loading tail and head as a local snapshot, tail first */
198	tail = READ_ONCE(slot->tail);
199
200	do {
201		head = READ_ONCE(slot->head);
202		/* fault caught: something must be wrong */
203		WARN_ON_ONCE(tail - head > pool->nr_objs);
204	} while (!try_cmpxchg_acquire(&slot->tail, &tail, tail + 1));
205
206	/* now the tail position is reserved for the given obj */
207	WRITE_ONCE(slot->entries[tail & slot->mask], obj);
208	/* update sequence to make this obj available for pop() */
209	smp_store_release(&slot->last, tail + 1);
210
211	return 0;
212}
213
214/**
215 * objpool_push() - reclaim the object and return back to objpool
216 * @obj:  object ptr to be pushed to objpool
217 * @pool: object pool
218 *
219 * return: 0 or error code (it fails only when user tries to push
220 * the same object multiple times or wrong "objects" into objpool)
221 */
222static inline int objpool_push(void *obj, struct objpool_head *pool)
223{
224	unsigned long flags;
225	int rc;
226
227	/* disable local irq to avoid preemption & interruption */
228	raw_local_irq_save(flags);
229	rc = __objpool_try_add_slot(obj, pool, raw_smp_processor_id());
230	raw_local_irq_restore(flags);
231
232	return rc;
233}
234
235
236/**
237 * objpool_drop() - discard the object and deref objpool
238 * @obj:  object ptr to be discarded
239 * @pool: object pool
240 *
241 * return: 0 if objpool was released; -EAGAIN if there are still
242 *         outstanding objects
243 *
244 * objpool_drop is normally for the release of outstanding objects
245 * after objpool cleanup (objpool_fini). Thinking of this example:
246 * kretprobe is unregistered and objpool_fini() is called to release
247 * all remained objects, but there are still objects being used by
248 * unfinished kretprobes (like blockable function: sys_accept). So
249 * only when the last outstanding object is dropped could the whole
250 * objpool be released along with the call of objpool_drop()
251 */
252int objpool_drop(void *obj, struct objpool_head *pool);
253
254/**
255 * objpool_free() - release objpool forcely (all objects to be freed)
256 * @pool: object pool to be released
257 */
258void objpool_free(struct objpool_head *pool);
259
260/**
261 * objpool_fini() - deref object pool (also releasing unused objects)
262 * @pool: object pool to be dereferenced
263 *
264 * objpool_fini() will try to release all remained free objects and
265 * then drop an extra reference of the objpool. If all objects are
266 * already returned to objpool (so called synchronous use cases),
267 * the objpool itself will be freed together. But if there are still
268 * outstanding objects (so called asynchronous use cases, such like
269 * blockable kretprobe), the objpool won't be released until all
270 * the outstanding objects are dropped, but the caller must assure
271 * there are no concurrent objpool_push() on the fly. Normally RCU
272 * is being required to make sure all ongoing objpool_push() must
273 * be finished before calling objpool_fini(), so does test_objpool,
274 * kretprobe or rethook
275 */
276void objpool_fini(struct objpool_head *pool);
277
278#endif /* _LINUX_OBJPOOL_H */