Merge tag 'probes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull probes updates from Masami Hiramatsu:
"Cleanups:

- kprobes: Fixes typo in kprobes samples

- tracing/eprobes: Remove 'break' after return

kretprobe/fprobe performance improvements:

- lib: Introduce new `objpool`, which is a high performance lockless
object queue. This uses per-cpu ring array to allocate/release
objects from the pre-allocated object pool.

Since the index of ring array is a 32bit sequential counter, we can
retry to push/pop the object pointer from the ring without lock (as
seq-lock does)

- lib: Add an objpool test module to test the functionality and
evaluate the performance under some circumstances

- kprobes/fprobe: Improve kretprobe and rethook scalability
performance with objpool.

This improves both legacy kretprobe and fprobe exit handler (which
is based on rethook) to be scalable on SMP systems. Even with
8-threads parallel test, it shows a great scalability improvement

- Remove unneeded freelist.h which is replaced by objpool

- objpool: Add maintainers entry for the objpool

- objpool: Fix to remove unused include header lines"

* tag 'probes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
kprobes: unused header files removed
MAINTAINERS: objpool added
kprobes: freelist.h removed
kprobes: kretprobe scalability improvement
lib: objpool test module added
lib: objpool added: ring-array based lockless MPMC
tracing/eprobe: drop unneeded breaks
samples: kprobes: Fixes a typo

MAINTAINERS

···
 F:	lib/objagg.c
 F:	lib/test_objagg.c
 
+OBJPOOL
+M:	Matt Wu <[e-mail]>
+S:	Supported
+F:	include/linux/objpool.h
+F:	lib/objpool.c
+F:	lib/test_objpool.c
+
 OBJTOOL
 M:	Josh Poimboeuf <[e-mail]>
 M:	Peter Zijlstra <[e-mail]>

include/linux/freelist.h

···
-/* SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause */
-#ifndef FREELIST_H
-#define FREELIST_H
-
-#include <linux/atomic.h>
-
-/*
- * Copyright: [e-mail]
- *
- * A simple CAS-based lock-free free list. Not the fastest thing in the world
- * under heavy contention, but simple and correct (assuming nodes are never
- * freed until after the free list is destroyed), and fairly speedy under low
- * contention.
- *
- * Adapted from: https://moodycamel.com/blog/2014/solving-the-aba-problem-for-lock-free-free-lists
- */
-
-struct freelist_node {
-	atomic_t		refs;
-	struct freelist_node	*next;
-};
-
-struct freelist_head {
-	struct freelist_node	*head;
-};
-
-#define REFS_ON_FREELIST 0x80000000
-#define REFS_MASK	 0x7FFFFFFF
-
-static inline void __freelist_add(struct freelist_node *node, struct freelist_head *list)
-{
-	/*
-	 * Since the refcount is zero, and nobody can increase it once it's
-	 * zero (except us, and we run only one copy of this method per node at
-	 * a time, i.e. the single thread case), then we know we can safely
-	 * change the next pointer of the node; however, once the refcount is
-	 * back above zero, then other threads could increase it (happens under
-	 * heavy contention, when the refcount goes to zero in between a load
-	 * and a refcount increment of a node in try_get, then back up to
-	 * something non-zero, then the refcount increment is done by the other
-	 * thread) -- so if the CAS to add the node to the actual list fails,
-	 * decrese the refcount and leave the add operation to the next thread
-	 * who puts the refcount back to zero (which could be us, hence the
-	 * loop).
-	 */
-	struct freelist_node *head = READ_ONCE(list->head);
-
-	for (;;) {
-		WRITE_ONCE(node->next, head);
-		atomic_set_release(&node->refs, 1);
-
-		if (!try_cmpxchg_release(&list->head, &head, node)) {
-			/*
-			 * Hmm, the add failed, but we can only try again when
-			 * the refcount goes back to zero.
-			 */
-			if (atomic_fetch_add_release(REFS_ON_FREELIST - 1, &node->refs) == 1)
-				continue;
-		}
-		return;
-	}
-}
-
-static inline void freelist_add(struct freelist_node *node, struct freelist_head *list)
-{
-	/*
-	 * We know that the should-be-on-freelist bit is 0 at this point, so
-	 * it's safe to set it using a fetch_add.
-	 */
-	if (!atomic_fetch_add_release(REFS_ON_FREELIST, &node->refs)) {
-		/*
-		 * Oh look! We were the last ones referencing this node, and we
-		 * know we want to add it to the free list, so let's do it!
-		 */
-		__freelist_add(node, list);
-	}
-}
-
-static inline struct freelist_node *freelist_try_get(struct freelist_head *list)
-{
-	struct freelist_node *prev, *next, *head = smp_load_acquire(&list->head);
-	unsigned int refs;
-
-	while (head) {
-		prev = head;
-		refs = atomic_read(&head->refs);
-		if ((refs & REFS_MASK) == 0 ||
-		    !atomic_try_cmpxchg_acquire(&head->refs, &refs, refs+1)) {
-			head = smp_load_acquire(&list->head);
-			continue;
-		}
-
-		/*
-		 * Good, reference count has been incremented (it wasn't at
-		 * zero), which means we can read the next and not worry about
-		 * it changing between now and the time we do the CAS.
-		 */
-		next = READ_ONCE(head->next);
-		if (try_cmpxchg_acquire(&list->head, &head, next)) {
-			/*
-			 * Yay, got the node. This means it was on the list,
-			 * which means should-be-on-freelist must be false no
-			 * matter the refcount (because nobody else knows it's
-			 * been taken off yet, it can't have been put back on).
-			 */
-			WARN_ON_ONCE(atomic_read(&head->refs) & REFS_ON_FREELIST);
-
-			/*
-			 * Decrease refcount twice, once for our ref, and once
-			 * for the list's ref.
-			 */
-			atomic_fetch_add(-2, &head->refs);
-
-			return head;
-		}
-
-		/*
-		 * OK, the head must have changed on us, but we still need to decrement
-		 * the refcount we increased.
-		 */
-		refs = atomic_fetch_add(-1, &prev->refs);
-		if (refs == REFS_ON_FREELIST + 1)
-			__freelist_add(prev, list);
-	}
-
-	return NULL;
-}
-
-#endif /* FREELIST_H */

include/linux/kprobes.h

···
 #include <linux/rcupdate.h>
 #include <linux/mutex.h>
 #include <linux/ftrace.h>
-#include <linux/refcount.h>
-#include <linux/freelist.h>
+#include <linux/objpool.h>
 #include <linux/rethook.h>
 #include <asm/kprobes.h>
 
