1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
5 * LTTng Process ID tracking.
7 * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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>
18 #include <wrapper/tracepoint.h>
19 #include <wrapper/rcu.h>
20 #include <wrapper/list.h>
21 #include <lttng-events.h>
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.
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.
33 int lttng_id_tracker_get_node_id(const struct lttng_id_hash_node
*node
)
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.
43 bool lttng_id_tracker_lookup(struct lttng_id_tracker_rcu
*p
, int id
)
45 struct hlist_head
*head
;
46 struct lttng_id_hash_node
*e
;
47 uint32_t hash
= hash_32(id
, 32);
49 head
= &p
->id_hash
[hash
& (LTTNG_ID_TABLE_SIZE
- 1)];
50 lttng_hlist_for_each_entry_rcu(e
, head
, hlist
) {
52 return true; /* Found */
56 EXPORT_SYMBOL_GPL(lttng_id_tracker_lookup
);
58 static struct lttng_id_tracker_rcu
*lttng_id_tracker_rcu_create(void)
60 struct lttng_id_tracker_rcu
*tracker
;
62 tracker
= kzalloc(sizeof(struct lttng_id_tracker_rcu
), GFP_KERNEL
);
69 * Tracker add and del operations support concurrent RCU lookups.
71 int lttng_id_tracker_add(struct lttng_id_tracker
*lf
, int id
)
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;
81 p
= lttng_id_tracker_rcu_create();
86 head
= &p
->id_hash
[hash
& (LTTNG_ID_TABLE_SIZE
- 1)];
87 lttng_hlist_for_each_entry(e
, head
, hlist
) {
93 e
= kmalloc(sizeof(struct lttng_id_hash_node
), GFP_KERNEL
);
99 hlist_add_head_rcu(&e
->hlist
, head
);
101 rcu_assign_pointer(lf
->p
, p
);
113 void id_tracker_del_node_rcu(struct lttng_id_hash_node
*e
)
115 hlist_del_rcu(&e
->hlist
);
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
129 * This removal is only used on destroy, so it does not need to support
130 * concurrent RCU lookups.
133 void id_tracker_del_node(struct lttng_id_hash_node
*e
)
135 hlist_del(&e
->hlist
);
139 int lttng_id_tracker_del(struct lttng_id_tracker
*lf
, int id
)
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);
148 head
= &p
->id_hash
[hash
& (LTTNG_ID_TABLE_SIZE
- 1)];
150 * No need of _safe iteration, because we stop traversal as soon
151 * as we remove the entry.
153 lttng_hlist_for_each_entry(e
, head
, hlist
) {
155 id_tracker_del_node_rcu(e
);
159 return -ENOENT
; /* Not found */
162 static void lttng_id_tracker_rcu_destroy(struct lttng_id_tracker_rcu
*p
)
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
;
173 lttng_hlist_for_each_entry_safe(e
, tmp
, head
, hlist
)
174 id_tracker_del_node(e
);
179 int lttng_id_tracker_empty_set(struct lttng_id_tracker
*lf
)
181 struct lttng_id_tracker_rcu
*p
, *oldp
;
183 p
= lttng_id_tracker_rcu_create();
187 rcu_assign_pointer(lf
->p
, p
);
189 lttng_id_tracker_rcu_destroy(oldp
);
193 void lttng_id_tracker_destroy(struct lttng_id_tracker
*lf
, bool rcu
)
195 struct lttng_id_tracker_rcu
*p
= lf
->p
;
199 rcu_assign_pointer(lf
->p
, NULL
);
202 lttng_id_tracker_rcu_destroy(p
);
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