include/linux/objpool.h - kernel/common - Git at Google

 /* SPDX-License-Identifier: GPL-2.0 */

 #ifndef _LINUX_OBJPOOL_H
 #define _LINUX_OBJPOOL_H

 #include <linux/types.h>
 #include <linux/refcount.h>
 #include <linux/atomic.h>
 #include <linux/cpumask.h>
 #include <linux/irqflags.h>
 #include <linux/smp.h>

 /*
  * objpool: ring-array based lockless MPMC queue
  *
  * Copyright: [email protected],[email protected]
  *
  * objpool is a scalable implementation of high performance queue for
  * object allocation and reclamation, such as kretprobe instances.
  *
  * With leveraging percpu ring-array to mitigate hot spots of memory
  * contention, it delivers near-linear scalability for high parallel
  * scenarios. The objpool is best suited for the following cases:
  * 1) Memory allocation or reclamation are prohibited or too expensive
  * 2) Consumers are of different priorities, such as irqs and threads
  *
  * Limitations:
  * 1) Maximum objects (capacity) is fixed after objpool creation
  * 2) All pre-allocated objects are managed in percpu ring array,
  *    which consumes more memory than linked lists
  */

 /**
  * struct objpool_slot - percpu ring array of objpool
  * @head: head sequence of the local ring array (to retrieve at)
  * @tail: tail sequence of the local ring array (to append at)
  * @last: the last sequence number marked as ready for retrieve
  * @mask: bits mask for modulo capacity to compute array indexes
  * @entries: object entries on this slot
  *
  * Represents a cpu-local array-based ring buffer, its size is specialized
  * during initialization of object pool. The percpu objpool node is to be
  * allocated from local memory for NUMA system, and to be kept compact in
  * continuous memory: CPU assigned number of objects are stored just after
  * the body of objpool_node.
  *
  * Real size of the ring array is far too smaller than the value range of
  * head and tail, typed as uint32_t: [0, 2^32), so only lower bits (mask)
  * of head and tail are used as the actual position in the ring array. In
  * general the ring array is acting like a small sliding window, which is
  * always moving forward in the loop of [0, 2^32).
  */
 struct objpool_slot {
 	uint32_t            head;
 	uint32_t            tail;
 	uint32_t            last;
 	uint32_t            mask;
 	void               *entries[];
 } __packed;

 struct objpool_head;

 /*
  * caller-specified callback for object initial setup, it's only called
  * once for each object (just after the memory allocation of the object)
  */
 typedef int (*objpool_init_obj_cb)(void *obj, void *context);

 /* caller-specified cleanup callback for objpool destruction */
 typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);

 /**
  * struct objpool_head - object pooling metadata
  * @obj_size:   object size, aligned to sizeof(void *)
  * @nr_objs:    total objs (to be pre-allocated with objpool)
  * @nr_possible_cpus: cached value of num_possible_cpus()
  * @capacity:   max objs can be managed by one objpool_slot
  * @gfp:        gfp flags for kmalloc & vmalloc
  * @ref:        refcount of objpool
  * @flags:      flags for objpool management
  * @cpu_slots:  pointer to the array of objpool_slot
  * @release:    resource cleanup callback
  * @context:    caller-provided context
  */
 struct objpool_head {
 	int                     obj_size;
 	int                     nr_objs;
 	int                     nr_possible_cpus;
 	int                     capacity;
 	gfp_t                   gfp;
 	refcount_t              ref;
 	unsigned long           flags;
 	struct objpool_slot   **cpu_slots;
 	objpool_fini_cb         release;
 	void                   *context;
 };

 #define OBJPOOL_NR_OBJECT_MAX	(1UL << 24) /* maximum numbers of total objects */
 #define OBJPOOL_OBJECT_SIZE_MAX	(1UL << 16) /* maximum size of an object */

