[for-linus][PATCH 4/4] tracing/boottime: Fix kprobe multiple events

[Steven Rostedt <rostedt@goodmis.org>]

From: Sascha Ortmann <sascha.ortmann@stud.uni-hannover.de>

Fix boottime kprobe events to report and abort after each failure when
adding probes.

As an example, when we try to set multiprobe kprobe events in
bootconfig like this:

ftrace.event.kprobes.vfsevents {
        probes = "vfs_read $arg1 $arg2,,
                 !error! not reported;?", // leads to error
                 "vfs_write $arg1 $arg2"
}

This will not work as expected. After
commit da0f1f4167e3af69e ("tracing/boottime: Fix kprobe event API usage"),
the function trace_boot_add_kprobe_event will not produce any error
message when adding a probe fails at kprobe_event_gen_cmd_start.
Furthermore, we continue to add probes when kprobe_event_gen_cmd_end fails
(and kprobe_event_gen_cmd_start did not fail). In this case the function
even returns successfully when the last call to kprobe_event_gen_cmd_end
is successful.

The behaviour of reporting and aborting after failures is not
consistent.

The function trace_boot_add_kprobe_event now reports each failure and
stops adding probes immediately.

Link: https://lkml.kernel.org/r/20200618163301.25854-1-sascha.ortmann@stud.uni-hannover.de

Cc: stable@vger.kernel.org
Cc: linux-kernel@i4.cs.fau.de
Co-developed-by: Maximilian Werner <maximilian.werner96@gmail.com>
Fixes: da0f1f4167e3 ("tracing/boottime: Fix kprobe event API usage")
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Maximilian Werner <maximilian.werner96@gmail.com>
Signed-off-by: Sascha Ortmann <sascha.ortmann@stud.uni-hannover.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_boot.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index 8b5490cb02bb..fa0fc08c6ef8 100644
--- a/kernel/trace/trace_boot.c
+++ b/kernel/trace/trace_boot.c
@@ -101,12 +101,16 @@ trace_boot_add_kprobe_event(struct xbc_node *node, const char *event)
 		kprobe_event_cmd_init(&cmd, buf, MAX_BUF_LEN);
 
 		ret = kprobe_event_gen_cmd_start(&cmd, event, val);
-		if (ret)
+		if (ret) {
+			pr_err("Failed to generate probe: %s\n", buf);
 			break;
+		}
 
 		ret = kprobe_event_gen_cmd_end(&cmd);
-		if (ret)
+		if (ret) {
 			pr_err("Failed to add probe: %s\n", buf);
+			break;
+		}
 	}
 
 	return ret;
-- 
2.26.2