| 1 | /* |
| 2 | * lttng-tracker-pid.c |
| 3 | * |
| 4 | * LTTng Process ID trackering. |
| 5 | * |
| 6 | * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 7 | * |
| 8 | * This library is free software; you can redistribute it and/or |
| 9 | * modify it under the terms of the GNU Lesser General Public |
| 10 | * License as published by the Free Software Foundation; only |
| 11 | * version 2.1 of the License. |
| 12 | * |
| 13 | * This library is distributed in the hope that it will be useful, |
| 14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 16 | * Lesser General Public License for more details. |
| 17 | * |
| 18 | * You should have received a copy of the GNU Lesser General Public |
| 19 | * License along with this library; if not, write to the Free Software |
| 20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 21 | */ |
| 22 | |
| 23 | #include <linux/module.h> |
| 24 | #include <linux/slab.h> |
| 25 | #include <linux/err.h> |
| 26 | #include <linux/seq_file.h> |
| 27 | #include <linux/stringify.h> |
| 28 | #include <linux/hash.h> |
| 29 | #include <linux/rcupdate.h> |
| 30 | |
| 31 | #include <wrapper/tracepoint.h> |
| 32 | #include <wrapper/rcu.h> |
| 33 | #include <wrapper/list.h> |
| 34 | #include <lttng-events.h> |
| 35 | |
| 36 | /* |
| 37 | * Hash table is allocated and freed when there are no possible |
| 38 | * concurrent lookups (ensured by the alloc/free caller). However, |
| 39 | * there can be concurrent RCU lookups vs add/del operations. |
| 40 | * |
| 41 | * Concurrent updates of the PID hash table are forbidden: the caller |
| 42 | * must ensure mutual exclusion. This is currently done by holding the |
| 43 | * sessions_mutex across calls to create, destroy, add, and del |
| 44 | * functions of this API. |
| 45 | */ |
| 46 | int lttng_id_tracker_get_node_id(const struct lttng_id_hash_node *node) |
| 47 | { |
| 48 | return node->id; |
| 49 | } |
| 50 | |
| 51 | /* |
| 52 | * Lookup performed from RCU read-side critical section (RCU sched), |
| 53 | * protected by preemption off at the tracepoint call site. |
| 54 | * Return true if found, false if not found. |
| 55 | */ |
| 56 | bool lttng_id_tracker_lookup(struct lttng_id_tracker_rcu *p, int id) |
| 57 | { |
| 58 | struct hlist_head *head; |
| 59 | struct lttng_id_hash_node *e; |
| 60 | uint32_t hash = hash_32(id, 32); |
| 61 | |
| 62 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; |
| 63 | lttng_hlist_for_each_entry_rcu(e, head, hlist) { |
| 64 | if (id == e->id) |
| 65 | return true; /* Found */ |
| 66 | } |
| 67 | return false; |
| 68 | } |
| 69 | EXPORT_SYMBOL_GPL(lttng_id_tracker_lookup); |
| 70 | |
| 71 | static struct lttng_id_tracker_rcu *lttng_id_tracker_rcu_create(void) |
| 72 | { |
| 73 | struct lttng_id_tracker_rcu *tracker; |
| 74 | |
| 75 | tracker = kzalloc(sizeof(struct lttng_id_tracker_rcu), GFP_KERNEL); |
| 76 | if (!tracker) |
| 77 | return NULL; |
| 78 | return tracker; |
| 79 | } |
| 80 | |
| 81 | /* |
| 82 | * Tracker add and del operations support concurrent RCU lookups. |
| 83 | */ |
| 84 | int lttng_id_tracker_add(struct lttng_id_tracker *lf, int id) |
| 85 | { |
| 86 | struct hlist_head *head; |
| 87 | struct lttng_id_hash_node *e; |
| 88 | struct lttng_id_tracker_rcu *p = lf->p; |
| 89 | uint32_t hash = hash_32(id, 32); |
| 90 | bool allocated = false; |
| 91 | |
| 92 | if (!p) { |
| 93 | p = lttng_id_tracker_rcu_create(); |
| 94 | if (!p) |
