[PATCH v2 7/7] tracing: tprobe-events: Register tracepoint when enable tprobe event

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

As same as fprobe, register tracepoint stub function only when enabling
tprobe events. The major changes are introducing a list of
tracepoint_user and its lock, and tprobe_event_module_nb, which is
another module notifier for module loading/unloading.  By spliting the
lock from event_mutex and a module notifier for trace_fprobe, it
solved AB-BA lock dependency issue between event_mutex and
tracepoint_module_list_mutex.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v2:
  - Add some input error checkings.
---
 kernel/trace/trace_fprobe.c |  382 ++++++++++++++++++++++++-------------------
 1 file changed, 217 insertions(+), 165 deletions(-)

diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index cee5153da7ec..fb94f935c5d3 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -7,7 +7,9 @@
 #include <asm/ptrace.h>
 
 #include <linux/fprobe.h>
+#include <linux/list.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/rculist.h>
 #include <linux/security.h>
 #include <linux/tracepoint.h>
@@ -37,15 +39,21 @@ static struct dyn_event_operations trace_fprobe_ops = {
 	.match = trace_fprobe_match,
 };
 
+/* List of tracepoint_user */
+static LIST_HEAD(tracepoint_user_list);
+static DEFINE_MUTEX(tracepoint_user_mutex);
+
+/* While living tracepoint_user, @tpoint can be NULL and @refcount != 0. */
 struct tracepoint_user {
+	struct list_head	list;
+	const char		*name;
 	struct tracepoint	*tpoint;
 	unsigned int		refcount;
 };
 
-static bool tracepoint_user_is_registered(struct tracepoint_user *tuser)
-{
-	return tuser && tuser->tpoint;
-}
+/* NOTE: you must lock tracepoint_user_mutex. */
+#define for_each_tracepoint_user(tuser)		\
+	list_for_each_entry(tuser, &tracepoint_user_list, list)
 
 static int tracepoint_user_register(struct tracepoint_user *tuser)
 {
@@ -75,58 +83,111 @@ static unsigned long tracepoint_user_ip(struct tracepoint_user *tuser)
 	return (unsigned long)tuser->tpoint->probestub;
 }
 
-static bool tracepoint_user_within_module(struct tracepoint_user *tuser,
-					  struct module *mod)
+static void __tracepoint_user_free(struct tracepoint_user *tuser)
 {
-	return within_module(tracepoint_user_ip(tuser), mod);
+	if (!tuser)
+		return;
+	kfree(tuser->name);
+	kfree(tuser);
 }
 
-static struct tracepoint_user *tracepoint_user_allocate(struct tracepoint *tpoint)
+DEFINE_FREE(tuser_free, struct tracepoint_user *, __tracepoint_user_free(_T))
+
+static struct tracepoint_user *__tracepoint_user_init(const char *name, struct tracepoint *tpoint)
 {
-	struct tracepoint_user *tuser;
+	struct tracepoint_user *tuser __free(tuser_free) = NULL;
+	int ret;
 
 	tuser = kzalloc(sizeof(*tuser), GFP_KERNEL);
 	if (!tuser)
 		return NULL;
+	tuser->name = kstrdup(name, GFP_KERNEL);
+	if (!tuser->name)
+		return NULL;
+
+	if (tpoint) {
+		ret = tracepoint_user_register(tuser);
+		if (ret)
+			return ERR_PTR(ret);
+	}
+
 	tuser->tpoint = tpoint;
 	tuser->refcount = 1;
+	INIT_LIST_HEAD(&tuser->list);
+	list_add(&tuser->list, &tracepoint_user_list);
 
-	return tuser;
+	return_ptr(tuser);
 }
 
-/* These must be called with event_mutex */
-static void tracepoint_user_get(struct tracepoint_user *tuser)
-{
-	tuser->refcount++;
-}
+static struct tracepoint *find_tracepoint(const char *tp_name,
+	struct module **tp_mod);
 