 /**
  * objpool_init() - initialize objpool and pre-allocated objects
  * @pool:    the object pool to be initialized, declared by caller
  * @nr_objs: total objects to be pre-allocated by this object pool
  * @object_size: size of an object (should be > 0)
  * @gfp:     flags for memory allocation (via kmalloc or vmalloc)
  * @context: user context for object initialization callback
  * @objinit: object initialization callback for extra setup
  * @release: cleanup callback for extra cleanup task
  *
  * return value: 0 for success, otherwise error code
  *
  * All pre-allocated objects are to be zeroed after memory allocation.
  * Caller could do extra initialization in objinit callback. objinit()
  * will be called just after slot allocation and called only once for
  * each object. After that the objpool won't touch any content of the
  * objects. It's caller's duty to perform reinitialization after each
  * pop (object allocation) or do clearance before each push (object
  * reclamation).
  */
 int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
 		 gfp_t gfp, void *context, objpool_init_obj_cb objinit,
 		 objpool_fini_cb release);

 /* try to retrieve object from slot */
 static inline void *__objpool_try_get_slot(struct objpool_head *pool, int cpu)
 {
 	struct objpool_slot *slot = pool->cpu_slots[cpu];
 	/* load head snapshot, other cpus may change it */
 	uint32_t head = smp_load_acquire(&slot->head);

 	while (head != READ_ONCE(slot->last)) {
 		void *obj;

 		/*
 		 * data visibility of 'last' and 'head' could be out of
 		 * order since memory updating of 'last' and 'head' are
 		 * performed in push() and pop() independently
 		 *
 		 * before any retrieving attempts, pop() must guarantee
 		 * 'last' is behind 'head', that is to say, there must
 		 * be available objects in slot, which could be ensured
 		 * by condition 'last != head && last - head <= nr_objs'
 		 * that is equivalent to 'last - head - 1 < nr_objs' as
 		 * 'last' and 'head' are both unsigned int32
 		 */
 		if (READ_ONCE(slot->last) - head - 1 >= pool->nr_objs) {
 			head = READ_ONCE(slot->head);
 			continue;
 		}

 		/* obj must be retrieved before moving forward head */
 		obj = READ_ONCE(slot->entries[head & slot->mask]);

 		/* move head forward to mark it's consumption */
 		if (try_cmpxchg_release(&slot->head, &head, head + 1))
 			return obj;
 	}

 	return NULL;
 }

 /**
  * objpool_pop() - allocate an object from objpool
  * @pool: object pool
  *
  * return value: object ptr or NULL if failed
  */
 static inline void *objpool_pop(struct objpool_head *pool)
 {
 	void *obj = NULL;
 	unsigned long flags;
 	int i, cpu;

 	/* disable local irq to avoid preemption & interruption */
 	raw_local_irq_save(flags);

 	cpu = raw_smp_processor_id();
 	for (i = 0; i < pool->nr_possible_cpus; i++) {
 		obj = __objpool_try_get_slot(pool, cpu);
 		if (obj)
 			break;
 		cpu = cpumask_next_wrap(cpu, cpu_possible_mask, -1, 1);
 	}
 	raw_local_irq_restore(flags);

 	return obj;
 }

 /* adding object to slot, abort if the slot was already full */
 static inline int
 __objpool_try_add_slot(void *obj, struct objpool_head *pool, int cpu)
 {
 	struct objpool_slot *slot = pool->cpu_slots[cpu];
 	uint32_t head, tail;

 	/* loading tail and head as a local snapshot, tail first */
 	tail = READ_ONCE(slot->tail);

 	do {
 		head = READ_ONCE(slot->head);
 		/* fault caught: something must be wrong */
 		WARN_ON_ONCE(tail - head > pool->nr_objs);
 	} while (!try_cmpxchg_acquire(&slot->tail, &tail, tail + 1));

 	/* now the tail position is reserved for the given obj */
 	WRITE_ONCE(slot->entries[tail & slot->mask], obj);
 	/* update sequence to make this obj available for pop() */
 	smp_store_release(&slot->last, tail + 1);

 	return 0;
 }

 /**
  * objpool_push() - reclaim the object and return back to objpool
  * @obj:  object ptr to be pushed to objpool
  * @pool: object pool
  *
  * return: 0 or error code (it fails only when user tries to push
  * the same object multiple times or wrong "objects" into objpool)
  */
 static inline int objpool_push(void *obj, struct objpool_head *pool)
 {
 	unsigned long flags;
 	int rc;

