MFV r266993:

4469 DTrace helper tracing should be dynamic

Reference:
https://illumos.org/issues/4469

Obtained from:	Illumos
Phabric:	D1551
Reviewed by:	markj
MFC after:	2 weeks

sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c

@@ -351,17 +351,22 @@ dtrace_id_t		dtrace_probeid_error;	/* special ERROR probe */
 
 /*
  * DTrace Helper Tracing Variables
+ *
+ * These variables should be set dynamically to enable helper tracing.  The
+ * only variables that should be set are dtrace_helptrace_enable (which should
+ * be set to a non-zero value to allocate helper tracing buffers on the next
+ * open of /dev/dtrace) and dtrace_helptrace_disable (which should be set to a
+ * non-zero value to deallocate helper tracing buffers on the next close of
+ * /dev/dtrace).  When (and only when) helper tracing is disabled, the
+ * buffer size may also be set via dtrace_helptrace_bufsize.
  */
-uint32_t dtrace_helptrace_next = 0;
-uint32_t dtrace_helptrace_nlocals;
-char	*dtrace_helptrace_buffer;
-int	dtrace_helptrace_bufsize = 512 * 1024;
-
-#ifdef DEBUG
-int	dtrace_helptrace_enabled = 1;
-#else
-int	dtrace_helptrace_enabled = 0;
-#endif
+int			dtrace_helptrace_enable = 0;
+int			dtrace_helptrace_disable = 0;
+int			dtrace_helptrace_bufsize = 16 * 1024 * 1024;
+uint32_t		dtrace_helptrace_nlocals;
+static dtrace_helptrace_t *dtrace_helptrace_buffer;
+static uint32_t		dtrace_helptrace_next = 0;
+static int		dtrace_helptrace_wrapped = 0;
 
 /*
  * DTrace Error Hashing
@@ -15199,10 +15204,10 @@ dtrace_helper_trace(dtrace_helper_action_t *helper,
     dtrace_mstate_t *mstate, dtrace_vstate_t *vstate, int where)
 {
 	uint32_t size, next, nnext, i;
-	dtrace_helptrace_t *ent;
+	dtrace_helptrace_t *ent, *buffer;
 	uint16_t flags = cpu_core[curcpu].cpuc_dtrace_flags;
 
-	if (!dtrace_helptrace_enabled)
+	if ((buffer = dtrace_helptrace_buffer) == NULL)
 		return;
 
 	ASSERT(vstate->dtvs_nlocals <= dtrace_helptrace_nlocals);
@@ -15230,10 +15235,12 @@ dtrace_helper_trace(dtrace_helper_action_t *helper,
 	/*
 	 * We have our slot; fill it in.
 	 */
-	if (nnext == size)
+	if (nnext == size) {
+		dtrace_helptrace_wrapped++;
 		next = 0;
+	}
 
-	ent = (dtrace_helptrace_t *)&dtrace_helptrace_buffer[next];
+	ent = (dtrace_helptrace_t *)((uintptr_t)buffer + next);
 	ent->dtht_helper = helper;
 	ent->dtht_where = where;
 	ent->dtht_nlocals = vstate->dtvs_nlocals;
@@ -15267,7 +15274,7 @@ dtrace_helper(int which, dtrace_mstate_t *mstate,
 	dtrace_helper_action_t *helper;
 	dtrace_vstate_t *vstate;
 	dtrace_difo_t *pred;
-	int i, trace = dtrace_helptrace_enabled;
+	int i, trace = dtrace_helptrace_buffer != NULL;
 
 	ASSERT(which >= 0 && which < DTRACE_NHELPER_ACTIONS);
 
@@ -16669,17 +16676,6 @@ dtrace_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
 	dtrace_anon_property();
 	mutex_exit(&cpu_lock);
 
-	/*
-	 * If DTrace helper tracing is enabled, we need to allocate the
-	 * trace buffer and initialize the values.
-	 */
-	if (dtrace_helptrace_enabled) {
-		ASSERT(dtrace_helptrace_buffer == NULL);
-		dtrace_helptrace_buffer =
-		    kmem_zalloc(dtrace_helptrace_bufsize, KM_SLEEP);
-		dtrace_helptrace_next = 0;
-	}
-
 	/*
 	 * If there are already providers, we must ask them to provide their
 	 * probes, and then match any anonymous enabling against them.  Note
@@ -16793,6 +16789,18 @@ dtrace_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
 		return (EBUSY);
 	}
 