-static void tracepoint_user_put(struct tracepoint_user *tuser)
+/*
+ * Get tracepoint_user if exist, or allocate new one and register it.
+ * If tracepoint is on a module, get its refcounter too.
+ * This returns errno or NULL (not loaded yet) or tracepoint_user.
+ */
+static struct tracepoint_user *tracepoint_user_find_get(const char *name, struct module **pmod)
 {
-	if (--tuser->refcount > 0)
-		return;
+	struct module *mod __free(module_put) = NULL;
+	struct tracepoint_user *tuser;
+	struct tracepoint *tpoint;
 
-	if (tracepoint_user_is_registered(tuser))
-		tracepoint_user_unregister(tuser);
-	kfree(tuser);
+	if (!name || !pmod)
+		return ERR_PTR(-EINVAL);
+
+	/* Get and lock the module which has tracepoint. */
+	tpoint = find_tracepoint(name, &mod);
+
+	guard(mutex)(&tracepoint_user_mutex);
+	/* Search existing tracepoint_user */
+	for_each_tracepoint_user(tuser) {
+		if (!strcmp(tuser->name, name)) {
+			tuser->refcount++;
+			*pmod = no_free_ptr(mod);
+			return tuser;
+		}
+	}
+
+	/* The corresponding tracepoint_user is not found. */
+	tuser = __tracepoint_user_init(name, tpoint);
+	if (!IS_ERR_OR_NULL(tuser))
+		*pmod = no_free_ptr(mod);
+
+	return tuser;
 }
 
-static const char *tracepoint_user_lookup(struct tracepoint_user *tuser, char *buf)
+static void tracepoint_user_put(struct tracepoint_user *tuser)
 {
-	struct tracepoint *tpoint = tuser->tpoint;
+	scoped_guard(mutex, &tracepoint_user_mutex) {
+		if (--tuser->refcount > 0)
+			return;
 
-	if (!tpoint)
-		return NULL;
+		list_del(&tuser->list);
+		tracepoint_user_unregister(tuser);
+	}
 
-	return kallsyms_lookup((unsigned long)tpoint->probestub, NULL, NULL, NULL, buf);
+	__tracepoint_user_free(tuser);
 }
 
+DEFINE_FREE(tuser_put, struct tracepoint_user *,
+	if (!IS_ERR_OR_NULL(_T))
+		tracepoint_user_put(_T))
+
 /*
  * Fprobe event core functions
  */
+
+/*
+ * @tprobe is true for tracepoint probe.
+ * @tuser can be NULL if the trace_fprobe is disabled or the tracepoint is not
+ * loaded with a module. If @tuser != NULL, this trace_fprobe is enabled.
+ */
 struct trace_fprobe {
 	struct dyn_event	devent;
 	struct fprobe		fp;
 	const char		*symbol;
+	bool			tprobe;
 	struct tracepoint_user	*tuser;
 	struct trace_probe	tp;
 };
@@ -157,7 +218,7 @@ static bool trace_fprobe_is_return(struct trace_fprobe *tf)
 
 static bool trace_fprobe_is_tracepoint(struct trace_fprobe *tf)
 {
-	return tf->tuser != NULL;
+	return tf->tprobe;
 }
 
 static const char *trace_fprobe_symbol(struct trace_fprobe *tf)
@@ -207,56 +268,6 @@ static bool trace_fprobe_is_registered(struct trace_fprobe *tf)
 	return fprobe_is_registered(&tf->fp);
 }
 