 	/* disable local irq to avoid preemption & interruption */
 	raw_local_irq_save(flags);
 	rc = __objpool_try_add_slot(obj, pool, raw_smp_processor_id());
 	raw_local_irq_restore(flags);

 	return rc;
 }


 /**
  * objpool_drop() - discard the object and deref objpool
  * @obj:  object ptr to be discarded
  * @pool: object pool
  *
  * return: 0 if objpool was released; -EAGAIN if there are still
  *         outstanding objects
  *
  * objpool_drop is normally for the release of outstanding objects
  * after objpool cleanup (objpool_fini). Thinking of this example:
  * kretprobe is unregistered and objpool_fini() is called to release
  * all remained objects, but there are still objects being used by
  * unfinished kretprobes (like blockable function: sys_accept). So
  * only when the last outstanding object is dropped could the whole
  * objpool be released along with the call of objpool_drop()
  */
 int objpool_drop(void *obj, struct objpool_head *pool);

 /**
  * objpool_free() - release objpool forcely (all objects to be freed)
  * @pool: object pool to be released
  */
 void objpool_free(struct objpool_head *pool);

 /**
  * objpool_fini() - deref object pool (also releasing unused objects)
  * @pool: object pool to be dereferenced
  *
  * objpool_fini() will try to release all remained free objects and
  * then drop an extra reference of the objpool. If all objects are
  * already returned to objpool (so called synchronous use cases),
  * the objpool itself will be freed together. But if there are still
  * outstanding objects (so called asynchronous use cases, such like
  * blockable kretprobe), the objpool won't be released until all
  * the outstanding objects are dropped, but the caller must assure
  * there are no concurrent objpool_push() on the fly. Normally RCU
  * is being required to make sure all ongoing objpool_push() must
  * be finished before calling objpool_fini(), so does test_objpool,
  * kretprobe or rethook
  */
 void objpool_fini(struct objpool_head *pool);

 #endif /* _LINUX_OBJPOOL_H */
	/* SPDX-License-Identifier: GPL-2.0 */

	#ifndef _LINUX_OBJPOOL_H
	#define _LINUX_OBJPOOL_H

	#include <linux/types.h>
	#include <linux/refcount.h>
	#include <linux/atomic.h>
	#include <linux/cpumask.h>
	#include <linux/irqflags.h>
	#include <linux/smp.h>

	/*
	* objpool: ring-array based lockless MPMC queue
	*
	* Copyright: [email protected],[email protected]
	*
	* objpool is a scalable implementation of high performance queue for
	* object allocation and reclamation, such as kretprobe instances.
	*
	* With leveraging percpu ring-array to mitigate hot spots of memory
	* contention, it delivers near-linear scalability for high parallel
	* scenarios. The objpool is best suited for the following cases:
	* 1) Memory allocation or reclamation are prohibited or too expensive
	* 2) Consumers are of different priorities, such as irqs and threads
	*
	* Limitations:
	* 1) Maximum objects (capacity) is fixed after objpool creation
	* 2) All pre-allocated objects are managed in percpu ring array,
	* which consumes more memory than linked lists
	*/

	/**
	* struct objpool_slot - percpu ring array of objpool
	* @head: head sequence of the local ring array (to retrieve at)
	* @tail: tail sequence of the local ring array (to append at)
	* @last: the last sequence number marked as ready for retrieve
	* @mask: bits mask for modulo capacity to compute array indexes
	* @entries: object entries on this slot
	*
	* Represents a cpu-local array-based ring buffer, its size is specialized
	* during initialization of object pool. The percpu objpool node is to be
	* allocated from local memory for NUMA system, and to be kept compact in
	* continuous memory: CPU assigned number of objects are stored just after
	* the body of objpool_node.
	*
	* Real size of the ring array is far too smaller than the value range of
	* head and tail, typed as uint32_t: [0, 2^32), so only lower bits (mask)
	* of head and tail are used as the actual position in the ring array. In
	* general the ring array is acting like a small sliding window, which is
	* always moving forward in the loop of [0, 2^32).
	*/
	struct objpool_slot {
	uint32_t head;
	uint32_t tail;
	uint32_t last;
	uint32_t mask;
	void *entries[];
	} __packed;

	struct objpool_head;

