ltt-events.c

   1 /*
   2  * ltt-events.c
   3  *
   4  * Copyright 2010 (c) - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * Holds LTTng per-session event registry.
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/list.h>
  11 #include <linux/mutex.h>
  12 #include <linux/sched.h>
  13 #include <linux/slab.h>
  14 #include "wrapper/vmalloc.h"    /* for wrapper_vmalloc_sync_all() */
  15 #include "ltt-events.h"
  16
  17 static LIST_HEAD(sessions);
  18 static LIST_HEAD(ltt_transport_list);
  19 static DEFINE_MUTEX(sessions_mutex);
  20 static struct kmem_cache *event_cache;
  21
  22 static void synchronize_trace(void)
  23 {
  24         synchronize_sched();
  25 #ifdef CONFIG_PREEMPT_RT
  26         synchronize_rcu();
  27 #endif
  28 }
  29
  30 struct ltt_session *ltt_session_create(void)
  31 {
  32         struct ltt_session *session;
  33
  34         mutex_lock(&sessions_mutex);
  35         session = kzalloc(sizeof(struct ltt_session), GFP_KERNEL);
  36         if (!session)
  37                 return NULL;
  38         INIT_LIST_HEAD(&session->chan);
  39         INIT_LIST_HEAD(&session->events);
  40         list_add(&session->list, &sessions);
  41         mutex_unlock(&sessions_mutex);
  42         return session;
  43 }
  44
  45 void ltt_session_destroy(struct ltt_session *session)
  46 {
  47         struct ltt_channel *chan, *tmpchan;
  48         struct ltt_event *event, *tmpevent;
  49         int ret;
  50
  51         mutex_lock(&sessions_mutex);
  52         ACCESS_ONCE(session->active) = 0;
  53         list_for_each_entry(event, &session->events, list) {
  54                 ret = _ltt_event_unregister(event);
  55                 WARN_ON(ret);
  56         }
  57         synchronize_trace();    /* Wait for in-flight events to complete */
  58         list_for_each_entry_safe(event, tmpevent, &session->events, list)
  59                 _ltt_event_destroy(event);
  60         list_for_each_entry_safe(chan, tmpchan, &session->chan, list)
  61                 _ltt_channel_destroy(chan);
  62         list_del(&session->list);
  63         mutex_unlock(&sessions_mutex);
  64         kfree(session);
  65 }
  66
  67 int ltt_session_start(struct ltt_session *session)
  68 {
  69         int ret = 0;
  70
  71         mutex_lock(&sessions_mutex);
  72         if (session->active) {
  73                 ret = -EBUSY;
  74                 goto end;
  75         }
  76         ACCESS_ONCE(session->active) = 1;
  77         synchronize_trace();    /* Wait for in-flight events to complete */
  78 end:
  79         mutex_unlock(&sessions_mutex);
  80         return ret;
  81 }
  82
  83 int ltt_session_stop(struct ltt_session *session)
  84 {
  85         int ret = 0;
  86
  87         mutex_lock(&sessions_mutex);
  88         if (!session->active) {
  89                 ret = -EBUSY;
  90                 goto end;
  91         }
  92         ACCESS_ONCE(session->active) = 0;
  93         synchronize_trace();    /* Wait for in-flight events to complete */
  94 end:
  95         mutex_unlock(&sessions_mutex);
  96         return ret;
  97 }
  98
  99 static struct ltt_transport *ltt_transport_find(const char *name)
 100 {
 101         struct ltt_transport *transport;
 102
 103         list_for_each_entry(transport, &ltt_transport_list, node) {
 104                 if (!strcmp(transport->name, name))
 105                         return transport;
 106         }
 107         return NULL;
 108 }
 109
 110 struct ltt_channel *ltt_channel_create(struct ltt_session *session,
 111                                        const char *transport_name,
 112                                        void *buf_addr,
 113                                        size_t subbuf_size, size_t num_subbuf,
 114                                        unsigned int switch_timer_interval,
 115                                        unsigned int read_timer_interval)
 116 {
 117         struct ltt_channel *chan;
 118         struct ltt_transport *transport;
 119
 120         mutex_lock(&sessions_mutex);
 121         if (session->active) {
 122                 printk(KERN_WARNING "LTTng refusing to add channel to active session\n");
 123                 goto active;    /* Refuse to add channel to active session */
 124         }
 125         transport = ltt_transport_find(transport_name);
 126         if (!transport) {
 127                 printk(KERN_WARNING "LTTng transport %s not found\n",
 128                        transport_name);
 129                 goto notransport;
 130         }
 131         chan = kzalloc(sizeof(struct ltt_channel), GFP_KERNEL);
 132         if (!chan)
 133                 goto nomem;
 134         chan->session = session;
 135         init_waitqueue_head(&chan->notify_wait);
 136         chan->chan = transport->ops.channel_create("[lttng]", session, buf_addr,
 137                         subbuf_size, num_subbuf, switch_timer_interval,
 138                         read_timer_interval);
 139         if (!chan->chan)
 140                 goto create_error;
 141         chan->ops = &transport->ops;
 142         list_add(&chan->list, &session->chan);
 143         mutex_unlock(&sessions_mutex);
 144         return chan;
 145
 146 create_error:
 147         kfree(chan);
 148 nomem:
 149 notransport:
 150 active:
 151         mutex_unlock(&sessions_mutex);
 152         return NULL;
 153 }
 154
 155 /*
 156  * Only used internally at session destruction.
 157  */
 158 void _ltt_channel_destroy(struct ltt_channel *chan)
 159 {
 160         chan->ops->channel_destroy(chan->chan);
 161         list_del(&chan->list);
 162         kfree(chan);
 163 }
 164
 165 /*
 166  * Supports event creation while tracing session is active.
