linux-kernel - [PATCH v3] kernel/trace: Fix cleanup logic of enable_trace

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Date:   Mon,  3 Jul 2023 07:28:53 +0300
From:   "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@...il.com>
To:     rostedt@...dmis.org
Cc:     mhiramat@...nel.org, dan.carpenter@...aro.org,
        linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] kernel/trace: Fix cleanup logic of enable_trace_eprobe

The enable_trace_eprobe() function enables all event probes, attached
to given trace probe. If an error occurs in enabling one of the event
probes, all others should be roll backed. There is a bug in that roll
back logic - instead of all event probes, only the failed one is
disabled.

Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
Fixes: 7491e2c44278 ("tracing: Add a probe that attaches to trace events")
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@...il.com>
---
Changes since v1: https://lore.kernel.org/all/20230628121811.338655-1-tz.stoyanov@gmail.com/
 - Added one-time warning, suggested by Steven Rostedt.
Changed since v2: https://lore.kernel.org/lkml/20230630121627.833560-1-tz.stoyanov@gmail.com/
 - Added counter of successfully enabled eprobes, suggested by Steven Rostedt.

 kernel/trace/trace_eprobe.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index cb0077ba2b49..a0a704ba27db 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -644,6 +644,7 @@ static int enable_trace_eprobe(struct trace_event_call *call,
 	struct trace_eprobe *ep;
 	bool enabled;
 	int ret = 0;
+	int cnt = 0;
 
 	tp = trace_probe_primary_from_call(call);
 	if (WARN_ON_ONCE(!tp))
@@ -667,12 +668,25 @@ static int enable_trace_eprobe(struct trace_event_call *call,
 		if (ret)
 			break;
 		enabled = true;
+		cnt++;
 	}
 
 	if (ret) {
 		/* Failed to enable one of them. Roll back all */
-		if (enabled)
-			disable_eprobe(ep, file->tr);
+		if (enabled) {
+			/*
+			 * It's a bug if one failed for something other than memory
+			 * not being available but another eprobe succeeded.
+			 */
+			WARN_ON_ONCE(ret != -ENOMEM);
+
+			list_for_each_entry(pos, trace_probe_probe_list(tp), list) {
+				ep = container_of(pos, struct trace_eprobe, tp);
+				disable_eprobe(ep, file->tr);
+				if (!--cnt)
+					break;
+			}
+		}
 		if (file)
 			trace_probe_remove_file(tp, file);
 		else
-- 
2.41.0