tracing/kprobes: Support module init function probing

To support probing module init functions, kprobe-tracer allows
user to define a probe on non-existed function when it is given
with a module name. This also enables user to set a probe on
a function on a specific module, even if a same name (but different)
function is locally defined in another module.

The module name must be in the front of function name and separated
by a ':'. e.g. btrfs:btrfs_init_sysfs

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lkml.kernel.org/r/20110627072656.6528.89970.stgit@fedora15
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 143 insertions, 30 deletions

diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
index c83bd6b4e6e..d0d0bb9e3e2 100644
--- a/Documentation/trace/kprobetrace.txt
+++ b/Documentation/trace/kprobetrace.txt
@@ -22,14 +22,15 @@ current_tracer. Instead of that, add probe points via
 
 Synopsis of kprobe_events
 -------------------------
-  p[:[GRP/]EVENT] SYMBOL[+offs]|MEMADDR [FETCHARGS]     : Set a probe
-  r[:[GRP/]EVENT] SYMBOL[+0] [FETCHARGS]                : Set a return probe
+  p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS]  : Set a probe
+  r[:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS]             : Set a return probe
   -:[GRP/]EVENT                                         : Clear a probe
 
  GRP            : Group name. If omitted, use "kprobes" for it.
  EVENT          : Event name. If omitted, the event name is generated
-                  based on SYMBOL+offs or MEMADDR.
- SYMBOL[+offs]  : Symbol+offset where the probe is inserted.
+                  based on SYM+offs or MEMADDR.
+ MOD            : Module name which has given SYM.
+ SYM[+offs]     : Symbol+offset where the probe is inserted.
  MEMADDR        : Address where the probe is inserted.
 
  FETCHARGS      : Arguments. Each probe can have up to 128 args.
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 3be50c52d08..acc6664a6b2 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -536,6 +536,7 @@ struct probe_arg {
 /* Flags for trace_probe */
 #define TP_FLAG_TRACE   1
 #define TP_FLAG_PROFILE 2
+#define TP_FLAG_REGISTERED 4
 
 struct trace_probe {
         struct list_head        list;
@@ -565,6 +566,39 @@ static __kprobes const char *trace_probe_symbol(struct trace_probe *tp)
         return tp->symbol ? tp->symbol : "unknown";
 }
 
+static __kprobes unsigned long trace_probe_offset(struct trace_probe *tp)
+{
+        return tp->rp.kp.offset;
+}
+
+static __kprobes bool trace_probe_is_enabled(struct trace_probe *tp)
+{
+        return !!(tp->flags & (TP_FLAG_TRACE | TP_FLAG_PROFILE));
+}
+
+static __kprobes bool trace_probe_is_registered(struct trace_probe *tp)
+{
+        return !!(tp->flags & TP_FLAG_REGISTERED);
+}
+
+static __kprobes bool trace_probe_has_gone(struct trace_probe *tp)
+{
+        return !!(kprobe_gone(&tp->rp.kp));
+}
+
+static __kprobes bool trace_probe_within_module(struct trace_probe *tp,
+                                                struct module *mod)
+{
+        int len = strlen(mod->name);
+        const char *name = trace_probe_symbol(tp);
+        return strncmp(mod->name, name, len) == 0 && name[len] == ':';
+}
+
+static __kprobes bool trace_probe_is_on_module(struct trace_probe *tp)
+{
+        return !!strchr(trace_probe_symbol(tp), ':');
+}
+
 static int register_probe_event(struct trace_probe *tp);
 static void unregister_probe_event(struct trace_probe *tp);
 
@@ -689,7 +723,8 @@ static int enable_trace_probe(struct trace_probe *tp, int flag)
         int ret = 0;
 
         tp->flags |= flag;
-        if (tp->flags & (TP_FLAG_TRACE | TP_FLAG_PROFILE)) {
+        if (trace_probe_is_enabled(tp) && trace_probe_is_registered(tp) &&
+            !trace_probe_has_gone(tp)) {
                 if (trace_probe_is_return(tp))
                         ret = enable_kretprobe(&tp->rp);
                 else
@@ -703,7 +738,7 @@ static int enable_trace_probe(struct trace_probe *tp, int flag)
 static void disable_trace_probe(struct trace_probe *tp, int flag)
 {
         tp->flags &= ~flag;
-        if (!(tp->flags & (TP_FLAG_TRACE | TP_FLAG_PROFILE))) {
+        if (!trace_probe_is_enabled(tp) && trace_probe_is_registered(tp)) {
                 if (trace_probe_is_return(tp))
                         disable_kretprobe(&tp->rp);
                 else
@@ -711,13 +746,64 @@ static void disable_trace_probe(struct trace_probe *tp, int flag)
         }
 }
 
