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b7cdc182 | 1 | /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only) |
d1f652f8 MD |
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 | ||
d1f652f8 MD |
18 | #include <lttng-events.h> |
19 | ||
20 | /* | |
21 | * Hash table is allocated and freed when there are no possible | |
22 | * concurrent lookups (ensured by the alloc/free caller). However, | |
23 | * there can be concurrent RCU lookups vs add/del operations. | |
24 | * | |
25 | * Concurrent updates of the PID hash table are forbidden: the caller | |
26 | * must ensure mutual exclusion. This is currently done by holding the | |
27 | * sessions_mutex across calls to create, destroy, add, and del | |
28 | * functions of this API. | |
29 | */ | |
30 | int lttng_id_tracker_get_node_id(const struct lttng_id_hash_node *node) | |
31 | { | |
32 | return node->id; | |
33 | } | |
34 | ||
35 | /* | |
36 | * Lookup performed from RCU read-side critical section (RCU sched), | |
37 | * protected by preemption off at the tracepoint call site. | |
38 | * Return true if found, false if not found. | |
39 | */ | |
40 | bool lttng_id_tracker_lookup(struct lttng_id_tracker_rcu *p, int id) | |
41 | { | |
42 | struct hlist_head *head; | |
43 | struct lttng_id_hash_node *e; | |
44 | uint32_t hash = hash_32(id, 32); | |
45 | ||
46 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; | |
3bc8535a | 47 | hlist_for_each_entry_rcu_notrace(e, head, hlist) { |
d1f652f8 MD |
48 | if (id == e->id) |
49 | return true; /* Found */ | |
50 | } | |
51 | return false; | |
52 | } | |
53 | EXPORT_SYMBOL_GPL(lttng_id_tracker_lookup); | |
54 | ||
55 | static struct lttng_id_tracker_rcu *lttng_id_tracker_rcu_create(void) | |
56 | { | |
57 | struct lttng_id_tracker_rcu *tracker; | |
58 | ||
59 | tracker = kzalloc(sizeof(struct lttng_id_tracker_rcu), GFP_KERNEL); | |
60 | if (!tracker) | |
61 | return NULL; | |
62 | return tracker; | |
63 | } | |
64 | ||
65 | /* | |
66 | * Tracker add and del operations support concurrent RCU lookups. | |
67 | */ | |
68 | int lttng_id_tracker_add(struct lttng_id_tracker *lf, int id) | |
69 | { | |
70 | struct hlist_head *head; | |
71 | struct lttng_id_hash_node *e; | |
72 | struct lttng_id_tracker_rcu *p = lf->p; | |
73 | uint32_t hash = hash_32(id, 32); | |
74 | bool allocated = false; | |
75 | ||
76 | if (!p) { | |
77 | p = lttng_id_tracker_rcu_create(); | |
78 | if (!p) | |
79 | return -ENOMEM; | |
80 | allocated = true; | |
81 | } | |
82 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; | |
3bc8535a | 83 | hlist_for_each_entry(e, head, hlist) { |
d1f652f8 MD |
84 | if (id == e->id) |
85 | return -EEXIST; | |
86 | } | |
87 | e = kmalloc(sizeof(struct lttng_id_hash_node), GFP_KERNEL); | |
88 | if (!e) | |
89 | return -ENOMEM; | |
90 | e->id = id; | |
91 | hlist_add_head_rcu(&e->hlist, head); | |
92 | if (allocated) { | |
93 | rcu_assign_pointer(lf->p, p); | |
94 | } | |
95 | return 0; | |
96 | } | |
97 | ||
98 | static | |
99 | void id_tracker_del_node_rcu(struct lttng_id_hash_node *e) | |
100 | { | |
101 | hlist_del_rcu(&e->hlist); | |
102 | /* | |
103 | * We choose to use a heavyweight synchronize on removal here, | |
104 | * since removal of an ID from the tracker mask is a rare | |
105 | * operation, and we don't want to use more cache lines than | |
106 | * what we really need when doing the ID lookups, so we don't | |
107 | * want to afford adding a rcu_head field to those pid hash | |
108 | * node. | |
109 | */ | |
110 | synchronize_trace(); | |
111 | kfree(e); | |
112 | } | |
113 | ||
114 | /* | |
115 | * This removal is only used on destroy, so it does not need to support | |
116 | * concurrent RCU lookups. | |
117 | */ | |
118 | static | |
119 | void id_tracker_del_node(struct lttng_id_hash_node *e) | |
120 | { | |
121 | hlist_del(&e->hlist); | |
122 | kfree(e); | |
123 | } | |
124 | ||
125 | int lttng_id_tracker_del(struct lttng_id_tracker *lf, int id) | |
126 | { | |
127 | struct hlist_head *head; | |
128 | struct lttng_id_hash_node *e; | |
129 | struct lttng_id_tracker_rcu *p = lf->p; | |
130 | uint32_t hash = hash_32(id, 32); | |
131 | ||
132 | if (!p) | |
133 | return -ENOENT; | |
134 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; | |
135 | /* | |
136 | * No need of _safe iteration, because we stop traversal as soon | |
137 | * as we remove the entry. | |
138 | */ | |
3bc8535a | 139 | hlist_for_each_entry(e, head, hlist) { |
d1f652f8 MD |
140 | if (id == e->id) { |
141 | id_tracker_del_node_rcu(e); | |
142 | return 0; | |
143 | } | |
144 | } | |
145 | return -ENOENT; /* Not found */ | |
146 | } | |
147 | ||
148 | static void lttng_id_tracker_rcu_destroy(struct lttng_id_tracker_rcu *p) | |
149 | { | |
150 | int i; | |
151 | ||
152 | if (!p) | |
153 | return; | |
154 | for (i = 0; i < LTTNG_ID_TABLE_SIZE; i++) { | |
155 | struct hlist_head *head = &p->id_hash[i]; | |
156 | struct lttng_id_hash_node *e; | |
157 | struct hlist_node *tmp; | |
158 | ||
3bc8535a | 159 | hlist_for_each_entry_safe(e, tmp, head, hlist) |
d1f652f8 MD |
160 | id_tracker_del_node(e); |
161 | } | |
162 | kfree(p); | |
163 | } | |
164 | ||
165 | int lttng_id_tracker_empty_set(struct lttng_id_tracker *lf) | |
166 | { | |
167 | struct lttng_id_tracker_rcu *p, *oldp; | |
168 | ||
169 | p = lttng_id_tracker_rcu_create(); | |
170 | if (!p) | |
171 | return -ENOMEM; | |
172 | oldp = lf->p; | |
173 | rcu_assign_pointer(lf->p, p); | |
174 | synchronize_trace(); | |
175 | lttng_id_tracker_rcu_destroy(oldp); | |
176 | return 0; | |
177 | } | |
178 | ||
179 | void lttng_id_tracker_destroy(struct lttng_id_tracker *lf, bool rcu) | |
180 | { | |
181 | struct lttng_id_tracker_rcu *p = lf->p; | |
182 | ||
183 | if (!lf->p) | |
184 | return; | |
185 | rcu_assign_pointer(lf->p, NULL); | |
186 | if (rcu) | |
187 | synchronize_trace(); | |
188 | lttng_id_tracker_rcu_destroy(p); | |
189 | } |