lttng-tracker-pid.c

   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_pid_tracker_get_node_pid(const struct lttng_pid_hash_node *node)
  47 {
  48         return node->pid;
  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 1 if found, 0 if not found.
  55  */
  56 bool lttng_pid_tracker_lookup(struct lttng_pid_tracker *lpf, int pid)
  57 {
  58         struct hlist_head *head;
  59         struct lttng_pid_hash_node *e;
  60         uint32_t hash = hash_32(pid, 32);
  61
  62         head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
  63         lttng_hlist_for_each_entry_rcu(e, head, hlist) {
  64                 if (pid == e->pid)
  65                         return 1;       /* Found */
  66         }
  67         return 0;
  68 }
  69 EXPORT_SYMBOL_GPL(lttng_pid_tracker_lookup);
  70
  71 /*
  72  * Tracker add and del operations support concurrent RCU lookups.
  73  */
  74 int lttng_pid_tracker_add(struct lttng_pid_tracker *lpf, int pid)
  75 {
  76         struct hlist_head *head;
  77         struct lttng_pid_hash_node *e;
  78         uint32_t hash = hash_32(pid, 32);
  79
  80         head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
  81         lttng_hlist_for_each_entry(e, head, hlist) {
  82                 if (pid == e->pid)
  83                         return -EEXIST;
  84         }
  85         e = kmalloc(sizeof(struct lttng_pid_hash_node), GFP_KERNEL);
  86         if (!e)
  87                 return -ENOMEM;
  88         e->pid = pid;
  89         hlist_add_head_rcu(&e->hlist, head);
  90         return 0;
  91 }
  92
  93 static
  94 void pid_tracker_del_node_rcu(struct lttng_pid_hash_node *e)
  95 {
  96         hlist_del_rcu(&e->hlist);
  97         /*
  98          * We choose to use a heavyweight synchronize on removal here,
  99          * since removal of a PID from the tracker mask is a rare
 100          * operation, and we don't want to use more cache lines than
 101          * what we really need when doing the PID lookups, so we don't
 102          * want to afford adding a rcu_head field to those pid hash
 103          * node.
 104          */
 105         synchronize_trace();
 106         kfree(e);
 107 }
 108
 109 /*
 110  * This removal is only used on destroy, so it does not need to support
 111  * concurrent RCU lookups.
 112  */
 113 static
 114 void pid_tracker_del_node(struct lttng_pid_hash_node *e)
 115 {
 116         hlist_del(&e->hlist);
 117         kfree(e);
 118 }
 119
 120 int lttng_pid_tracker_del(struct lttng_pid_tracker *lpf, int pid)
 121 {
 122         struct hlist_head *head;
 123         struct lttng_pid_hash_node *e;
 124         uint32_t hash = hash_32(pid, 32);
 125
 126         head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
 127         /*
 128          * No need of _safe iteration, because we stop traversal as soon
 129          * as we remove the entry.
 130          */
 131         lttng_hlist_for_each_entry(e, head, hlist) {
 132                 if (pid == e->pid) {
 133                         pid_tracker_del_node_rcu(e);
 134                         return 0;
 135                 }
 136         }
 137         return -ENOENT; /* Not found */
 138 }
 139
 140 struct lttng_pid_tracker *lttng_pid_tracker_create(void)
 141 {
 142         return kzalloc(sizeof(struct lttng_pid_tracker), GFP_KERNEL);
 143 }
 144
 145 void lttng_pid_tracker_destroy(struct lttng_pid_tracker *lpf)
 146 {
 147         int i;
 148
 149         for (i = 0; i < LTTNG_PID_TABLE_SIZE; i++) {
 150                 struct hlist_head *head = &lpf->pid_hash[i];
 151                 struct lttng_pid_hash_node *e;
 152                 struct hlist_node *tmp;
 153
 154                 lttng_hlist_for_each_entry_safe(e, tmp, head, hlist)
 155                         pid_tracker_del_node(e);
 156         }
 157         kfree(lpf);
 158 }