tracing: tprobe-events: Support multiple tprobes on the same tracepoint

Allow user to set multiple tracepoint-probe events on the same
tracepoint. After the last tprobe-event is removed, the tracepoint
callback is unregistered.

Link: https://lore.kernel.org/all/174343536245.843280.6548776576601537671.stgit@devnote2/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

diff --git a/include/linux/module.h b/include/linux/module.h
index 5faa1fb1f4b4d5cfe350b346cb1d8204885eea91..2cb5be5cc7e65ed6d002f2b10ec27465bf61438e 100644 (file)
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -14,6 +14,7 @@
 #include <linux/buildid.h>
 #include <linux/compiler.h>
 #include <linux/cache.h>
+#include <linux/cleanup.h>
 #include <linux/kmod.h>
 #include <linux/init.h>
 #include <linux/elf.h>
@@ -1019,4 +1020,7 @@ static inline unsigned long find_kallsyms_symbol_value(struct module *mod,
 
 #endif  /* CONFIG_MODULES && CONFIG_KALLSYMS */
 
+/* Define __free(module_put) macro for struct module *. */
+DEFINE_FREE(module_put, struct module *, if (_T) module_put(_T))
+
 #endif /* _LINUX_MODULE_H */

diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 017d6ebfdf8b63b35a770be6d5c5a334be867b19..4a9ce7b0e084877bc19faf971e1d01185270b263 100644 (file)
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -21,7 +21,6 @@
 #define FPROBE_EVENT_SYSTEM "fprobes"
 #define TRACEPOINT_EVENT_SYSTEM "tracepoints"
 #define RETHOOK_MAXACTIVE_MAX 4096
-#define TRACEPOINT_STUB ERR_PTR(-ENOENT)
 
 static int trace_fprobe_create(const char *raw_command);
 static int trace_fprobe_show(struct seq_file *m, struct dyn_event *ev);
@@ -38,6 +37,89 @@ static struct dyn_event_operations trace_fprobe_ops = {
        .match = trace_fprobe_match,
 };
 
+struct tracepoint_user {
+       struct tracepoint       *tpoint;
+       unsigned int            refcount;
+};
+
+static bool tracepoint_user_is_registered(struct tracepoint_user *tuser)
+{
+       return tuser && tuser->tpoint;
+}
+
+static int tracepoint_user_register(struct tracepoint_user *tuser)
+{
+       struct tracepoint *tpoint = tuser->tpoint;
+
+       if (!tpoint)
+               return 0;
+
+       return tracepoint_probe_register_prio_may_exist(tpoint,
+                                       tpoint->probestub, NULL, 0);
+}
+
+static void tracepoint_user_unregister(struct tracepoint_user *tuser)
+{
+       if (!tuser->tpoint)
+               return;
+
+       WARN_ON_ONCE(tracepoint_probe_unregister(tuser->tpoint, tuser->tpoint->probestub, NULL));
+       tuser->tpoint = NULL;
+}
+
+static unsigned long tracepoint_user_ip(struct tracepoint_user *tuser)
+{
+       if (!tuser->tpoint)
+               return 0UL;
+
+       return (unsigned long)tuser->tpoint->probestub;
+}
+
+static bool tracepoint_user_within_module(struct tracepoint_user *tuser,
+                                         struct module *mod)
+{
+       return within_module(tracepoint_user_ip(tuser), mod);
+}
+
+static struct tracepoint_user *tracepoint_user_allocate(struct tracepoint *tpoint)
+{
+       struct tracepoint_user *tuser;
+
+       tuser = kzalloc(sizeof(*tuser), GFP_KERNEL);
+       if (!tuser)
+               return NULL;
+       tuser->tpoint = tpoint;
+       tuser->refcount = 1;
+
+       return tuser;
+}
+
+/* These must be called with event_mutex */
+static void tracepoint_user_get(struct tracepoint_user *tuser)
+{
+       tuser->refcount++;
+}
+
+static void tracepoint_user_put(struct tracepoint_user *tuser)
+{
+       if (--tuser->refcount > 0)
+               return;
+
+       if (tracepoint_user_is_registered(tuser))
+               tracepoint_user_unregister(tuser);
+       kfree(tuser);
+}
+
+static const char *tracepoint_user_lookup(struct tracepoint_user *tuser, char *buf)
+{
+       struct tracepoint *tpoint = tuser->tpoint;
+
+       if (!tpoint)
+               return NULL;
+
+       return kallsyms_lookup((unsigned long)tpoint->probestub, NULL, NULL, NULL, buf);
+}
+
 /*
  * Fprobe event core functions
  */
@@ -45,7 +127,7 @@ struct trace_fprobe {
        struct dyn_event        devent;
        struct fprobe           fp;
        const char              *symbol;
-       struct tracepoint       *tpoint;
+       struct tracepoint_user  *tuser;
        struct trace_probe      tp;
 };
 
