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/rculist.h>
  29 #include <linux/hash.h>
  30 #include <linux/rcupdate.h>
  31
  32 #include "wrapper/tracepoint.h"
  33 #include "lttng-events.h"
  34
  35 /*
  36  * Hash table is allocated and freed when there are no possible
  37  * concurrent lookups (ensured by the alloc/free caller). However,
  38  * there can be concurrent RCU lookups vs add/del operations.
  39  *
  40  * Concurrent updates of the PID hash table are forbidden: the caller
  41  * must ensure mutual exclusion. This is currently done by holding the
  42  * sessions_mutex across calls to create, destroy, add, and del
  43  * functions of this API.
  44  */
  45 struct lttng_pid_hash_node {
  46         struct hlist_node hlist;
  47         int pid;
  48 };
  49
  50 /*
  51  * Lookup performed from RCU read-side critical section (RCU sched),
  52  * protected by preemption off at the tracepoint call site.
  53  * Return 1 if found, 0 if not found.
  54  */
  55 bool lttng_pid_tracker_lookup(struct lttng_pid_tracker *lpf, int pid)
  56 {
  57         struct hlist_head *head;
  58         struct lttng_pid_hash_node *e;
  59         uint32_t hash = hash_32(pid, 32);
  60
  61         head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
  62         hlist_for_each_entry_rcu_notrace(e, head, hlist) {
  63                 if (pid == e->pid)
  64                         return 1;       /* Found */
  65         }
  66         return 0;
  67 }
  68 EXPORT_SYMBOL_GPL(lttng_pid_tracker_lookup);
  69
  70 /*
  71  * Tracker add and del operations support concurrent RCU lookups.
  72  */
  73 int lttng_pid_tracker_add(struct lttng_pid_tracker *lpf, int pid)
  74 {
  75         struct hlist_head *head;
  76         struct lttng_pid_hash_node *e;
  77         uint32_t hash = hash_32(pid, 32);
  78
  79         head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
  80         hlist_for_each_entry(e, head, hlist) {
  81                 if (pid == e->pid)
  82                         return -EEXIST;
  83         }
  84         e = kmalloc(sizeof(struct lttng_pid_hash_node), GFP_KERNEL);
  85         if (!e)
  86                 return -ENOMEM;
  87         e->pid = pid;
  88         hlist_add_head_rcu(&e->hlist, head);
  89         return 0;
  90 }
  91
  92 static
  93 void pid_tracker_del_node_rcu(struct lttng_pid_hash_node *e)
  94 {
  95         hlist_del_rcu(&e->hlist);
  96         /*
  97          * We choose to use a heavyweight synchronize on removal here,
  98          * since removal of a PID from the tracker mask is a rare
  99          * operation, and we don't want to use more cache lines than
 100          * what we really need when doing the PID lookups, so we don't
 101          * want to afford adding a rcu_head field to those pid hash
 102          * node.
 103          */
 104         synchronize_trace();
 105         kfree(e);
 106 }
 107
 108 /*
 109  * This removal is only used on destroy, so it does not need to support
 110  * concurrent RCU lookups.
 111  */
 112 static
 113 void pid_tracker_del_node(struct lttng_pid_hash_node *e)
 114 {
 115         hlist_del(&e->hlist);
 116         kfree(e);
 117 }
 118
 119 int lttng_pid_tracker_del(struct lttng_pid_tracker *lpf, int pid)
 120 {
 121         struct hlist_head *head;
 122         struct lttng_pid_hash_node *e;
 123         uint32_t hash = hash_32(pid, 32);
 124
 125         head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)];
 126         /*
 127          * No need of _safe iteration, because we stop traversal as soon
 128          * as we remove the entry.
 129          */
 130         hlist_for_each_entry(e, head, hlist) {
 131                 if (pid == e->pid) {
 132                         pid_tracker_del_node_rcu(e);
 133                         return 0;
 134                 }
 135         }
 136         return -ENOENT; /* Not found */
 137 }
 138
 139 struct lttng_pid_tracker *lttng_pid_tracker_create(void)
 140 {
 141         return kzalloc(sizeof(struct lttng_pid_tracker), GFP_KERNEL);
 142 }
 143
 144 void lttng_pid_tracker_destroy(struct lttng_pid_tracker *lpf)
 145 {
 146         int i;
 147
 148         for (i = 0; i < LTTNG_PID_TABLE_SIZE; i++) {
 149                 struct hlist_head *head = &lpf->pid_hash[i];
 150                 struct lttng_pid_hash_node *e;
 151                 struct hlist_node *tmp;
 152
 153                 hlist_for_each_entry_safe(e, tmp, head, hlist)
 154                         pid_tracker_del_node(e);
 155         }
 156         kfree(lpf);
 157 }