| 95 | return -ENOMEM; |
| 96 | allocated = true; |
| 97 | } |
| 98 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; |
| 99 | lttng_hlist_for_each_entry(e, head, hlist) { |
| 100 | if (id == e->id) |
| 101 | return -EEXIST; |
| 102 | } |
| 103 | e = kmalloc(sizeof(struct lttng_id_hash_node), GFP_KERNEL); |
| 104 | if (!e) |
| 105 | return -ENOMEM; |
| 106 | e->id = id; |
| 107 | hlist_add_head_rcu(&e->hlist, head); |
| 108 | if (allocated) { |
| 109 | rcu_assign_pointer(lf->p, p); |
| 110 | } |
| 111 | return 0; |
| 112 | } |
| 113 | |
| 114 | static |
| 115 | void id_tracker_del_node_rcu(struct lttng_id_hash_node *e) |
| 116 | { |
| 117 | hlist_del_rcu(&e->hlist); |
| 118 | /* |
| 119 | * We choose to use a heavyweight synchronize on removal here, |
| 120 | * since removal of an ID from the tracker mask is a rare |
| 121 | * operation, and we don't want to use more cache lines than |
| 122 | * what we really need when doing the ID lookups, so we don't |
| 123 | * want to afford adding a rcu_head field to those pid hash |
| 124 | * node. |
| 125 | */ |
| 126 | synchronize_trace(); |
| 127 | kfree(e); |
| 128 | } |
| 129 | |
| 130 | /* |
| 131 | * This removal is only used on destroy, so it does not need to support |
| 132 | * concurrent RCU lookups. |
| 133 | */ |
| 134 | static |
| 135 | void id_tracker_del_node(struct lttng_id_hash_node *e) |
| 136 | { |
| 137 | hlist_del(&e->hlist); |
| 138 | kfree(e); |
| 139 | } |
| 140 | |
| 141 | int lttng_id_tracker_del(struct lttng_id_tracker *lf, int id) |
| 142 | { |
| 143 | struct hlist_head *head; |
| 144 | struct lttng_id_hash_node *e; |
| 145 | struct lttng_id_tracker_rcu *p = lf->p; |
| 146 | uint32_t hash = hash_32(id, 32); |
| 147 | |
| 148 | if (!p) |
| 149 | return -ENOENT; |
| 150 | head = &p->id_hash[hash & (LTTNG_ID_TABLE_SIZE - 1)]; |
| 151 | /* |
| 152 | * No need of _safe iteration, because we stop traversal as soon |
| 153 | * as we remove the entry. |
| 154 | */ |
| 155 | lttng_hlist_for_each_entry(e, head, hlist) { |
| 156 | if (id == e->id) { |
| 157 | id_tracker_del_node_rcu(e); |
| 158 | return 0; |
| 159 | } |
| 160 | } |
| 161 | return -ENOENT; /* Not found */ |
| 162 | } |
| 163 | |
| 164 | static void lttng_id_tracker_rcu_destroy(struct lttng_id_tracker_rcu *p) |
| 165 | { |
| 166 | int i; |
| 167 | |
| 168 | if (!p) |
| 169 | return; |
| 170 | for (i = 0; i < LTTNG_ID_TABLE_SIZE; i++) { |
| 171 | struct hlist_head *head = &p->id_hash[i]; |
| 172 | struct lttng_id_hash_node *e; |
| 173 | struct hlist_node *tmp; |
| 174 | |
| 175 | lttng_hlist_for_each_entry_safe(e, tmp, head, hlist) |
| 176 | id_tracker_del_node(e); |
| 177 | } |
| 178 | kfree(p); |
| 179 | } |
| 180 | |
| 181 | int lttng_id_tracker_empty_set(struct lttng_id_tracker *lf) |
| 182 | { |
| 183 | struct lttng_id_tracker_rcu *p, *oldp; |
| 184 | |
| 185 | p = lttng_id_tracker_rcu_create(); |
| 186 | if (!p) |
| 187 | return -ENOMEM; |
| 188 | oldp = lf->p; |
| 189 | rcu_assign_pointer(lf->p, p); |
| 190 | synchronize_trace(); |
| 191 | lttng_id_tracker_rcu_destroy(oldp); |
| 192 | return 0; |
| 193 | } |
| 194 | |
| 195 | void lttng_id_tracker_destroy(struct lttng_id_tracker *lf, bool rcu) |
| 196 | { |
| 197 | struct lttng_id_tracker_rcu *p = lf->p; |
| 198 | |
| 199 | if (!lf->p) |
| 200 | return; |
| 201 | rcu_assign_pointer(lf->p, NULL); |
| 202 | if (rcu) |
| 203 | synchronize_trace(); |
| 204 | lttng_id_tracker_rcu_destroy(p); |
| 205 | } |