@@ -75,7 +157,7 @@ static bool trace_fprobe_is_return(struct trace_fprobe *tf)
 
 static bool trace_fprobe_is_tracepoint(struct trace_fprobe *tf)
 {
-       return tf->tpoint != NULL;
+       return tf->tuser != NULL;
 }
 
 static const char *trace_fprobe_symbol(struct trace_fprobe *tf)
@@ -125,6 +207,56 @@ 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.
@@ -410,6 +542,8 @@ static void free_trace_fprobe(struct trace_fprobe *tf)
 {
        if (tf) {
                trace_probe_cleanup(&tf->tp);
+               if (tf->tuser)
+                       tracepoint_user_put(tf->tuser);
                kfree(tf->symbol);
                kfree(tf);
        }
@@ -424,7 +558,7 @@ 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 *tpoint,
+                                              struct tracepoint_user *tuser,
                                               int nargs, bool is_return)
 {
        struct trace_fprobe *tf __free(free_trace_fprobe) = NULL;
@@ -443,7 +577,7 @@ static struct trace_fprobe *alloc_trace_fprobe(const char *group,
        else
                tf->fp.entry_handler = fentry_dispatcher;
 
-       tf->tpoint = tpoint;
+       tf->tuser = tuser;
 
        ret = trace_probe_init(&tf->tp, event, group, false, nargs);
        if (ret < 0)
@@ -709,19 +843,11 @@ static int unregister_fprobe_event(struct trace_fprobe *tf)
 
 static int __regsiter_tracepoint_fprobe(struct trace_fprobe *tf)
 {
-       struct tracepoint *tpoint = tf->tpoint;
-       unsigned long ip = (unsigned long)tpoint->probestub;
-       int ret;
+       unsigned long ip = tracepoint_user_ip(tf->tuser);
+
+       if (!ip)
+               return -ENOENT;
 
-       /*
-        * Here, we do 2 steps to enable fprobe on a tracepoint.
-        * At first, put __probestub_##TP function on the tracepoint
-        * and put a fprobe on the stub function.
-        */
-       ret = tracepoint_probe_register_prio_may_exist(tpoint,
-                               tpoint->probestub, NULL, 0);
-       if (ret < 0)
-               return ret;
        return register_fprobe_ips(&tf->fp, &ip, 1);
 }
 
@@ -753,7 +879,7 @@ static int __register_trace_fprobe(struct trace_fprobe *tf)
        if (trace_fprobe_is_tracepoint(tf)) {
 
                /* This tracepoint is not loaded yet */
-               if (tf->tpoint == TRACEPOINT_STUB)
+               if (!tracepoint_user_is_registered(tf->tuser))
                        return 0;
 
                return __regsiter_tracepoint_fprobe(tf);
@@ -770,9 +896,8 @@ static void __unregister_trace_fprobe(struct trace_fprobe *tf)
                unregister_fprobe(&tf->fp);
                memset(&tf->fp, 0, sizeof(tf->fp));
                if (trace_fprobe_is_tracepoint(tf)) {
-                       tracepoint_probe_unregister(tf->tpoint,
-                                       tf->tpoint->probestub, NULL);
-                       tf->tpoint = NULL;
+                       tracepoint_user_put(tf->tuser);
+                       tf->tuser = NULL;
                }
        }
 }
@@ -988,7 +1113,7 @@ static int __tracepoint_probe_module_cb(struct notifier_block *self,
                                        unsigned long val, void *data)
 {
        struct tp_module *tp_mod = data;
-       struct tracepoint *tpoint;
+       struct tracepoint_user *tuser;
        struct trace_fprobe *tf;
        struct dyn_event *pos;
 