···
  */
 struct kretprobe_holder {
 	struct kretprobe	*rp;
-	refcount_t		ref;
+	struct objpool_head	pool;
 };
 
 struct kretprobe {
···
 #ifdef CONFIG_KRETPROBE_ON_RETHOOK
 	struct rethook *rh;
 #else
-	struct freelist_head freelist;
 	struct kretprobe_holder *rph;
 #endif
 };
···
 #ifdef CONFIG_KRETPROBE_ON_RETHOOK
 	struct rethook_node node;
 #else
-	union {
-		struct freelist_node freelist;
-		struct rcu_head rcu;
-	};
+	struct rcu_head rcu;
 	struct llist_node llist;
 	struct kretprobe_holder *rph;
 	kprobe_opcode_t *ret_addr;

include/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>
+
+/*
+ * objpool: ring-array based lockless MPMC queue
+ *
+ * Copyright: [e-mail],[e-mail]
+ *
+ * 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_cpus:    local copy of nr_cpu_ids
+ * @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_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);
+
+/**
+ * objpool_pop() - allocate an object from objpool
+ * @pool: object pool
+ *
+ * return value: object ptr or NULL if failed
+ */
+void *objpool_pop(struct objpool_head *pool);
+
+/**
+ * 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)
+ */
+int objpool_push(void *obj, struct objpool_head *pool);
+
+/**
+ * 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 */

include/linux/rethook.h

···
 #define _LINUX_RETHOOK_H
 
 #include <linux/compiler.h>
-#include <linux/freelist.h>
+#include <linux/objpool.h>
 #include <linux/kallsyms.h>
 #include <linux/llist.h>
 #include <linux/rcupdate.h>
-#include <linux/refcount.h>
 
 struct rethook_node;
 
···
 struct rethook {
 	void			*data;
 	rethook_handler_t	handler;
-	struct freelist_head	pool;
-	refcount_t		ref;
+	struct objpool_head	pool;
 	struct rcu_head		rcu;
 };
 
 /**
  * struct rethook_node - The rethook shadow-stack entry node.
- * @freelist: The freelist, linked to struct rethook::pool.
  * @rcu: The rcu_head for deferred freeing.
  * @llist: The llist, linked to a struct task_struct::rethooks.
  * @rethook: The pointer to the struct rethook.
···
  * on each entry of the shadow stack.
  */
 struct rethook_node {
-	union {
-		struct freelist_node freelist;
-		struct rcu_head      rcu;
-	};
+	struct rcu_head		rcu;
 	struct llist_node	llist;
 	struct rethook		*rethook;
 	unsigned long		ret_addr;
 	unsigned long		frame;
 };
 
-struct rethook *rethook_alloc(void *data, rethook_handler_t handler);
+struct rethook *rethook_alloc(void *data, rethook_handler_t handler, int size, int num);
 void rethook_stop(struct rethook *rh);
 void rethook_free(struct rethook *rh);
-void rethook_add_node(struct rethook *rh, struct rethook_node *node);
 struct rethook_node *rethook_try_get(struct rethook *rh);
 void rethook_recycle(struct rethook_node *node);
 void rethook_hook(struct rethook_node *node, struct pt_regs *regs, bool mcount);
···
 #endif
 
 #endif
-

kernel/kprobes.c

···
 #ifdef CONFIG_KRETPROBES
 
 #if !defined(CONFIG_KRETPROBE_ON_RETHOOK)
+
+/* callbacks for objpool of kretprobe instances */
+static int kretprobe_init_inst(void *nod, void *context)
+{
+	struct kretprobe_instance *ri = nod;
+
+	ri->rph = context;
+	return 0;
+}
+static int kretprobe_fini_pool(struct objpool_head *head, void *context)
+{
+	kfree(context);
+	return 0;
+}
+
 static void free_rp_inst_rcu(struct rcu_head *head)
 {
 	struct kretprobe_instance *ri = container_of(head, struct kretprobe_instance, rcu);
+	struct kretprobe_holder *rph = ri->rph;
 
-	if (refcount_dec_and_test(&ri->rph->ref))
-		kfree(ri->rph);
-	kfree(ri);
+	objpool_drop(ri, &rph->pool);
 }
 NOKPROBE_SYMBOL(free_rp_inst_rcu);
 
···
 	struct kretprobe *rp = get_kretprobe(ri);
 
 	if (likely(rp))
-		freelist_add(&ri->freelist, &rp->freelist);
+		objpool_push(ri, &rp->rph->pool);
 	else
 		call_rcu(&ri->rcu, free_rp_inst_rcu);
 }
···
 
 static inline void free_rp_inst(struct kretprobe *rp)
 {
-	struct kretprobe_instance *ri;
-	struct freelist_node *node;
-	int count = 0;
+	struct kretprobe_holder *rph = rp->rph;
 
-	node = rp->freelist.head;
-	while (node) {
-		ri = container_of(node, struct kretprobe_instance, freelist);
-		node = node->next;
-
-		kfree(ri);
-		count++;
-	}
-
-	if (refcount_sub_and_test(count, &rp->rph->ref)) {
-		kfree(rp->rph);
-		rp->rph = NULL;
-	}
+	if (!rph)
+		return;
+	rp->rph = NULL;
+	objpool_fini(&rph->pool);
 }
 
 /* This assumes the 'tsk' is the current task or the is not running. */
···
 static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
 {
 	struct kretprobe *rp = container_of(p, struct kretprobe, kp);
+	struct kretprobe_holder *rph = rp->rph;
 	struct kretprobe_instance *ri;
-	struct freelist_node *fn;
 
-	fn = freelist_try_get(&rp->freelist);
-	if (!fn) {
+	ri = objpool_pop(&rph->pool);
+	if (!ri) {
 		rp->nmissed++;
 		return 0;
 	}
 
-	ri = container_of(fn, struct kretprobe_instance, freelist);
-
 	if (rp->entry_handler && rp->entry_handler(ri, regs)) {
-		freelist_add(&ri->freelist, &rp->freelist);
+		objpool_push(ri, &rph->pool);
 		return 0;
 	}
 
···
 int register_kretprobe(struct kretprobe *rp)
 {
 	int ret;
-	struct kretprobe_instance *inst;
 	int i;
 	void *addr;
 
