xref: /linux/kernel/bpf/percpu_freelist.c (revision 7ae9fb1b7ecbb5d85d07857943f677fd1a559b18)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /* Copyright (c) 2016 Facebook
3  */
4 #include "percpu_freelist.h"
5 
pcpu_freelist_init(struct pcpu_freelist * s)6 int pcpu_freelist_init(struct pcpu_freelist *s)
7 {
8 	int cpu;
9 
10 	s->freelist = alloc_percpu(struct pcpu_freelist_head);
11 	if (!s->freelist)
12 		return -ENOMEM;
13 
14 	for_each_possible_cpu(cpu) {
15 		struct pcpu_freelist_head *head = per_cpu_ptr(s->freelist, cpu);
16 
17 		raw_spin_lock_init(&head->lock);
18 		head->first = NULL;
19 	}
20 	raw_spin_lock_init(&s->extralist.lock);
21 	s->extralist.first = NULL;
22 	return 0;
23 }
24 
pcpu_freelist_destroy(struct pcpu_freelist * s)25 void pcpu_freelist_destroy(struct pcpu_freelist *s)
26 {
27 	free_percpu(s->freelist);
28 }
29 
pcpu_freelist_push_node(struct pcpu_freelist_head * head,struct pcpu_freelist_node * node)30 static inline void pcpu_freelist_push_node(struct pcpu_freelist_head *head,
31 					   struct pcpu_freelist_node *node)
32 {
33 	node->next = head->first;
34 	WRITE_ONCE(head->first, node);
35 }
36 
___pcpu_freelist_push(struct pcpu_freelist_head * head,struct pcpu_freelist_node * node)37 static inline void ___pcpu_freelist_push(struct pcpu_freelist_head *head,
38 					 struct pcpu_freelist_node *node)
39 {
40 	raw_spin_lock(&head->lock);
41 	pcpu_freelist_push_node(head, node);
42 	raw_spin_unlock(&head->lock);
43 }
44 
pcpu_freelist_try_push_extra(struct pcpu_freelist * s,struct pcpu_freelist_node * node)45 static inline bool pcpu_freelist_try_push_extra(struct pcpu_freelist *s,
46 						struct pcpu_freelist_node *node)
47 {
48 	if (!raw_spin_trylock(&s->extralist.lock))
49 		return false;
50 
51 	pcpu_freelist_push_node(&s->extralist, node);
52 	raw_spin_unlock(&s->extralist.lock);
53 	return true;
54 }
55 
___pcpu_freelist_push_nmi(struct pcpu_freelist * s,struct pcpu_freelist_node * node)56 static inline void ___pcpu_freelist_push_nmi(struct pcpu_freelist *s,
57 					     struct pcpu_freelist_node *node)
58 {
59 	int cpu, orig_cpu;
60 
61 	orig_cpu = raw_smp_processor_id();
62 	while (1) {
63 		for_each_cpu_wrap(cpu, cpu_possible_mask, orig_cpu) {
64 			struct pcpu_freelist_head *head;
65 
66 			head = per_cpu_ptr(s->freelist, cpu);
67 			if (raw_spin_trylock(&head->lock)) {
68 				pcpu_freelist_push_node(head, node);
69 				raw_spin_unlock(&head->lock);
70 				return;
71 			}
72 		}
73 
74 		/* cannot lock any per cpu lock, try extralist */
75 		if (pcpu_freelist_try_push_extra(s, node))
76 			return;
77 	}
78 }
79 
__pcpu_freelist_push(struct pcpu_freelist * s,struct pcpu_freelist_node * node)80 void __pcpu_freelist_push(struct pcpu_freelist *s,
81 			struct pcpu_freelist_node *node)
82 {
83 	if (in_nmi())
84 		___pcpu_freelist_push_nmi(s, node);
85 	else
86 		___pcpu_freelist_push(this_cpu_ptr(s->freelist), node);
87 }
88 
pcpu_freelist_push(struct pcpu_freelist * s,struct pcpu_freelist_node * node)89 void pcpu_freelist_push(struct pcpu_freelist *s,
90 			struct pcpu_freelist_node *node)
91 {
92 	unsigned long flags;
93 
94 	local_irq_save(flags);
95 	__pcpu_freelist_push(s, node);
96 	local_irq_restore(flags);