-/* Unregister a trace_probe and probe_event: call with locking probe_lock */
-static void unregister_trace_probe(struct trace_probe *tp)
+/* Internal register function - just handle k*probes and flags */
+static int __register_trace_probe(struct trace_probe *tp)
 {
+        int ret;
+
+        if (trace_probe_is_registered(tp))
+                return -EINVAL;
+
+        /* Set/clear disabled flag according to tp->flag */
+        if (trace_probe_is_enabled(tp))
+                tp->rp.kp.flags &= ~KPROBE_FLAG_DISABLED;
+        else
+                tp->rp.kp.flags |= KPROBE_FLAG_DISABLED;
+
         if (trace_probe_is_return(tp))
-                unregister_kretprobe(&tp->rp);
+                ret = register_kretprobe(&tp->rp);
         else
-                unregister_kprobe(&tp->rp.kp);
+                ret = register_kprobe(&tp->rp.kp);
+
+        if (ret == 0)
+                tp->flags |= TP_FLAG_REGISTERED;
+        else {
+                pr_warning("Could not insert probe at %s+%lu: %d\n",
+                           trace_probe_symbol(tp), trace_probe_offset(tp), ret);
+                if (ret == -ENOENT && trace_probe_is_on_module(tp)) {
+                        pr_warning("This probe might be able to register after"
+                                   "target module is loaded. Continue.\n");
+                        ret = 0;
+                } else if (ret == -EILSEQ) {
+                        pr_warning("Probing address(0x%p) is not an "
+                                   "instruction boundary.\n",
+                                   tp->rp.kp.addr);
+                        ret = -EINVAL;
+                }
+        }
+
+        return ret;
+}
+
+/* Internal unregister function - just handle k*probes and flags */
+static void __unregister_trace_probe(struct trace_probe *tp)
+{
+        if (trace_probe_is_registered(tp)) {
+                if (trace_probe_is_return(tp))
+                        unregister_kretprobe(&tp->rp);
+                else
+                        unregister_kprobe(&tp->rp.kp);
+                tp->flags &= ~TP_FLAG_REGISTERED;
+                /* Cleanup kprobe for reuse */
+                if (tp->rp.kp.symbol_name)
+                        tp->rp.kp.addr = NULL;
+        }
+}
+
+/* Unregister a trace_probe and probe_event: call with locking probe_lock */
+static void unregister_trace_probe(struct trace_probe *tp)
+{
+        __unregister_trace_probe(tp);
         list_del(&tp->list);
         unregister_probe_event(tp);
 }
@@ -730,41 +816,65 @@ static int register_trace_probe(struct trace_probe *tp)
 
         mutex_lock(&probe_lock);
 
-        /* register as an event */
+        /* Delete old (same name) event if exist */
         old_tp = find_trace_probe(tp->call.name, tp->call.class->system);
         if (old_tp) {
-                /* delete old event */
                 unregister_trace_probe(old_tp);
                 free_trace_probe(old_tp);
         }
+
+        /* Register new event */
         ret = register_probe_event(tp);
         if (ret) {
                 pr_warning("Failed to register probe event(%d)\n", ret);
                 goto end;
         }
 
-        tp->rp.kp.flags |= KPROBE_FLAG_DISABLED;
-        if (trace_probe_is_return(tp))
-                ret = register_kretprobe(&tp->rp);
-        else
-                ret = register_kprobe(&tp->rp.kp);
-
-        if (ret) {
-                pr_warning("Could not insert probe(%d)\n", ret);
-                if (ret == -EILSEQ) {
-                        pr_warning("Probing address(0x%p) is not an "
-                                   "instruction boundary.\n",
-                                   tp->rp.kp.addr);
-                        ret = -EINVAL;
-                }
+        /* Register k*probe */
+        ret = __register_trace_probe(tp);
+        if (ret < 0)
                 unregister_probe_event(tp);
-        } else
+        else
                 list_add_tail(&tp->list, &probe_list);
+
 end:
         mutex_unlock(&probe_lock);
         return ret;
 }
 
+/* Module notifier call back, checking event on the module */
+static int trace_probe_module_callback(struct notifier_block *nb,
+                                       unsigned long val, void *data)
+{
+        struct module *mod = data;
+        struct trace_probe *tp;
+        int ret;
+
+        if (val != MODULE_STATE_COMING)
+                return NOTIFY_DONE;
+
+        /* Update probes on coming module */
+        mutex_lock(&probe_lock);
+        list_for_each_entry(tp, &probe_list, list) {
+                if (trace_probe_within_module(tp, mod)) {
+                        __unregister_trace_probe(tp);
+                        ret = __register_trace_probe(tp);
+                        if (ret)
+                                pr_warning("Failed to re-register probe %s on"
+                                           "%s: %d\n",
+                                           tp->call.name, mod->name, ret);
+                }
+        }
+        mutex_unlock(&probe_lock);
+
+        return NOTIFY_DONE;
+}
+
+static struct notifier_block trace_probe_module_nb = {
+        .notifier_call = trace_probe_module_callback,
+        .priority = 1   /* Invoked after kprobe module callback */
+};
+
 /* Split symbol and offset. */
 static int split_symbol_offset(char *symbol, unsigned long *offset)
 {
@@ -990,8 +1100,8 @@ static int create_trace_probe(int argc, char **argv)
 {
         /*
          * Argument syntax:
-         *  - Add kprobe: p[:[GRP/]EVENT] KSYM[+OFFS]|KADDR [FETCHARGS]
-         *  - Add kretprobe: r[:[GRP/]EVENT] KSYM[+0] [FETCHARGS]
+         *  - Add kprobe: p[:[GRP/]EVENT] [MOD:]KSYM[+OFFS]|KADDR [FETCHARGS]
+         *  - Add kretprobe: r[:[GRP/]EVENT] [MOD:]KSYM[+0] [FETCHARGS]
          * Fetch args:
          *  $retval     : fetch return value
          *  $stack      : fetch stack address
@@ -1186,7 +1296,6 @@ static void release_all_trace_probes(void)
         mutex_unlock(&probe_lock);
 }
 
-
 /* Probes listing interfaces */
 static void *probes_seq_start(struct seq_file *m, loff_t *pos)
 {
@@ -1827,6 +1936,9 @@ static __init int init_kprobe_trace(void)
         struct dentry *d_tracer;
         struct dentry *entry;
 
+        if (register_module_notifier(&trace_probe_module_nb))
+                return -EINVAL;
+
         d_tracer = tracing_init_dentry();
         if (!d_tracer)
                 return 0;