···
 		rp->maxactive = max_t(unsigned int, 10, 2*num_possible_cpus());
 
 #ifdef CONFIG_KRETPROBE_ON_RETHOOK
-	rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler);
-	if (!rp->rh)
-		return -ENOMEM;
+	rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler,
+				sizeof(struct kretprobe_instance) +
+				rp->data_size, rp->maxactive);
+	if (IS_ERR(rp->rh))
+		return PTR_ERR(rp->rh);
 
-	for (i = 0; i < rp->maxactive; i++) {
-		inst = kzalloc(struct_size(inst, data, rp->data_size), GFP_KERNEL);
-		if (inst == NULL) {
-			rethook_free(rp->rh);
-			rp->rh = NULL;
-			return -ENOMEM;
-		}
-		rethook_add_node(rp->rh, &inst->node);
-	}
 	rp->nmissed = 0;
 	/* Establish function entry probe point */
 	ret = register_kprobe(&rp->kp);
···
 		rp->rh = NULL;
 	}
 #else	/* !CONFIG_KRETPROBE_ON_RETHOOK */
-	rp->freelist.head = NULL;
 	rp->rph = kzalloc(sizeof(struct kretprobe_holder), GFP_KERNEL);
 	if (!rp->rph)
 		return -ENOMEM;
 
-	rp->rph->rp = rp;
-	for (i = 0; i < rp->maxactive; i++) {
-		inst = kzalloc(struct_size(inst, data, rp->data_size), GFP_KERNEL);
-		if (inst == NULL) {
-			refcount_set(&rp->rph->ref, i);
-			free_rp_inst(rp);
-			return -ENOMEM;
-		}
-		inst->rph = rp->rph;
-		freelist_add(&inst->freelist, &rp->freelist);
+	if (objpool_init(&rp->rph->pool, rp->maxactive, rp->data_size +
+			sizeof(struct kretprobe_instance), GFP_KERNEL,
+			rp->rph, kretprobe_init_inst, kretprobe_fini_pool)) {
+		kfree(rp->rph);
+		rp->rph = NULL;
+		return -ENOMEM;
 	}
-	refcount_set(&rp->rph->ref, i);
-
+	rp->rph->rp = rp;
 	rp->nmissed = 0;
 	/* Establish function entry probe point */
 	ret = register_kprobe(&rp->kp);

kernel/trace/fprobe.c

···
 
 static int fprobe_init_rethook(struct fprobe *fp, int num)
 {
-	int i, size;
+	int size;
 
 	if (num <= 0)
 		return -EINVAL;
···
 	if (size <= 0)
 		return -EINVAL;
 
-	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
-	if (!fp->rethook)
-		return -ENOMEM;
-	for (i = 0; i < size; i++) {
-		struct fprobe_rethook_node *node;
+	/* Initialize rethook */
+	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler,
+				sizeof(struct fprobe_rethook_node), size);
+	if (IS_ERR(fp->rethook))
+		return PTR_ERR(fp->rethook);
 
-		node = kzalloc(sizeof(*node) + fp->entry_data_size, GFP_KERNEL);
-		if (!node) {
-			rethook_free(fp->rethook);
-			fp->rethook = NULL;
-			return -ENOMEM;
-		}
-		rethook_add_node(fp->rethook, &node->node);
-	}
 	return 0;
 }
 
 static void fprobe_fail_cleanup(struct fprobe *fp)
 {
-	if (fp->rethook) {
+	if (!IS_ERR_OR_NULL(fp->rethook)) {
 		/* Don't need to cleanup rethook->handler because this is not used. */
 		rethook_free(fp->rethook);
 		fp->rethook = NULL;
···
 	if (!fprobe_is_registered(fp))
 		return -EINVAL;
 
-	if (fp->rethook)
+	if (!IS_ERR_OR_NULL(fp->rethook))
 		rethook_stop(fp->rethook);
 
 	ret = unregister_ftrace_function(&fp->ops);
 	if (ret < 0)
 		return ret;
 
-	if (fp->rethook)
+	if (!IS_ERR_OR_NULL(fp->rethook))
 		rethook_free(fp->rethook);
 
 	ftrace_free_filter(&fp->ops);

kernel/trace/rethook.c

···
 #include <linux/preempt.h>
 #include <linux/rethook.h>
 #include <linux/slab.h>
-#include <linux/sort.h>
 
 /* Return hook list (shadow stack by list) */
 
···
 static void rethook_free_rcu(struct rcu_head *head)
 {
 	struct rethook *rh = container_of(head, struct rethook, rcu);
-	struct rethook_node *rhn;
-	struct freelist_node *node;
-	int count = 1;
-
-	node = rh->pool.head;
-	while (node) {
-		rhn = container_of(node, struct rethook_node, freelist);
-		node = node->next;
-		kfree(rhn);
-		count++;
-	}
-
-	/* The rh->ref is the number of pooled node + 1 */
-	if (refcount_sub_and_test(count, &rh->ref))
-		kfree(rh);
+	objpool_fini(&rh->pool);
 }
 
 /**
···
 	call_rcu(&rh->rcu, rethook_free_rcu);
 }
 
-/**
- * rethook_alloc() - Allocate struct rethook.
- * @data: a data to pass the @handler when hooking the return.
- * @handler: the return hook callback function.
- *
- * Allocate and initialize a new rethook with @data and @handler.
- * Return NULL if memory allocation fails or @handler is NULL.
- * Note that @handler == NULL means this rethook is going to be freed.
- */
-struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
+static int rethook_init_node(void *nod, void *context)
 {
-	struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);
+	struct rethook_node *node = nod;
 
-	if (!rh || !handler) {
-		kfree(rh);
-		return NULL;
-	}
+	node->rethook = context;
+	return 0;
+}
 
-	rh->data = data;
-	rh->handler = handler;
-	rh->pool.head = NULL;
-	refcount_set(&rh->ref, 1);
-
-	return rh;
+static int rethook_fini_pool(struct objpool_head *head, void *context)
+{
+	kfree(context);
+	return 0;
 }
 
