linux-kernel - [PATCH 2/3] tracing/boottime: Fix kprobe event API usage

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Date:   Sat, 25 Apr 2020 14:49:17 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 2/3] tracing/boottime: Fix kprobe event API usage

Fix boottime kprobe events to use API correctly for
multiple events.

For example, when we set a multiprobe kprobe events in
bootconfig like below,

  ftrace.event.kprobes.myevent {
  	probes = "vfs_read $arg1 $arg2", "vfs_write $arg1 $arg2"
  }

This cause an error;

  trace_boot: Failed to add probe: p:kprobes/myevent (null)  vfs_read $arg1 $arg2  vfs_write $arg1 $arg2

This shows the 1st argument becomes NULL and multiprobes
are merged to 1 probe.

Fixes: 29a154810546 ("tracing: Change trace_boot to use kprobe_event interface")
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: stable@...r.kernel.org
---
 kernel/trace/trace_boot.c |   20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index 06d7feb5255f..9de29bb45a27 100644
--- a/kernel/trace/trace_boot.c
+++ b/kernel/trace/trace_boot.c
@@ -95,24 +95,20 @@ trace_boot_add_kprobe_event(struct xbc_node *node, const char *event)
 	struct xbc_node *anode;
 	char buf[MAX_BUF_LEN];
 	const char *val;
-	int ret;
+	int ret = 0;
 
-	kprobe_event_cmd_init(&cmd, buf, MAX_BUF_LEN);
+	xbc_node_for_each_array_value(node, "probes", anode, val) {
+		kprobe_event_cmd_init(&cmd, buf, MAX_BUF_LEN);
 
-	ret = kprobe_event_gen_cmd_start(&cmd, event, NULL);
-	if (ret)
-		return ret;
+		ret = kprobe_event_gen_cmd_start(&cmd, event, val);
+		if (ret)
+			break;
 
-	xbc_node_for_each_array_value(node, "probes", anode, val) {
-		ret = kprobe_event_add_field(&cmd, val);
+		ret = kprobe_event_gen_cmd_end(&cmd);
 		if (ret)
-			return ret;
+			pr_err("Failed to add probe: %s\n", buf);
 	}
 
-	ret = kprobe_event_gen_cmd_end(&cmd);
-	if (ret)
-		pr_err("Failed to add probe: %s\n", buf);
-
 	return ret;
 }
 #else