-static struct tracepoint *find_tracepoint(const char *tp_name,
-	struct module **tp_mod);
-
-/*
- * Get tracepoint_user if exist, or allocate new one. If tracepoint is on a
- * module, get its refcounter.
- */
-static struct tracepoint_user *
-trace_fprobe_get_tracepoint_user(const char *name, struct module **pmod)
-{
-	struct tracepoint_user *tuser __free(kfree) = NULL;
-	struct tracepoint *tpoint;
-	struct trace_fprobe *tf;
-	struct dyn_event *dpos;
-	struct module *mod __free(module_put) = NULL;
-	int ret;
-
-	/*
-	 * Find appropriate tracepoint and locking module.
-	 * Note: tpoint can be NULL if it is unloaded (or failed to get module.)
-	 */
-	tpoint = find_tracepoint(name, &mod);
-
-	/* Search existing tracepoint_user */
-	for_each_trace_fprobe(tf, dpos) {
-		if (!trace_fprobe_is_tracepoint(tf))
-			continue;
-		if (!strcmp(tf->symbol, name)) {
-			tracepoint_user_get(tf->tuser);
-			*pmod = no_free_ptr(mod);
-			return tf->tuser;
-		}
-	}
-
-	/* Not found, allocate and register new tracepoint_user. */
-	tuser = tracepoint_user_allocate(tpoint);
-	if (!tuser)
-		return NULL;
-
-	if (tpoint) {
-		/* If the tracepoint is not loaded, tpoint can be NULL. */
-		ret = tracepoint_user_register(tuser);
-		if (ret)
-			return ERR_PTR(ret);
-	}
-
-	*pmod = no_free_ptr(mod);
-	return_ptr(tuser);
-}
-
 /*
  * Note that we don't verify the fetch_insn code, since it does not come
  * from user space.
@@ -558,8 +569,8 @@ DEFINE_FREE(free_trace_fprobe, struct trace_fprobe *, if (!IS_ERR_OR_NULL(_T)) f
 static struct trace_fprobe *alloc_trace_fprobe(const char *group,
 					       const char *event,
 					       const char *symbol,
-					       struct tracepoint_user *tuser,
-					       int nargs, bool is_return)
+					       int nargs, bool is_return,
+					       bool is_tracepoint)
 {
 	struct trace_fprobe *tf __free(free_trace_fprobe) = NULL;
 	int ret = -ENOMEM;
@@ -577,7 +588,7 @@ static struct trace_fprobe *alloc_trace_fprobe(const char *group,
 	else
 		tf->fp.entry_handler = fentry_dispatcher;
 
-	tf->tuser = tuser;
+	tf->tprobe = is_tracepoint;
 
 	ret = trace_probe_init(&tf->tp, event, group, false, nargs);
 	if (ret < 0)
@@ -751,12 +762,35 @@ static int unregister_fprobe_event(struct trace_fprobe *tf)
 
 static int __regsiter_tracepoint_fprobe(struct trace_fprobe *tf)
 {
-	unsigned long ip = tracepoint_user_ip(tf->tuser);
+	struct tracepoint_user *tuser __free(tuser_put) = NULL;
+	struct module *mod __free(module_put) = NULL;
+	unsigned long ip;
+	int ret;
 
-	if (!ip)
-		return -ENOENT;
+	if (WARN_ON_ONCE(tf->tuser))
+		return -EINVAL;
+
+	/* If the tracepoint is in a module, it must be locked in this function. */
+	tuser = tracepoint_user_find_get(tf->symbol, &mod);
+	/* This tracepoint is not loaded yet */
+	if (IS_ERR(tuser))
+		return PTR_ERR(tuser);
+	if (!tuser)
+		return -ENOMEM;
 
-	return register_fprobe_ips(&tf->fp, &ip, 1);
+	/* Register fprobe only if the tracepoint is loaded. */
+	if (tuser->tpoint) {
+		ip = tracepoint_user_ip(tuser);
+		if (WARN_ON_ONCE(!ip))
+			return -ENOENT;
+
+		ret = register_fprobe_ips(&tf->fp, &ip, 1);
+		if (ret < 0)
+			return ret;
+	}
+
+	tf->tuser = no_free_ptr(tuser);
+	return 0;
 }
 