 /**
- * rethook_add_node() - Add a new node to the rethook.
- * @rh: the struct rethook.
- * @node: the struct rethook_node to be added.
+ * rethook_alloc() - Allocate struct rethook.
+ * @data: a data to pass the @handler when hooking the return.
+ * @handler: the return hook callback function, must NOT be NULL
+ * @size: node size: rethook node and additional data
+ * @num: number of rethook nodes to be preallocated
  *
- * Add @node to @rh. User must allocate @node (as a part of user's
- * data structure.) The @node fields are initialized in this function.
+ * Allocate and initialize a new rethook with @data and @handler.
+ * Return pointer of new rethook, or error codes for failures.
+ *
+ * Note that @handler == NULL means this rethook is going to be freed.
  */
-void rethook_add_node(struct rethook *rh, struct rethook_node *node)
+struct rethook *rethook_alloc(void *data, rethook_handler_t handler,
+			      int size, int num)
 {
-	node->rethook = rh;
-	freelist_add(&node->freelist, &rh->pool);
-	refcount_inc(&rh->ref);
+	struct rethook *rh;
+
+	if (!handler || num <= 0 || size < sizeof(struct rethook_node))
+		return ERR_PTR(-EINVAL);
+
+	rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);
+	if (!rh)
+		return ERR_PTR(-ENOMEM);
+
+	rh->data = data;
+	rh->handler = handler;
+
+	/* initialize the objpool for rethook nodes */
+	if (objpool_init(&rh->pool, num, size, GFP_KERNEL, rh,
+			 rethook_init_node, rethook_fini_pool)) {
+		kfree(rh);
+		return ERR_PTR(-ENOMEM);
+	}
+	return rh;
 }
 
 static void free_rethook_node_rcu(struct rcu_head *head)
 {
 	struct rethook_node *node = container_of(head, struct rethook_node, rcu);
+	struct rethook *rh = node->rethook;
 
-	if (refcount_dec_and_test(&node->rethook->ref))
-		kfree(node->rethook);
-	kfree(node);
+	objpool_drop(node, &rh->pool);
 }
 
 /**
···
 	lockdep_assert_preemption_disabled();
 
 	if (likely(READ_ONCE(node->rethook->handler)))
-		freelist_add(&node->freelist, &node->rethook->pool);
+		objpool_push(node, &node->rethook->pool);
 	else
 		call_rcu(&node->rcu, free_rethook_node_rcu);
 }
···
 struct rethook_node *rethook_try_get(struct rethook *rh)
 {
 	rethook_handler_t handler = READ_ONCE(rh->handler);
-	struct freelist_node *fn;
 
 	lockdep_assert_preemption_disabled();
 
···
 	if (unlikely(!rcu_is_watching()))
 		return NULL;
 
-	fn = freelist_try_get(&rh->pool);
-	if (!fn)
-		return NULL;
-
-	return container_of(fn, struct rethook_node, freelist);
+	return (struct rethook_node *)objpool_pop(&rh->pool);
 }
 NOKPROBE_SYMBOL(rethook_try_get);
 

kernel/trace/trace_eprobe.c

···
 		name = trace_event_name(tp_event);
 		if (!name || strcmp(event_name, name))
 			continue;
-		if (!trace_event_try_get_ref(tp_event)) {
+		if (!trace_event_try_get_ref(tp_event))
 			return NULL;
-			break;
-		}
 		return tp_event;
-		break;
 	}
 	return NULL;
 }

lib/Kconfig.debug

···
 
 	  If unsure, say N.
 
+config TEST_OBJPOOL
+	tristate "Test module for correctness and stress of objpool"
+	default n
+	depends on m && DEBUG_KERNEL
+	help
+	  This builds the "test_objpool" module that should be used for
+	  correctness verification and concurrent testings of objects
+	  allocation and reclamation.
+
+	  If unsure, say N.
+
 endif # RUNTIME_TESTING_MENU
 
 config ARCH_USE_MEMTEST

lib/Makefile

···
 	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
 	 earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
 	 nmi_backtrace.o win_minmax.o memcat_p.o \
-	 buildid.o
+	 buildid.o objpool.o
 
 lib-$(CONFIG_PRINTK) += dump_stack.o
 lib-$(CONFIG_SMP) += cpumask.o
···
 obj-$(CONFIG_TEST_REF_TRACKER) += test_ref_tracker.o
 CFLAGS_test_fprobe.o += $(CC_FLAGS_FTRACE)
 obj-$(CONFIG_FPROBE_SANITY_TEST) += test_fprobe.o
+obj-$(CONFIG_TEST_OBJPOOL) += test_objpool.o
+
 #
 # CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
 # off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS

lib/objpool.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/objpool.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/atomic.h>
+#include <linux/irqflags.h>
+#include <linux/cpumask.h>
+#include <linux/log2.h>
+
+/*
+ * objpool: ring-array based lockless MPMC/FIFO queues
+ *
+ * Copyright: [e-mail],[e-mail]
+ */
+
+/* initialize percpu objpool_slot */
+static int
+objpool_init_percpu_slot(struct objpool_head *pool,
+			 struct objpool_slot *slot,
+			 int nodes, void *context,
+			 objpool_init_obj_cb objinit)
+{
+	void *obj = (void *)&slot->entries[pool->capacity];
+	int i;
+
+	/* initialize elements of percpu objpool_slot */
+	slot->mask = pool->capacity - 1;
+
+	for (i = 0; i < nodes; i++) {
+		if (objinit) {
+			int rc = objinit(obj, context);
+			if (rc)
+				return rc;
+		}
+		slot->entries[slot->tail & slot->mask] = obj;
+		obj = obj + pool->obj_size;
+		slot->tail++;
+		slot->last = slot->tail;
+		pool->nr_objs++;
+	}
+
+	return 0;
+}
+
+/* allocate and initialize percpu slots */
+static int
+objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
+			  void *context, objpool_init_obj_cb objinit)
+{
+	int i, cpu_count = 0;
+
+	for (i = 0; i < pool->nr_cpus; i++) {
+
+		struct objpool_slot *slot;
+		int nodes, size, rc;
+
+		/* skip the cpu node which could never be present */
+		if (!cpu_possible(i))
+			continue;
+
+		/* compute how many objects to be allocated with this slot */
+		nodes = nr_objs / num_possible_cpus();
+		if (cpu_count < (nr_objs % num_possible_cpus()))
+			nodes++;
+		cpu_count++;
+
+		size = struct_size(slot, entries, pool->capacity) +
+			pool->obj_size * nodes;
+
+		/*
+		 * here we allocate percpu-slot & objs together in a single
+		 * allocation to make it more compact, taking advantage of
+		 * warm caches and TLB hits. in default vmalloc is used to
+		 * reduce the pressure of kernel slab system. as we know,
+		 * mimimal size of vmalloc is one page since vmalloc would
+		 * always align the requested size to page size
+		 */
+		if (pool->gfp & GFP_ATOMIC)
+			slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
+		else
+			slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
+				cpu_to_node(i), __builtin_return_address(0));
+		if (!slot)
+			return -ENOMEM;
+		memset(slot, 0, size);
+		pool->cpu_slots[i] = slot;
+
+		/* initialize the objpool_slot of cpu node i */
+		rc = objpool_init_percpu_slot(pool, slot, nodes, context, objinit);
+		if (rc)
+			return rc;
+	}
+
+	return 0;
+}
+
+/* cleanup all percpu slots of the object pool */
+static void objpool_fini_percpu_slots(struct objpool_head *pool)
+{
+	int i;
+
+	if (!pool->cpu_slots)
+		return;
+
+	for (i = 0; i < pool->nr_cpus; i++)
+		kvfree(pool->cpu_slots[i]);
+	kfree(pool->cpu_slots);
+}
+
+/* initialize object pool and pre-allocate objects */
+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)
+{
+	int rc, capacity, slot_size;
+
+	/* check input parameters */
+	if (nr_objs <= 0 || nr_objs > OBJPOOL_NR_OBJECT_MAX ||
+	    object_size <= 0 || object_size > OBJPOOL_OBJECT_SIZE_MAX)
+		return -EINVAL;
+
+	/* align up to unsigned long size */
+	object_size = ALIGN(object_size, sizeof(long));
+
+	/* calculate capacity of percpu objpool_slot */
+	capacity = roundup_pow_of_two(nr_objs);
+	if (!capacity)
+		return -EINVAL;
+
+	/* initialize objpool pool */
+	memset(pool, 0, sizeof(struct objpool_head));
+	pool->nr_cpus = nr_cpu_ids;
+	pool->obj_size = object_size;
+	pool->capacity = capacity;
+	pool->gfp = gfp & ~__GFP_ZERO;
+	pool->context = context;
+	pool->release = release;
+	slot_size = pool->nr_cpus * sizeof(struct objpool_slot);
+	pool->cpu_slots = kzalloc(slot_size, pool->gfp);
+	if (!pool->cpu_slots)
+		return -ENOMEM;
+
+	/* initialize per-cpu slots */
+	rc = objpool_init_percpu_slots(pool, nr_objs, context, objinit);
+	if (rc)
+		objpool_fini_percpu_slots(pool);
+	else
+		refcount_set(&pool->ref, pool->nr_objs + 1);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(objpool_init);
+
+/* 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;
+}
+
+/* reclaim an object to object pool */
+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;
+}
+EXPORT_SYMBOL_GPL(objpool_push);
+
+/* 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;
+
+		/* 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;
+}
+
+/* allocate an object from object pool */
+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 < num_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;
+}
+EXPORT_SYMBOL_GPL(objpool_pop);
+
+/* release whole objpool forcely */
+void objpool_free(struct objpool_head *pool)
+{
+	if (!pool->cpu_slots)
+		return;
+
+	/* release percpu slots */
+	objpool_fini_percpu_slots(pool);
+
+	/* call user's cleanup callback if provided */
+	if (pool->release)
+		pool->release(pool, pool->context);
+}
+EXPORT_SYMBOL_GPL(objpool_free);
+
+/* drop the allocated object, rather reclaim it to objpool */
+int objpool_drop(void *obj, struct objpool_head *pool)
+{
+	if (!obj || !pool)
+		return -EINVAL;
+
+	if (refcount_dec_and_test(&pool->ref)) {
+		objpool_free(pool);
+		return 0;
+	}
+
+	return -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(objpool_drop);
+
+/* drop unused objects and defref objpool for releasing */
+void objpool_fini(struct objpool_head *pool)
+{
+	int count = 1; /* extra ref for objpool itself */
+
+	/* drop all remained objects from objpool */
+	while (objpool_pop(pool))
+		count++;
+
+	if (refcount_sub_and_test(count, &pool->ref))
+		objpool_free(pool);
+}
+EXPORT_SYMBOL_GPL(objpool_fini);

