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d1f652f8 MD |
1 | /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1) |
2 | * | |
3 | * lttng-tracker-pid.c | |
4 | * | |
5 | * LTTng Process ID tracking. | |
6 | * | |
7 | * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
8 | */ | |
9 | ||
10 | #include <linux/module.h> | |
11 | #include <linux/slab.h> | |
12 | #include <linux/err.h> | |
13 | #include <linux/seq_file.h> | |
14 | #include <linux/stringify.h> | |
15 | #include <linux/hash.h> | |
16 | #include <linux/rcupdate.h> | |
17 | ||
18 | #include <wrapper/tracepoint.h> | |
19 | #include <wrapper/rcu.h> | |
20 | #include <wrapper/list.h> | |
21 | #include <lttng-events.h> | |
22 | ||
23 | /* | |
24 | * Hash table is allocated and freed when there are no possible | |
25 | * concurrent lookups (ensured by the alloc/free caller). However, | |
26 | * there can be concurrent RCU lookups vs add/del operations. | |
27 | * | |
28 | * Concurrent updates of the PID hash table are forbidden: the caller | |
29 | * must ensure mutual exclusion. This is currently done by holding the | |
30 | * sessions_mutex across calls to create, destroy, add, and del | |
31 | * functions of this API. | |
32 | */ | |
33 | int lttng_id_tracker_get_node_id(const struct lttng_id_hash_node *node) | |
34 | { | |
35 | return node->id; | |
36 | } | |
37 | ||
38 | /* | |
39 | * Lookup performed from RCU read-side critical section (RCU sched), | |
40 | * protected by preemption off at the tracepoint call site. | |
41 | * Return true if found, false if not found. | |
42 | */ | |
43 | bool lttng_id_tracker_lookup(struct lttng_id_tracker_rcu *p, int id) | |
44 | { | |
45 | struct hlist_head *head; | |
46 | struct lttng_id_hash_node *e; | |
47 | uint32_t hash = hash_32(id, 32); | |
48 | ||
49 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; | |
50 | lttng_hlist_for_each_entry_rcu(e, head, hlist) { | |
51 | if (id == e->id) | |
52 | return true; /* Found */ | |
53 | } | |
54 | return false; | |
55 | } | |
56 | EXPORT_SYMBOL_GPL(lttng_id_tracker_lookup); | |
57 | ||
58 | static struct lttng_id_tracker_rcu *lttng_id_tracker_rcu_create(void) | |
59 | { | |
60 | struct lttng_id_tracker_rcu *tracker; | |
61 | ||
62 | tracker = kzalloc(sizeof(struct lttng_id_tracker_rcu), GFP_KERNEL); | |
63 | if (!tracker) | |
64 | return NULL; | |
65 | return tracker; | |
66 | } | |
67 | ||
68 | /* | |
69 | * Tracker add and del operations support concurrent RCU lookups. | |
70 | */ | |
71 | int lttng_id_tracker_add(struct lttng_id_tracker *lf, int id) | |
72 | { | |
73 | struct hlist_head *head; | |
74 | struct lttng_id_hash_node *e; | |
75 | struct lttng_id_tracker_rcu *p = lf->p; | |
76 | uint32_t hash = hash_32(id, 32); | |
77 | bool allocated = false; | |
f59ab559 | 78 | int ret; |
d1f652f8 MD |
79 | |
80 | if (!p) { | |
81 | p = lttng_id_tracker_rcu_create(); | |
82 | if (!p) | |
83 | return -ENOMEM; | |
84 | allocated = true; | |
85 | } | |
86 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; | |
87 | lttng_hlist_for_each_entry(e, head, hlist) { | |
f59ab559 MD |
88 | if (id == e->id) { |
89 | ret = -EEXIST; | |
90 | goto error; | |
91 | } | |
d1f652f8 MD |
92 | } |
93 | e = kmalloc(sizeof(struct lttng_id_hash_node), GFP_KERNEL); | |
f59ab559 MD |