 /* Returns an error if the target function is not available, or 0 */
@@ -764,15 +798,9 @@ static int trace_fprobe_verify_target(struct trace_fprobe *tf)
 {
 	int ret;
 
-	if (trace_fprobe_is_tracepoint(tf)) {
-
-		/* This tracepoint is not loaded yet */
-		if (!tracepoint_user_is_registered(tf->tuser))
-			return 0;
-
-		/* We assume all stab function is tracable. */
-		return tracepoint_user_ip(tf->tuser) ? 0 : -ENOENT;
-	}
+	/* Tracepoint should have a stub function. */
+	if (trace_fprobe_is_tracepoint(tf))
+		return 0;
 
 	/*
 	 * Note: since we don't lock the module, even if this succeeded,
@@ -803,14 +831,8 @@ static int __register_trace_fprobe(struct trace_fprobe *tf)
 
 	tf->fp.flags &= ~FPROBE_FL_DISABLED;
 
-	if (trace_fprobe_is_tracepoint(tf)) {
-
-		/* This tracepoint is not loaded yet */
-		if (!tracepoint_user_is_registered(tf->tuser))
-			return 0;
-
+	if (trace_fprobe_is_tracepoint(tf))
 		return __regsiter_tracepoint_fprobe(tf);
-	}
 
 	/* TODO: handle filter, nofilter or symbol list */
 	return register_fprobe(&tf->fp, tf->symbol, NULL);
@@ -819,11 +841,9 @@ static int __register_trace_fprobe(struct trace_fprobe *tf)
 /* Internal unregister function - just handle fprobe and flags */
 static void __unregister_trace_fprobe(struct trace_fprobe *tf)
 {
-	if (trace_fprobe_is_registered(tf)) {
+	if (trace_fprobe_is_registered(tf))
 		unregister_fprobe(&tf->fp);
-		memset(&tf->fp, 0, sizeof(tf->fp));
-	}
-	if (trace_fprobe_is_tracepoint(tf)) {
+	if (tf->tuser) {
 		tracepoint_user_put(tf->tuser);
 		tf->tuser = NULL;
 	}
@@ -1027,63 +1047,52 @@ static struct tracepoint *find_tracepoint_in_module(struct module *mod,
 	return data.tpoint;
 }
 
+/* These are CONFIG_MODULES=y specific functions. */
+static bool tracepoint_user_within_module(struct tracepoint_user *tuser,
+					  struct module *mod)
+{
+	return within_module(tracepoint_user_ip(tuser), mod);
+}
+
+static int tracepoint_user_register_again(struct tracepoint_user *tuser,
+					  struct tracepoint *tpoint)
+{
+	tuser->tpoint = tpoint;
+	return tracepoint_user_register(tuser);
+}
+
+static void tracepoint_user_unregister_clear(struct tracepoint_user *tuser)
+{
+	tracepoint_user_unregister(tuser);
+	tuser->tpoint = NULL;
+}
+
+/* module callback for tracepoint_user */
 static int __tracepoint_probe_module_cb(struct notifier_block *self,
 					unsigned long val, void *data)
 {
 	struct tp_module *tp_mod = data;
 	struct tracepoint_user *tuser;
-	struct trace_fprobe *tf;
-	struct dyn_event *pos;
+	struct tracepoint *tpoint;
 
 	if (val != MODULE_STATE_GOING && val != MODULE_STATE_COMING)
 		return NOTIFY_DONE;
 