lib/test_objpool.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Test module for lockless object pool
+ *
+ * Copyright: [e-mail]
+ */
+
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/completion.h>
+#include <linux/kthread.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/delay.h>
+#include <linux/hrtimer.h>
+#include <linux/objpool.h>
+
+#define OT_NR_MAX_BULK (16)
+
+/* memory usage */
+struct ot_mem_stat {
+	atomic_long_t alloc;
+	atomic_long_t free;
+};
+
+/* object allocation results */
+struct ot_obj_stat {
+	unsigned long nhits;
+	unsigned long nmiss;
+};
+
+/* control & results per testcase */
+struct ot_data {
+	struct rw_semaphore start;
+	struct completion wait;
+	struct completion rcu;
+	atomic_t nthreads ____cacheline_aligned_in_smp;
+	atomic_t stop ____cacheline_aligned_in_smp;
+	struct ot_mem_stat kmalloc;
+	struct ot_mem_stat vmalloc;
+	struct ot_obj_stat objects;
+	u64    duration;
+};
+
+/* testcase */
+struct ot_test {
+	int async; /* synchronous or asynchronous */
+	int mode; /* only mode 0 supported */
+	int objsz; /* object size */
+	int duration; /* ms */
+	int delay; /* ms */
+	int bulk_normal;
+	int bulk_irq;
+	unsigned long hrtimer; /* ms */
+	const char *name;
+	struct ot_data data;
+};
+
+/* per-cpu worker */
+struct ot_item {
+	struct objpool_head *pool; /* pool head */
+	struct ot_test *test; /* test parameters */
+
+	void (*worker)(struct ot_item *item, int irq);
+
+	/* hrtimer control */
+	ktime_t hrtcycle;
+	struct hrtimer hrtimer;
+
+	int bulk[2]; /* for thread and irq */
+	int delay;
+	u32 niters;
+
+	/* summary per thread */
+	struct ot_obj_stat stat[2]; /* thread and irq */
+	u64 duration;
+};
+
+/*
+ * memory leakage checking
+ */
+
+static void *ot_kzalloc(struct ot_test *test, long size)
+{
+	void *ptr = kzalloc(size, GFP_KERNEL);
+
+	if (ptr)
+		atomic_long_add(size, &test->data.kmalloc.alloc);
+	return ptr;
+}
+
+static void ot_kfree(struct ot_test *test, void *ptr, long size)
+{
+	if (!ptr)
+		return;
+	atomic_long_add(size, &test->data.kmalloc.free);
+	kfree(ptr);
+}
+
+static void ot_mem_report(struct ot_test *test)
+{
+	long alloc, free;
+
+	pr_info("memory allocation summary for %s\n", test->name);
+
+	alloc = atomic_long_read(&test->data.kmalloc.alloc);
+	free = atomic_long_read(&test->data.kmalloc.free);
+	pr_info("  kmalloc: %lu - %lu = %lu\n", alloc, free, alloc - free);
+
+	alloc = atomic_long_read(&test->data.vmalloc.alloc);
+	free = atomic_long_read(&test->data.vmalloc.free);
+	pr_info("  vmalloc: %lu - %lu = %lu\n", alloc, free, alloc - free);
+}
+
+/* user object instance */
+struct ot_node {
+	void *owner;
+	unsigned long data;
+	unsigned long refs;
+	unsigned long payload[32];
+};
+
+/* user objpool manager */
+struct ot_context {
+	struct objpool_head pool; /* objpool head */
+	struct ot_test *test; /* test parameters */
+	void *ptr; /* user pool buffer */
+	unsigned long size; /* buffer size */
+	struct rcu_head rcu;
+};
+
+static DEFINE_PER_CPU(struct ot_item, ot_pcup_items);
+
+static int ot_init_data(struct ot_data *data)
+{
+	memset(data, 0, sizeof(*data));
+	init_rwsem(&data->start);
+	init_completion(&data->wait);
+	init_completion(&data->rcu);
+	atomic_set(&data->nthreads, 1);
+
+	return 0;
+}
+
+static int ot_init_node(void *nod, void *context)
+{
+	struct ot_context *sop = context;
+	struct ot_node *on = nod;
+
+	on->owner = &sop->pool;
+	return 0;
+}
+
+static enum hrtimer_restart ot_hrtimer_handler(struct hrtimer *hrt)
+{
+	struct ot_item *item = container_of(hrt, struct ot_item, hrtimer);
+	struct ot_test *test = item->test;
+
+	if (atomic_read_acquire(&test->data.stop))
+		return HRTIMER_NORESTART;
+
+	/* do bulk-testings for objects pop/push */
+	item->worker(item, 1);
+
+	hrtimer_forward(hrt, hrt->base->get_time(), item->hrtcycle);
+	return HRTIMER_RESTART;
+}
+
+static void ot_start_hrtimer(struct ot_item *item)
+{
+	if (!item->test->hrtimer)
+		return;
+	hrtimer_start(&item->hrtimer, item->hrtcycle, HRTIMER_MODE_REL);
+}
+
+static void ot_stop_hrtimer(struct ot_item *item)
+{
+	if (!item->test->hrtimer)
+		return;
+	hrtimer_cancel(&item->hrtimer);
+}
+
+static int ot_init_hrtimer(struct ot_item *item, unsigned long hrtimer)
+{
+	struct hrtimer *hrt = &item->hrtimer;
+
+	if (!hrtimer)
+		return -ENOENT;
+
+	item->hrtcycle = ktime_set(0, hrtimer * 1000000UL);
+	hrtimer_init(hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrt->function = ot_hrtimer_handler;
+	return 0;
+}
+
+static int ot_init_cpu_item(struct ot_item *item,
+			struct ot_test *test,
+			struct objpool_head *pool,
+			void (*worker)(struct ot_item *, int))
+{
+	memset(item, 0, sizeof(*item));
+	item->pool = pool;
+	item->test = test;
+	item->worker = worker;
+
+	item->bulk[0] = test->bulk_normal;
+	item->bulk[1] = test->bulk_irq;
+	item->delay = test->delay;
+
+	/* initialize hrtimer */
+	ot_init_hrtimer(item, item->test->hrtimer);
+	return 0;
+}
+
+static int ot_thread_worker(void *arg)
+{
+	struct ot_item *item = arg;
+	struct ot_test *test = item->test;
+	ktime_t start;
+
+	atomic_inc(&test->data.nthreads);
+	down_read(&test->data.start);
+	up_read(&test->data.start);
+	start = ktime_get();
+	ot_start_hrtimer(item);
+	do {
+		if (atomic_read_acquire(&test->data.stop))
+			break;
+		/* do bulk-testings for objects pop/push */
+		item->worker(item, 0);
+	} while (!kthread_should_stop());
+	ot_stop_hrtimer(item);
+	item->duration = (u64) ktime_us_delta(ktime_get(), start);
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	return 0;
+}
+
+static void ot_perf_report(struct ot_test *test, u64 duration)
+{
+	struct ot_obj_stat total, normal = {0}, irq = {0};
+	int cpu, nthreads = 0;
+
+	pr_info("\n");
+	pr_info("Testing summary for %s\n", test->name);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		if (!item->duration)