 167  */
 168 struct ltt_event *ltt_event_create(struct ltt_channel *chan, char *name,
 169                                    enum instrum_type itype,
 170                                    const struct lttng_event_desc *event_desc,
 171                                    void *filter)
 172 {
 173         struct ltt_event *event;
 174         int ret;
 175
 176         mutex_lock(&sessions_mutex);
 177         if (chan->free_event_id == -1UL)
 178                 goto full;
 179         /*
 180          * This is O(n^2) (for each event, the loop is called at event
 181          * creation). Might require a hash if we have lots of events.
 182          */
 183         list_for_each_entry(event, &chan->session->events, list)
 184                 if (!strcmp(event->desc->name, name))
 185                         goto exist;
 186         event = kmem_cache_zalloc(event_cache, GFP_KERNEL);
 187         if (!event)
 188                 goto cache_error;
 189         event->chan = chan;
 190         event->desc = event_desc;
 191         event->filter = filter;
 192         event->id = chan->free_event_id++;
 193         event->itype = itype;
 194         /* Populate ltt_event structure before tracepoint registration. */
 195         smp_wmb();
 196         switch (itype) {
 197         case INSTRUM_TRACEPOINTS:
 198                 ret = tracepoint_probe_register(name, event_desc->probe_callback,
 199                                                 event);
 200                 if (ret)
 201                         goto register_error;
 202                 break;
 203         default:
 204                 WARN_ON_ONCE(1);
 205         }
 206         list_add(&event->list, &chan->session->events);
 207         mutex_unlock(&sessions_mutex);
 208         return event;
 209
 210 register_error:
 211         kmem_cache_free(event_cache, event);
 212 cache_error:
 213 exist:
 214 full:
 215         mutex_unlock(&sessions_mutex);
 216         return NULL;
 217 }
 218
 219 /*
 220  * Only used internally at session destruction.
 221  */
 222 int _ltt_event_unregister(struct ltt_event *event)
 223 {
 224         int ret = -EINVAL;
 225
 226         switch (event->itype) {
 227         case INSTRUM_TRACEPOINTS:
 228                 ret = tracepoint_probe_unregister(event->desc->name,
 229                                                   event->desc->probe_callback,
 230                                                   event);
 231                 if (ret)
 232                         return ret;
 233                 break;
 234         default:
 235                 WARN_ON_ONCE(1);
 236         }
 237         return ret;
 238 }
 239
 240 /*
 241  * Only used internally at session destruction.
 242  */
 243 void _ltt_event_destroy(struct ltt_event *event)
 244 {
 245         ltt_event_put(event->desc);
 246         list_del(&event->list);
 247         kmem_cache_free(event_cache, event);
 248 }
 249
 250 /**
 251  * ltt_transport_register - LTT transport registration
 252  * @transport: transport structure
 253  *
 254  * Registers a transport which can be used as output to extract the data out of
 255  * LTTng. The module calling this registration function must ensure that no
 256  * trap-inducing code will be executed by the transport functions. E.g.
 257  * vmalloc_sync_all() must be called between a vmalloc and the moment the memory
 258  * is made visible to the transport function. This registration acts as a
 259  * vmalloc_sync_all. Therefore, only if the module allocates virtual memory
 260  * after its registration must it synchronize the TLBs.
 261  */
 262 void ltt_transport_register(struct ltt_transport *transport)
 263 {
 264         /*
 265          * Make sure no page fault can be triggered by the module about to be
 266          * registered. We deal with this here so we don't have to call
 267          * vmalloc_sync_all() in each module's init.
 268          */
 269         wrapper_vmalloc_sync_all();
 270
 271         mutex_lock(&sessions_mutex);
 272         list_add_tail(&transport->node, &ltt_transport_list);
 273         mutex_unlock(&sessions_mutex);
 274 }
 275 EXPORT_SYMBOL_GPL(ltt_transport_register);
 276
 277 /**
 278  * ltt_transport_unregister - LTT transport unregistration
 279  * @transport: transport structure
 280  */
 281 void ltt_transport_unregister(struct ltt_transport *transport)
 282 {
 283         mutex_lock(&sessions_mutex);
 284         list_del(&transport->node);
 285         mutex_unlock(&sessions_mutex);
 286 }
 287 EXPORT_SYMBOL_GPL(ltt_transport_unregister);
 288
 289
 290 static int __init ltt_events_init(void)
 291 {
 292         int ret;
 293
 294         event_cache = KMEM_CACHE(ltt_event, 0);
 295         if (!event_cache)
 296                 return -ENOMEM;
 297         ret = ltt_debugfs_abi_init();
 298         if (ret)
 299                 goto error_abi;
 300         return 0;
 301 error_abi:
 302         kmem_cache_destroy(event_cache);
 303         return ret;
 304 }
 305
 306 module_init(ltt_events_init);
 307
 308 static void __exit ltt_events_exit(void)
 309 {
 310         struct ltt_session *session, *tmpsession;
 311
 312         ltt_debugfs_abi_exit();
 313         list_for_each_entry_safe(session, tmpsession, &sessions, list)
 314                 ltt_session_destroy(session);
 315         kmem_cache_destroy(event_cache);
 316 }
 317
 318 module_exit(ltt_events_exit);
 319
 320 MODULE_LICENSE("GPL and additional rights");
 321 MODULE_AUTHOR("Mathieu Desnoyers <mathieu.desnoyers@efficios.com>");
 322 MODULE_DESCRIPTION("LTTng Events");