-	mutex_lock(&event_mutex);
-	for_each_trace_fprobe(tf, pos) {
-		if (!trace_fprobe_is_tracepoint(tf))
-			continue;
-
+	mutex_lock(&tracepoint_user_mutex);
+	for_each_tracepoint_user(tuser) {
 		if (val == MODULE_STATE_COMING) {
-			/*
-			 * If any tracepoint used by tprobe is in the module,
-			 * register the stub.
-			 */
-			struct tracepoint *tpoint;
-
-			tpoint = find_tracepoint_in_module(tp_mod->mod, tf->symbol);
 			/* This is not a tracepoint in this module. Skip it. */
+			tpoint = find_tracepoint_in_module(tp_mod->mod, tuser->name);
 			if (!tpoint)
 				continue;
-
-			tuser = tf->tuser;
-			/* If the tracepoint is not registered yet, register it. */
-			if (!tracepoint_user_is_registered(tuser)) {
-				tuser->tpoint = tpoint;
-				if (WARN_ON_ONCE(tracepoint_user_register(tuser)))
-					continue;
-			}
-
-			/* Finally enable fprobe on this module. */
-			if (trace_probe_is_enabled(&tf->tp) && !trace_fprobe_is_registered(tf))
-				WARN_ON_ONCE(__regsiter_tracepoint_fprobe(tf));
-		} else if (val == MODULE_STATE_GOING) {
-			tuser = tf->tuser;
+			WARN_ON_ONCE(tracepoint_user_register_again(tuser, tpoint));
+		} else if (val == MODULE_STATE_GOING &&
+			  tracepoint_user_within_module(tuser, tp_mod->mod)) {
 			/* Unregister all tracepoint_user in this module. */
-			if (tracepoint_user_is_registered(tuser) &&
-			    tracepoint_user_within_module(tuser, tp_mod->mod))
-				tracepoint_user_unregister(tuser);
-
-			/*
-			 * Here we need to handle shared tracepoint_user case.
-			 * Such tuser is unregistered, but trace_fprobe itself
-			 * is registered. (Note this only handles tprobes.)
-			 */
-			if (!tracepoint_user_is_registered(tuser) &&
-			    trace_fprobe_is_registered(tf))
-				unregister_fprobe(&tf->fp);
+			tracepoint_user_unregister_clear(tuser);
 		}
 	}
-	mutex_unlock(&event_mutex);
+	mutex_unlock(&tracepoint_user_mutex);
 
 	return NOTIFY_DONE;
 }
@@ -1091,6 +1100,54 @@ static int __tracepoint_probe_module_cb(struct notifier_block *self,
 static struct notifier_block tracepoint_module_nb = {
 	.notifier_call = __tracepoint_probe_module_cb,
 };
+
+/* module callback for tprobe events */
+static int __tprobe_event_module_cb(struct notifier_block *self,
+				     unsigned long val, void *data)
+{
+	struct trace_fprobe *tf;
+	struct dyn_event *pos;
+	struct module *mod = data;
+
+	if (val != MODULE_STATE_GOING && val != MODULE_STATE_COMING)
+		return NOTIFY_DONE;
+
+	mutex_lock(&event_mutex);
+	for_each_trace_fprobe(tf, pos) {
+		/* Skip fprobe and disabled tprobe events. */
+		if (!trace_fprobe_is_tracepoint(tf) || !tf->tuser)
+			continue;
+
+		/* Before this notification, tracepoint notifier has already done. */
+		if (val == MODULE_STATE_COMING &&
+		    tracepoint_user_within_module(tf->tuser, mod)) {
+			unsigned long ip = tracepoint_user_ip(tf->tuser);
+
+			WARN_ON_ONCE(register_fprobe_ips(&tf->fp, &ip, 1));
+		} else if (val == MODULE_STATE_GOING &&
+			   /*
+			    * tracepoint_user_within_module() does not work here because
+			    * tracepoint_user is already unregistered and cleared tpoint.
+			    * Instead, checking whether the fprobe is registered but
+			    * tpoint is cleared(unregistered). Such unbalance probes
+			    * must be adjusted anyway.
+			    */
+			    trace_fprobe_is_registered(tf) &&
+			    !tf->tuser->tpoint) {
+			unregister_fprobe(&tf->fp);
+		}
+	}
+	mutex_unlock(&event_mutex);
+
+	return NOTIFY_DONE;
+}
+
+/* NOTE: this must be called after tracepoint callback */
+static struct notifier_block tprobe_event_module_nb = {
+	.notifier_call = __tprobe_event_module_cb,
+	/* Make sure this is later than tracepoint module notifier. */
+	.priority = -10,
+};
 #endif /* CONFIG_MODULES */
 