97 }
98 
pcpu_freelist_populate(struct pcpu_freelist * s,void * buf,u32 elem_size,u32 nr_elems)99 void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
100 			    u32 nr_elems)
101 {
102 	struct pcpu_freelist_head *head;
103 	unsigned int cpu, cpu_idx, i, j, n, m;
104 
105 	n = nr_elems / num_possible_cpus();
106 	m = nr_elems % num_possible_cpus();
107 
108 	cpu_idx = 0;
109 	for_each_possible_cpu(cpu) {
110 		head = per_cpu_ptr(s->freelist, cpu);
111 		j = n + (cpu_idx < m ? 1 : 0);
112 		for (i = 0; i < j; i++) {
113 			/* No locking required as this is not visible yet. */
114 			pcpu_freelist_push_node(head, buf);
115 			buf += elem_size;
116 		}
117 		cpu_idx++;
118 	}
119 }
120 
___pcpu_freelist_pop(struct pcpu_freelist * s)121 static struct pcpu_freelist_node *___pcpu_freelist_pop(struct pcpu_freelist *s)
122 {
123 	struct pcpu_freelist_head *head;
124 	struct pcpu_freelist_node *node;
125 	int cpu;
126 
127 	for_each_cpu_wrap(cpu, cpu_possible_mask, raw_smp_processor_id()) {
128 		head = per_cpu_ptr(s->freelist, cpu);
129 		if (!READ_ONCE(head->first))
130 			continue;
131 		raw_spin_lock(&head->lock);
132 		node = head->first;
133 		if (node) {
134 			WRITE_ONCE(head->first, node->next);
135 			raw_spin_unlock(&head->lock);
136 			return node;
137 		}
138 		raw_spin_unlock(&head->lock);
139 	}
140 
141 	/* per cpu lists are all empty, try extralist */
142 	if (!READ_ONCE(s->extralist.first))
143 		return NULL;
144 	raw_spin_lock(&s->extralist.lock);
145 	node = s->extralist.first;
146 	if (node)
147 		WRITE_ONCE(s->extralist.first, node->next);
148 	raw_spin_unlock(&s->extralist.lock);
149 	return node;
150 }
151 
152 static struct pcpu_freelist_node *
___pcpu_freelist_pop_nmi(struct pcpu_freelist * s)153 ___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
154 {
155 	struct pcpu_freelist_head *head;
156 	struct pcpu_freelist_node *node;
157 	int cpu;
158 
159 	for_each_cpu_wrap(cpu, cpu_possible_mask, raw_smp_processor_id()) {
160 		head = per_cpu_ptr(s->freelist, cpu);
161 		if (!READ_ONCE(head->first))
162 			continue;
163 		if (raw_spin_trylock(&head->lock)) {
164 			node = head->first;
165 			if (node) {
166 				WRITE_ONCE(head->first, node->next);
167 				raw_spin_unlock(&head->lock);
168 				return node;
169 			}
170 			raw_spin_unlock(&head->lock);
171 		}
172 	}
173 
174 	/* cannot pop from per cpu lists, try extralist */
175 	if (!READ_ONCE(s->extralist.first) || !raw_spin_trylock(&s->extralist.lock))
176 		return NULL;
177 	node = s->extralist.first;
178 	if (node)
179 		WRITE_ONCE(s->extralist.first, node->next);
180 	raw_spin_unlock(&s->extralist.lock);
181 	return node;
182 }
183 
__pcpu_freelist_pop(struct pcpu_freelist * s)184 struct pcpu_freelist_node *__pcpu_freelist_pop(struct pcpu_freelist *s)
185 {
186 	if (in_nmi())
187 		return ___pcpu_freelist_pop_nmi(s);
188 	return ___pcpu_freelist_pop(s);
189 }
190 
pcpu_freelist_pop(struct pcpu_freelist * s)191 struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
192 {
193 	struct pcpu_freelist_node *ret;
194 	unsigned long flags;
195 
196 	local_irq_save(flags);
197 	ret = __pcpu_freelist_pop(s);
198 	local_irq_restore(flags);
199 	return ret;
200 }
201