tracing: Fix event probe removal from dynamic events

When an event probe is to be removed via the API that created it via the
dynamic events, an -ENOENT error is returned.

This is because the removal of the event probe does not expect to see the
event system and name that the event probe is attached to, even though
that's part of the API to create it. As the removal of probes is to use
the same API as they are created.

In fact, the removal is not consistent with the kprobes and uprobes
removal. Fix that by allowing various ways to remove the eprobe.

The eprobe is created with:

 e:[GROUP/]NAME SYSTEM/EVENT [OPTIONS]

Have it get removed by echoing in the following into dynamic_events:

 # Remove all eprobes with NAME
 echo '-:NAME' >> dynamic_events

 # Remove a specific eprobe
 echo '-:GROUP/NAME' >> dynamic_events
 echo '-:GROUP/NAME SYSTEM/EVENT' >> dynamic_events
 echo '-:NAME SYSTEM/EVENT' >> dynamic_events
 echo '-:GROUP/NAME SYSTEM/EVENT OPTIONS' >> dynamic_events
 echo '-:NAME SYSTEM/EVENT OPTIONS' >> dynamic_events

Link: https://lkml.kernel.org/r/20211012081925.0e19cc4f@gandalf.local.home
Link: https://lkml.kernel.org/r/20211013205533.630722129@goodmis.orgSuggested-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 7491e2c4 ("tracing: Add a probe that attaches to trace events")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_eprobe.c

@@ -119,10 +119,58 @@ static bool eprobe_dyn_event_match(const char *system, const char *event,
 			int argc, const char **argv, struct dyn_event *ev)
 {
 	struct trace_eprobe *ep = to_trace_eprobe(ev);
+	const char *slash;
 
-	return strcmp(trace_probe_name(&ep->tp), event) == 0 &&
-	    (!system || strcmp(trace_probe_group_name(&ep->tp), system) == 0) &&
-	    trace_probe_match_command_args(&ep->tp, argc, argv);
+	/*
+	 * We match the following:
+	 *  event only			- match all eprobes with event name
+	 *  system and event only	- match all system/event probes
+	 *
+	 * The below has the above satisfied with more arguments:
+	 *
+	 *  attached system/event	- If the arg has the system and event
+	 *				  the probe is attached to, match
+	 *				  probes with the attachment.
+	 *
+	 *  If any more args are given, then it requires a full match.
+	 */
+
+	/*
+	 * If system exists, but this probe is not part of that system
+	 * do not match.
+	 */
+	if (system && strcmp(trace_probe_group_name(&ep->tp), system) != 0)
+		return false;
+
+	/* Must match the event name */
+	if (strcmp(trace_probe_name(&ep->tp), event) != 0)
+		return false;
+
+	/* No arguments match all */
+	if (argc < 1)
+		return true;
+
+	/* First argument is the system/event the probe is attached to */
+
+	slash = strchr(argv[0], '/');
+	if (!slash)
+		slash = strchr(argv[0], '.');
+	if (!slash)
+		return false;
+
+	if (strncmp(ep->event_system, argv[0], slash - argv[0]))
+		return false;
+	if (strcmp(ep->event_name, slash + 1))
+		return false;
+
+	argc--;
+	argv++;
+
+	/* If there are no other args, then match */
+	if (argc < 1)
+		return true;
+
+	return trace_probe_match_command_args(&ep->tp, argc, argv);
 }
 
 static struct dyn_event_operations eprobe_dyn_event_ops = {