	/*
	* caller-specified callback for object initial setup, it's only called
	* once for each object (just after the memory allocation of the object)
	*/
	typedef int (objpool_init_obj_cb)(void obj, void *context);

	/* caller-specified cleanup callback for objpool destruction */
	typedef int (objpool_fini_cb)(struct objpool_head head, void *context);

	/**
	* struct objpool_head - object pooling metadata
	* @obj_size: object size, aligned to sizeof(void *)
	* @nr_objs: total objs (to be pre-allocated with objpool)
	* @nr_possible_cpus: cached value of num_possible_cpus()
	* @capacity: max objs can be managed by one objpool_slot
	* @gfp: gfp flags for kmalloc & vmalloc
	* @ref: refcount of objpool
	* @flags: flags for objpool management
	* @cpu_slots: pointer to the array of objpool_slot
	* @release: resource cleanup callback
	* @context: caller-provided context
	*/
	struct objpool_head {
	int obj_size;
	int nr_objs;
	int nr_possible_cpus;
	int capacity;
	gfp_t gfp;
	refcount_t ref;
	unsigned long flags;
	struct objpool_slot **cpu_slots;
	objpool_fini_cb release;
	void *context;
	};

	#define OBJPOOL_NR_OBJECT_MAX (1UL << 24) /* maximum numbers of total objects */
	#define OBJPOOL_OBJECT_SIZE_MAX (1UL << 16) /* maximum size of an object */

	/**
	* objpool_init() - initialize objpool and pre-allocated objects
	* @pool: the object pool to be initialized, declared by caller
	* @nr_objs: total objects to be pre-allocated by this object pool
	* @object_size: size of an object (should be > 0)
	* @gfp: flags for memory allocation (via kmalloc or vmalloc)
	* @context: user context for object initialization callback
	* @objinit: object initialization callback for extra setup
	* @release: cleanup callback for extra cleanup task
	*
	* return value: 0 for success, otherwise error code
	*
	* All pre-allocated objects are to be zeroed after memory allocation.
	* Caller could do extra initialization in objinit callback. objinit()
	* will be called just after slot allocation and called only once for
	* each object. After that the objpool won't touch any content of the
	* objects. It's caller's duty to perform reinitialization after each
	* pop (object allocation) or do clearance before each push (object
	* reclamation).
	*/
	int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
	gfp_t gfp, void *context, objpool_init_obj_cb objinit,
	objpool_fini_cb release);

	/* try to retrieve object from slot */
	static inline void __objpool_try_get_slot(struct objpool_head pool, int cpu)
	{
	struct objpool_slot *slot = pool->cpu_slots[cpu];
	/* load head snapshot, other cpus may change it */
	uint32_t head = smp_load_acquire(&slot->head);

	while (head != READ_ONCE(slot->last)) {
	void *obj;

	/*
	* data visibility of 'last' and 'head' could be out of
	* order since memory updating of 'last' and 'head' are
	* performed in push() and pop() independently
	*
	* before any retrieving attempts, pop() must guarantee
	* 'last' is behind 'head', that is to say, there must
	* be available objects in slot, which could be ensured
	* by condition 'last != head && last - head <= nr_objs'
	* that is equivalent to 'last - head - 1 < nr_objs' as
	* 'last' and 'head' are both unsigned int32
	*/
	if (READ_ONCE(slot->last) - head - 1 >= pool->nr_objs) {
	head = READ_ONCE(slot->head);
	continue;
	}

	/* obj must be retrieved before moving forward head */
	obj = READ_ONCE(slot->entries[head & slot->mask]);