 static int parse_symbol_and_return(int argc, const char *argv[],
@@ -1149,10 +1206,6 @@ static int parse_symbol_and_return(int argc, const char *argv[],
 	return 0;
 }
 
-DEFINE_FREE(tuser_put, struct tracepoint_user *,
-	if (!IS_ERR_OR_NULL(_T))
-		tracepoint_user_put(_T))
-
 static int trace_fprobe_create_internal(int argc, const char *argv[],
 					struct traceprobe_parse_context *ctx)
 {
@@ -1181,7 +1234,6 @@ static int trace_fprobe_create_internal(int argc, const char *argv[],
 	 *  FETCHARG:TYPE : use TYPE instead of unsigned long.
 	 */
 	struct trace_fprobe *tf __free(free_trace_fprobe) = NULL;
-	struct tracepoint_user *tuser __free(tuser_put) = NULL;
 	struct module *mod __free(module_put) = NULL;
 	int i, new_argc = 0, ret = 0;
 	bool is_return = false;
@@ -1244,21 +1296,19 @@ static int trace_fprobe_create_internal(int argc, const char *argv[],
 	else
 		ctx->flags |= TPARG_FL_FENTRY;
 
+	ctx->funcname = NULL;
 	if (is_tracepoint) {
+		/* Get tracepoint and lock its module until the end of the registration. */
+		struct tracepoint *tpoint;
+
 		ctx->flags |= TPARG_FL_TPOINT;
-		tuser = trace_fprobe_get_tracepoint_user(symbol, &mod);
-		if (!tuser)
-			return -ENOMEM;
-		if (IS_ERR(tuser)) {
-			trace_probe_log_set_index(1);
-			trace_probe_log_err(0, NO_TRACEPOINT);
-			return PTR_ERR(tuser);
-		}
-		ctx->funcname = tracepoint_user_lookup(tuser, sbuf);
-		/* If tracepoint is not loaded yet, use symbol name as funcname. */
-		if (!ctx->funcname)
-			ctx->funcname = symbol;
-	} else
+		mod = NULL;
+		tpoint = find_tracepoint(symbol, &mod);
+		if (tpoint)
+			ctx->funcname = kallsyms_lookup((unsigned long)tpoint->probestub,
+							NULL, NULL, NULL, sbuf);
+	}
+	if (!ctx->funcname)
 		ctx->funcname = symbol;
 
 	argc -= 2; argv += 2;
@@ -1278,14 +1328,13 @@ static int trace_fprobe_create_internal(int argc, const char *argv[],
 		return ret;
 
 	/* setup a probe */
-	tf = alloc_trace_fprobe(group, event, symbol, tuser, argc, is_return);
+	tf = alloc_trace_fprobe(group, event, symbol, argc, is_return, is_tracepoint);
 	if (IS_ERR(tf)) {
 		ret = PTR_ERR(tf);
 		/* This must return -ENOMEM, else there is a bug */
 		WARN_ON_ONCE(ret != -ENOMEM);
 		return ret;
 	}
-	tuser = NULL; /* Move tuser to tf. */
 
 	/* parse arguments */
 	for (i = 0; i < argc; i++) {
@@ -1503,6 +1552,9 @@ static __init int init_fprobe_trace_early(void)
 	ret = register_tracepoint_module_notifier(&tracepoint_module_nb);
 	if (ret)
 		return ret;
+	ret = register_module_notifier(&tprobe_event_module_nb);
+	if (ret)
+		return ret;
 #endif
 
 	return 0;