+			continue;
+		normal.nhits += item->stat[0].nhits;
+		normal.nmiss += item->stat[0].nmiss;
+		irq.nhits += item->stat[1].nhits;
+		irq.nmiss += item->stat[1].nmiss;
+		pr_info("CPU: %d  duration: %lluus\n", cpu, item->duration);
+		pr_info("\tthread:\t%16lu hits \t%16lu miss\n",
+			item->stat[0].nhits, item->stat[0].nmiss);
+		pr_info("\tirq:   \t%16lu hits \t%16lu miss\n",
+			item->stat[1].nhits, item->stat[1].nmiss);
+		pr_info("\ttotal: \t%16lu hits \t%16lu miss\n",
+			item->stat[0].nhits + item->stat[1].nhits,
+			item->stat[0].nmiss + item->stat[1].nmiss);
+		nthreads++;
+	}
+
+	total.nhits = normal.nhits + irq.nhits;
+	total.nmiss = normal.nmiss + irq.nmiss;
+
+	pr_info("ALL: \tnthreads: %d  duration: %lluus\n", nthreads, duration);
+	pr_info("SUM: \t%16lu hits \t%16lu miss\n",
+		total.nhits, total.nmiss);
+
+	test->data.objects = total;
+	test->data.duration = duration;
+}
+
+/*
+ * synchronous test cases for objpool manipulation
+ */
+
+/* objpool manipulation for synchronous mode (percpu objpool) */
+static struct ot_context *ot_init_sync_m0(struct ot_test *test)
+{
+	struct ot_context *sop = NULL;
+	int max = num_possible_cpus() << 3;
+	gfp_t gfp = GFP_KERNEL;
+
+	sop = (struct ot_context *)ot_kzalloc(test, sizeof(*sop));
+	if (!sop)
+		return NULL;
+	sop->test = test;
+	if (test->objsz < 512)
+		gfp = GFP_ATOMIC;
+
+	if (objpool_init(&sop->pool, max, test->objsz,
+			 gfp, sop, ot_init_node, NULL)) {
+		ot_kfree(test, sop, sizeof(*sop));
+		return NULL;
+	}
+	WARN_ON(max != sop->pool.nr_objs);
+
+	return sop;
+}
+
+static void ot_fini_sync(struct ot_context *sop)
+{
+	objpool_fini(&sop->pool);
+	ot_kfree(sop->test, sop, sizeof(*sop));
+}
+
+struct {
+	struct ot_context * (*init)(struct ot_test *oc);
+	void (*fini)(struct ot_context *sop);
+} g_ot_sync_ops[] = {
+	{.init = ot_init_sync_m0, .fini = ot_fini_sync},
+};
+
+/*
+ * synchronous test cases: performance mode
+ */
+
+static void ot_bulk_sync(struct ot_item *item, int irq)
+{
+	struct ot_node *nods[OT_NR_MAX_BULK];
+	int i;
+
+	for (i = 0; i < item->bulk[irq]; i++)
+		nods[i] = objpool_pop(item->pool);
+
+	if (!irq && (item->delay || !(++(item->niters) & 0x7FFF)))
+		msleep(item->delay);
+
+	while (i-- > 0) {
+		struct ot_node *on = nods[i];
+		if (on) {
+			on->refs++;
+			objpool_push(on, item->pool);
+			item->stat[irq].nhits++;
+		} else {
+			item->stat[irq].nmiss++;
+		}
+	}
+}
+
+static int ot_start_sync(struct ot_test *test)
+{
+	struct ot_context *sop;
+	ktime_t start;
+	u64 duration;
+	unsigned long timeout;
+	int cpu;
+
+	/* initialize objpool for syncrhonous testcase */
+	sop = g_ot_sync_ops[test->mode].init(test);
+	if (!sop)
+		return -ENOMEM;
+
+	/* grab rwsem to block testing threads */
+	down_write(&test->data.start);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		struct task_struct *work;
+
+		ot_init_cpu_item(item, test, &sop->pool, ot_bulk_sync);
+
+		/* skip offline cpus */
+		if (!cpu_online(cpu))
+			continue;
+
+		work = kthread_create_on_node(ot_thread_worker, item,
+				cpu_to_node(cpu), "ot_worker_%d", cpu);
+		if (IS_ERR(work)) {
+			pr_err("failed to create thread for cpu %d\n", cpu);
+		} else {
+			kthread_bind(work, cpu);
+			wake_up_process(work);
+		}
+	}
+
+	/* wait a while to make sure all threads waiting at start line */
+	msleep(20);
+
+	/* in case no threads were created: memory insufficient ? */
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	// sched_set_fifo_low(current);
+
+	/* start objpool testing threads */
+	start = ktime_get();
+	up_write(&test->data.start);
+
+	/* yeild cpu to worker threads for duration ms */
+	timeout = msecs_to_jiffies(test->duration);
+	schedule_timeout_interruptible(timeout);
+
+	/* tell workers threads to quit */
+	atomic_set_release(&test->data.stop, 1);
+
+	/* wait all workers threads finish and quit */
+	wait_for_completion(&test->data.wait);
+	duration = (u64) ktime_us_delta(ktime_get(), start);
+
+	/* cleanup objpool */
+	g_ot_sync_ops[test->mode].fini(sop);
+
+	/* report testing summary and performance results */
+	ot_perf_report(test, duration);
+
+	/* report memory allocation summary */
+	ot_mem_report(test);
+
+	return 0;
+}
+
+/*
+ * asynchronous test cases: pool lifecycle controlled by refcount
+ */
+
+static void ot_fini_async_rcu(struct rcu_head *rcu)
+{
+	struct ot_context *sop = container_of(rcu, struct ot_context, rcu);
+	struct ot_test *test = sop->test;
+
+	/* here all cpus are aware of the stop event: test->data.stop = 1 */
+	WARN_ON(!atomic_read_acquire(&test->data.stop));
+
+	objpool_fini(&sop->pool);
+	complete(&test->data.rcu);
+}
+
+static void ot_fini_async(struct ot_context *sop)
+{
+	/* make sure the stop event is acknowledged by all cores */
+	call_rcu(&sop->rcu, ot_fini_async_rcu);
+}
+
+static int ot_objpool_release(struct objpool_head *head, void *context)
+{
+	struct ot_context *sop = context;
+
+	WARN_ON(!head || !sop || head != &sop->pool);
+
+	/* do context cleaning if needed */
+	if (sop)
+		ot_kfree(sop->test, sop, sizeof(*sop));
+
+	return 0;
+}
+
+static struct ot_context *ot_init_async_m0(struct ot_test *test)
+{
+	struct ot_context *sop = NULL;
+	int max = num_possible_cpus() << 3;
+	gfp_t gfp = GFP_KERNEL;
+
+	sop = (struct ot_context *)ot_kzalloc(test, sizeof(*sop));
+	if (!sop)
+		return NULL;
+	sop->test = test;
+	if (test->objsz < 512)
+		gfp = GFP_ATOMIC;
+
+	if (objpool_init(&sop->pool, max, test->objsz, gfp, sop,
+			 ot_init_node, ot_objpool_release)) {
+		ot_kfree(test, sop, sizeof(*sop));
+		return NULL;
+	}
+	WARN_ON(max != sop->pool.nr_objs);
+
+	return sop;
+}
+
+struct {
+	struct ot_context * (*init)(struct ot_test *oc);
+	void (*fini)(struct ot_context *sop);