94 | if (!e) { |
95 | ret = -ENOMEM; | |
96 | goto error; | |
97 | } | |
d1f652f8 MD |
98 | e->id = id; |
99 | hlist_add_head_rcu(&e->hlist, head); | |
100 | if (allocated) { | |
101 | rcu_assign_pointer(lf->p, p); | |
102 | } | |
103 | return 0; | |
f59ab559 MD |
104 | |
105 | error: | |
106 | if (allocated) { | |
107 | kfree(p); | |
108 | } | |
109 | return ret; | |
d1f652f8 MD |
110 | } |
111 | ||
112 | static | |
113 | void id_tracker_del_node_rcu(struct lttng_id_hash_node *e) | |
114 | { | |
115 | hlist_del_rcu(&e->hlist); | |
116 | /* | |
117 | * We choose to use a heavyweight synchronize on removal here, | |
118 | * since removal of an ID from the tracker mask is a rare | |
119 | * operation, and we don't want to use more cache lines than | |
120 | * what we really need when doing the ID lookups, so we don't | |
121 | * want to afford adding a rcu_head field to those pid hash | |
122 | * node. | |
123 | */ | |
124 | synchronize_trace(); | |
125 | kfree(e); | |
126 | } | |
127 | ||
128 | /* | |
129 | * This removal is only used on destroy, so it does not need to support | |
130 | * concurrent RCU lookups. | |
131 | */ | |
132 | static | |
133 | void id_tracker_del_node(struct lttng_id_hash_node *e) | |
134 | { | |
135 | hlist_del(&e->hlist); | |
136 | kfree(e); | |
137 | } | |
138 | ||
139 | int lttng_id_tracker_del(struct lttng_id_tracker *lf, int id) | |
140 | { | |
141 | struct hlist_head *head; | |
142 | struct lttng_id_hash_node *e; | |
143 | struct lttng_id_tracker_rcu *p = lf->p; | |
144 | uint32_t hash = hash_32(id, 32); | |
145 | ||
146 | if (!p) | |
147 | return -ENOENT; | |
148 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; | |
149 | /* | |
150 | * No need of _safe iteration, because we stop traversal as soon | |
151 | * as we remove the entry. | |
152 | */ | |
153 | lttng_hlist_for_each_entry(e, head, hlist) { | |
154 | if (id == e->id) { | |
155 | id_tracker_del_node_rcu(e); | |
156 | return 0; | |
157 | } | |
158 | } | |
159 | return -ENOENT; /* Not found */ | |
160 | } | |
161 | ||
162 | static void lttng_id_tracker_rcu_destroy(struct lttng_id_tracker_rcu *p) | |
163 | { | |
164 | int i; | |
165 | ||
166 | if (!p) | |
167 | return; | |
168 | for (i = 0; i < LTTNG_ID_TABLE_SIZE; i++) { | |
169 | struct hlist_head *head = &p->id_hash[i]; | |
170 | struct lttng_id_hash_node *e; | |
171 | struct hlist_node *tmp; | |
172 | ||
173 | lttng_hlist_for_each_entry_safe(e, tmp, head, hlist) | |
174 | id_tracker_del_node(e); | |
175 | } | |
176 | kfree(p); | |
177 | } | |
178 | ||
179 | int lttng_id_tracker_empty_set(struct lttng_id_tracker *lf) | |
180 | { | |
181 | struct lttng_id_tracker_rcu *p, *oldp; | |
182 | ||
183 | p = lttng_id_tracker_rcu_create(); | |
184 | if (!p) | |
185 | return -ENOMEM; | |
186 | oldp = lf->p; | |
187 | rcu_assign_pointer(lf->p, p); | |
188 | synchronize_trace(); | |
189 | lttng_id_tracker_rcu_destroy(oldp); | |
190 | return 0; | |
191 | } | |
192 | ||
193 | void lttng_id_tracker_destroy(struct lttng_id_tracker *lf, bool rcu) | |
194 | { | |
195 | struct lttng_id_tracker_rcu *p = lf->p; | |
196 | ||
197 | if (!lf->p) | |
198 | return; | |
199 | rcu_assign_pointer(lf->p, NULL); | |
200 | if (rcu) | |
201 | synchronize_trace(); | |
202 | lttng_id_tracker_rcu_destroy(p); | |
203 | } |