@@ -999,21 +1124,46 @@ static int __tracepoint_probe_module_cb(struct notifier_block *self,
        for_each_trace_fprobe(tf, pos) {
                if (!trace_fprobe_is_tracepoint(tf))
                        continue;
-               if (val == MODULE_STATE_COMING && tf->tpoint == TRACEPOINT_STUB) {
+
+               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);
-                       if (tpoint) {
-                               tf->tpoint = tpoint;
-                               if (!WARN_ON_ONCE(__regsiter_tracepoint_fprobe(tf)) &&
-                                   trace_probe_is_enabled(&tf->tp))
-                                       reenable_trace_fprobe(tf);
+                       /* This is not a tracepoint in this module. Skip it. */
+                       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;
                        }
-               } else if (val == MODULE_STATE_GOING &&
-                          tf->tpoint != TRACEPOINT_STUB &&
-                          within_module((unsigned long)tf->tpoint->probestub, tp_mod->mod)) {
-                       unregister_fprobe(&tf->fp);
-                       tracepoint_probe_unregister(tf->tpoint,
-                               tf->tpoint->probestub, NULL);
-                       tf->tpoint = TRACEPOINT_STUB;
+
+                       /* Finally enable fprobe on this module. */
+                       if (!WARN_ON_ONCE(__regsiter_tracepoint_fprobe(tf)) &&
+                           trace_probe_is_enabled(&tf->tp))
+                               reenable_trace_fprobe(tf);
+               } else if (val == MODULE_STATE_GOING) {
+                       tuser = tf->tuser;
+                       /* 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);
                }
        }
        mutex_unlock(&event_mutex);
@@ -1082,7 +1232,9 @@ static int parse_symbol_and_return(int argc, const char *argv[],
        return 0;
 }
 
-DEFINE_FREE(module_put, struct module *, if (_T) module_put(_T))
+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)
@@ -1112,6 +1264,8 @@ 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;
        char *symbol __free(kfree) = NULL;
@@ -1123,8 +1277,6 @@ static int trace_fprobe_create_internal(int argc, const char *argv[],
        char abuf[MAX_BTF_ARGS_LEN];
        char *dbuf __free(kfree) = NULL;
        bool is_tracepoint = false;
-       struct module *tp_mod __free(module_put) = NULL;
-       struct tracepoint *tpoint = NULL;
 
        if ((argv[0][0] != 'f' && argv[0][0] != 't') || argc < 2)
                return -ECANCELED;
@@ -1177,20 +1329,18 @@ static int trace_fprobe_create_internal(int argc, const char *argv[],
 
        if (is_tracepoint) {
                ctx->flags |= TPARG_FL_TPOINT;
-               tpoint = find_tracepoint(symbol, &tp_mod);
-               if (tpoint) {
-                       ctx->funcname = kallsyms_lookup(
-                               (unsigned long)tpoint->probestub,
-                               NULL, NULL, NULL, sbuf);
-               } else if (IS_ENABLED(CONFIG_MODULES)) {
-                               /* This *may* be loaded afterwards */
-                               tpoint = TRACEPOINT_STUB;
-                               ctx->funcname = symbol;
-               } else {
+               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 -EINVAL;
+                       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
                ctx->funcname = symbol;
 
@@ -1214,13 +1364,14 @@ static int trace_fprobe_create_internal(int argc, const char *argv[],
                return ret;
 
        /* setup a probe */
-       tf = alloc_trace_fprobe(group, event, symbol, tpoint, argc, is_return);
+       tf = alloc_trace_fprobe(group, event, symbol, tuser, argc, is_return);
        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++) {