+} g_ot_async_ops[] = {
+	{.init = ot_init_async_m0, .fini = ot_fini_async},
+};
+
+static void ot_nod_recycle(struct ot_node *on, struct objpool_head *pool,
+			int release)
+{
+	struct ot_context *sop;
+
+	on->refs++;
+
+	if (!release) {
+		/* push object back to opjpool for reuse */
+		objpool_push(on, pool);
+		return;
+	}
+
+	sop = container_of(pool, struct ot_context, pool);
+	WARN_ON(sop != pool->context);
+
+	/* unref objpool with nod removed forever */
+	objpool_drop(on, pool);
+}
+
+static void ot_bulk_async(struct ot_item *item, int irq)
+{
+	struct ot_test *test = item->test;
+	struct ot_node *nods[OT_NR_MAX_BULK];
+	int i, stop;
+
+	for (i = 0; i < item->bulk[irq]; i++)
+		nods[i] = objpool_pop(item->pool);
+
+	if (!irq) {
+		if (item->delay || !(++(item->niters) & 0x7FFF))
+			msleep(item->delay);
+		get_cpu();
+	}
+
+	stop = atomic_read_acquire(&test->data.stop);
+
+	/* drop all objects and deref objpool */
+	while (i-- > 0) {
+		struct ot_node *on = nods[i];
+
+		if (on) {
+			on->refs++;
+			ot_nod_recycle(on, item->pool, stop);
+			item->stat[irq].nhits++;
+		} else {
+			item->stat[irq].nmiss++;
+		}
+	}
+
+	if (!irq)
+		put_cpu();
+}
+
+static int ot_start_async(struct ot_test *test)
+{
+	struct ot_context *sop;
+	ktime_t start;
+	u64 duration;
+	unsigned long timeout;
+	int cpu;
+
+	/* initialize objpool for syncrhonous testcase */
+	sop = g_ot_async_ops[test->mode].init(test);
+	if (!sop)
+		return -ENOMEM;
+
+	/* grab rwsem to block testing threads */
+	down_write(&test->data.start);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		struct task_struct *work;
+
+		ot_init_cpu_item(item, test, &sop->pool, ot_bulk_async);
+
+		/* skip offline cpus */
+		if (!cpu_online(cpu))
+			continue;
+
+		work = kthread_create_on_node(ot_thread_worker, item,
+				cpu_to_node(cpu), "ot_worker_%d", cpu);
+		if (IS_ERR(work)) {
+			pr_err("failed to create thread for cpu %d\n", cpu);
+		} else {
+			kthread_bind(work, cpu);
+			wake_up_process(work);
+		}
+	}
+
+	/* wait a while to make sure all threads waiting at start line */
+	msleep(20);
+
+	/* in case no threads were created: memory insufficient ? */
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	/* start objpool testing threads */
+	start = ktime_get();
+	up_write(&test->data.start);
+
+	/* yeild cpu to worker threads for duration ms */
+	timeout = msecs_to_jiffies(test->duration);
+	schedule_timeout_interruptible(timeout);
+
+	/* tell workers threads to quit */
+	atomic_set_release(&test->data.stop, 1);
+
+	/* do async-finalization */
+	g_ot_async_ops[test->mode].fini(sop);
+
+	/* wait all workers threads finish and quit */
+	wait_for_completion(&test->data.wait);
+	duration = (u64) ktime_us_delta(ktime_get(), start);
+
+	/* assure rcu callback is triggered */
+	wait_for_completion(&test->data.rcu);
+
+	/*
+	 * now we are sure that objpool is finalized either
+	 * by rcu callback or by worker threads
+	 */
+
+	/* report testing summary and performance results */
+	ot_perf_report(test, duration);
+
+	/* report memory allocation summary */
+	ot_mem_report(test);
+
+	return 0;
+}
+
+/*
+ * predefined testing cases:
+ *   synchronous case / overrun case / async case
+ *
+ * async: synchronous or asynchronous testing
+ * mode: only mode 0 supported
+ * objsz: object size
+ * duration: int, total test time in ms
+ * delay: int, delay (in ms) between each iteration
+ * bulk_normal: int, repeat times for thread worker
+ * bulk_irq: int, repeat times for irq consumer
+ * hrtimer: unsigned long, hrtimer intervnal in ms
+ * name: char *, tag for current test ot_item
+ */
+
+#define NODE_COMPACT sizeof(struct ot_node)
+#define NODE_VMALLOC (512)
+
+struct ot_test g_testcases[] = {
+
+	/* sync & normal */
+	{0, 0, NODE_COMPACT, 1000, 0,  1,  0,  0, "sync: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0,  1,  0,  0, "sync: percpu objpool from vmalloc"},
+
+	/* sync & hrtimer */
+	{0, 0, NODE_COMPACT, 1000, 0,  1,  1,  4, "sync & hrtimer: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0,  1,  1,  4, "sync & hrtimer: percpu objpool from vmalloc"},
+
+	/* sync & overrun */
+	{0, 0, NODE_COMPACT, 1000, 0, 16,  0,  0, "sync overrun: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0, 16,  0,  0, "sync overrun: percpu objpool from vmalloc"},
+
+	/* async mode */
+	{1, 0, NODE_COMPACT, 1000, 100,  1,  0,  0, "async: percpu objpool"},
+	{1, 0, NODE_VMALLOC, 1000, 100,  1,  0,  0, "async: percpu objpool from vmalloc"},
+
+	/* async + hrtimer mode */
+	{1, 0, NODE_COMPACT, 1000, 0,  4,  4,  4, "async & hrtimer: percpu objpool"},
+	{1, 0, NODE_VMALLOC, 1000, 0,  4,  4,  4, "async & hrtimer: percpu objpool from vmalloc"},
+};
+
+static int __init ot_mod_init(void)
+{
+	int i;
+
+	/* perform testings */
+	for (i = 0; i < ARRAY_SIZE(g_testcases); i++) {
+		ot_init_data(&g_testcases[i].data);
+		if (g_testcases[i].async)
+			ot_start_async(&g_testcases[i]);
+		else
+			ot_start_sync(&g_testcases[i]);
+	}
+
+	/* show tests summary */
+	pr_info("\n");
+	pr_info("Summary of testcases:\n");
+	for (i = 0; i < ARRAY_SIZE(g_testcases); i++) {
+		pr_info("    duration: %lluus \thits: %10lu \tmiss: %10lu \t%s\n",
+			g_testcases[i].data.duration, g_testcases[i].data.objects.nhits,
+			g_testcases[i].data.objects.nmiss, g_testcases[i].name);
+	}
+
+	return -EAGAIN;
+}
+
+static void __exit ot_mod_exit(void)
+{
+}
+
+module_init(ot_mod_init);
+module_exit(ot_mod_exit);
+
+MODULE_LICENSE("GPL");

samples/kprobes/kretprobe_example.c

···
 	ktime_t entry_stamp;
 };
 
-/* Here we use the entry_hanlder to timestamp function entry */
+/* Here we use the entry_handler to timestamp function entry */
 static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
 {
 	struct my_data *data;