+	if (dtrace_helptrace_enable && dtrace_helptrace_buffer == NULL) {
+		/*
+		 * If DTrace helper tracing is enabled, we need to allocate the
+		 * trace buffer and initialize the values.
+		 */
+		dtrace_helptrace_buffer =
+		    kmem_zalloc(dtrace_helptrace_bufsize, KM_SLEEP);
+		dtrace_helptrace_next = 0;
+		dtrace_helptrace_wrapped = 0;
+		dtrace_helptrace_enable = 0;
+	}
+
 	state = dtrace_state_create(devp, cred_p);
 #else
 	state = dtrace_state_create(dev);
@@ -16829,7 +16837,10 @@ dtrace_dtr(void *data)
 #ifdef illumos
 	minor_t minor = getminor(dev);
 	dtrace_state_t *state;
+#endif
+	dtrace_helptrace_t *buf = NULL;
 
+#ifdef illumos
 	if (minor == DTRACEMNRN_HELPER)
 		return (0);
 
@@ -16854,6 +16865,18 @@ dtrace_dtr(void *data)
 		dtrace_state_destroy(state->dts_anon);
 	}
 
+	if (dtrace_helptrace_disable) {
+		/*
+		 * If we have been told to disable helper tracing, set the
+		 * buffer to NULL before calling into dtrace_state_destroy();
+		 * we take advantage of its dtrace_sync() to know that no
+		 * CPU is in probe context with enabled helper tracing
+		 * after it returns.
+		 */
+		buf = dtrace_helptrace_buffer;
+		dtrace_helptrace_buffer = NULL;
+	}
+
 #ifdef illumos
 	dtrace_state_destroy(state);
 #else
@@ -16875,6 +16898,11 @@ dtrace_dtr(void *data)
 	--dtrace_opens;
 #endif
 
+	if (buf != NULL) {
+		kmem_free(buf, dtrace_helptrace_bufsize);
+		dtrace_helptrace_disable = 0;
+	}
+
 	mutex_exit(&dtrace_lock);
 	mutex_exit(&cpu_lock);
 
@@ -17772,11 +17800,6 @@ dtrace_detach(dev_info_t *dip, ddi_detach_cmd_t cmd)
 
 	mutex_exit(&cpu_lock);
 
-	if (dtrace_helptrace_enabled) {
-		kmem_free(dtrace_helptrace_buffer, dtrace_helptrace_bufsize);
-		dtrace_helptrace_buffer = NULL;
-	}
-
 	kmem_free(dtrace_probes, dtrace_nprobes * sizeof (dtrace_probe_t *));
 	dtrace_probes = NULL;
 	dtrace_nprobes = 0;

sys/cddl/dev/dtrace/dtrace_load.c

@@ -137,17 +137,6 @@ dtrace_load(void *dummy)
 
 	mutex_exit(&cpu_lock);
 
-	/*
-	 * If DTrace helper tracing is enabled, we need to allocate the
-	 * trace buffer and initialize the values.
-	 */
-	if (dtrace_helptrace_enabled) {
-		ASSERT(dtrace_helptrace_buffer == NULL);
-		dtrace_helptrace_buffer =
-		    kmem_zalloc(dtrace_helptrace_bufsize, KM_SLEEP);
-		dtrace_helptrace_next = 0;
-	}
-
 	mutex_exit(&dtrace_lock);
 	mutex_exit(&dtrace_provider_lock);
 

sys/cddl/dev/dtrace/dtrace_unload.c

@@ -69,11 +69,6 @@ dtrace_unload()
 
 	mutex_exit(&cpu_lock);
 
-	if (dtrace_helptrace_enabled) {
-		kmem_free(dtrace_helptrace_buffer, 0);
-		dtrace_helptrace_buffer = NULL;
-	}
-
 	if (dtrace_probes != NULL) {
 		kmem_free(dtrace_probes, 0);
 		dtrace_probes = NULL;