	/* move head forward to mark it's consumption */
	if (try_cmpxchg_release(&slot->head, &head, head + 1))
	return obj;
	}

	return NULL;
	}

	/**
	* objpool_pop() - allocate an object from objpool
	* @pool: object pool
	*
	* return value: object ptr or NULL if failed
	*/
	static inline void objpool_pop(struct objpool_head pool)
	{
	void *obj = NULL;
	unsigned long flags;
	int i, cpu;

	/* disable local irq to avoid preemption & interruption */
	raw_local_irq_save(flags);

	cpu = raw_smp_processor_id();
	for (i = 0; i < pool->nr_possible_cpus; i++) {
	obj = __objpool_try_get_slot(pool, cpu);
	if (obj)
	break;
	cpu = cpumask_next_wrap(cpu, cpu_possible_mask, -1, 1);
	}
	raw_local_irq_restore(flags);

	return obj;
	}

	/* adding object to slot, abort if the slot was already full */
	static inline int
	__objpool_try_add_slot(void obj, struct objpool_head pool, int cpu)
	{
	struct objpool_slot *slot = pool->cpu_slots[cpu];
	uint32_t head, tail;

	/* loading tail and head as a local snapshot, tail first */
	tail = READ_ONCE(slot->tail);

	do {
	head = READ_ONCE(slot->head);
	/* fault caught: something must be wrong */
	WARN_ON_ONCE(tail - head > pool->nr_objs);
	} while (!try_cmpxchg_acquire(&slot->tail, &tail, tail + 1));

	/* now the tail position is reserved for the given obj */
	WRITE_ONCE(slot->entries[tail & slot->mask], obj);
	/* update sequence to make this obj available for pop() */
	smp_store_release(&slot->last, tail + 1);

	return 0;
	}

	/**
	* objpool_push() - reclaim the object and return back to objpool
	* @obj: object ptr to be pushed to objpool
	* @pool: object pool
	*
	* return: 0 or error code (it fails only when user tries to push
	* the same object multiple times or wrong "objects" into objpool)
	*/
	static inline int objpool_push(void obj, struct objpool_head pool)
	{
	unsigned long flags;
	int rc;

	/* disable local irq to avoid preemption & interruption */
	raw_local_irq_save(flags);
	rc = __objpool_try_add_slot(obj, pool, raw_smp_processor_id());
	raw_local_irq_restore(flags);

	return rc;
	}


	/**
	* objpool_drop() - discard the object and deref objpool
	* @obj: object ptr to be discarded
	* @pool: object pool
	*
	* return: 0 if objpool was released; -EAGAIN if there are still
	* outstanding objects
	*
	* objpool_drop is normally for the release of outstanding objects
	* after objpool cleanup (objpool_fini). Thinking of this example:
	* kretprobe is unregistered and objpool_fini() is called to release
	* all remained objects, but there are still objects being used by
	* unfinished kretprobes (like blockable function: sys_accept). So
	* only when the last outstanding object is dropped could the whole
	* objpool be released along with the call of objpool_drop()
	*/
	int objpool_drop(void obj, struct objpool_head pool);

	/**
	* objpool_free() - release objpool forcely (all objects to be freed)
	* @pool: object pool to be released
	*/
	void objpool_free(struct objpool_head *pool);

	/**
	* objpool_fini() - deref object pool (also releasing unused objects)
	* @pool: object pool to be dereferenced
	*
	* objpool_fini() will try to release all remained free objects and
	* then drop an extra reference of the objpool. If all objects are
	* already returned to objpool (so called synchronous use cases),
	* the objpool itself will be freed together. But if there are still
	* outstanding objects (so called asynchronous use cases, such like
	* blockable kretprobe), the objpool won't be released until all
	* the outstanding objects are dropped, but the caller must assure
	* there are no concurrent objpool_push() on the fly. Normally RCU
	* is being required to make sure all ongoing objpool_push() must
	* be finished before calling objpool_fini(), so does test_objpool,
	* kretprobe or rethook
	*/
	void objpool_fini(struct objpool_head *pool);

	#endif /* _LINUX_OBJPOOL_H */