linux-kernel - [PATCH] tracing/net_sched: Fix tracepoints that save qdisc

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Date: Thu, 29 Feb 2024 14:34:44 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Cong Wang <xiyou.wangcong@...il.com>,
 vaclav.zindulka@...pnet.cz, Jamal Hadi Salim  <jhs@...atatu.com>, Jiri
 Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>
Subject: [PATCH] tracing/net_sched: Fix tracepoints that save qdisc_dev() as
 a string

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

I'm updating __assign_str() and will be removing the second parameter. To
make sure that it does not break anything, I make sure that it matches the
__string() field, as that is where the string is actually going to be
saved in. To make sure there's nothing that breaks, I added a WARN_ON() to
make sure that what was used in __string() is the same that is used in
__assign_str().

In doing this change, an error was triggered as __assign_str() now expects
the string passed in to be a char * value. I instead had the following
warning:

include/trace/events/qdisc.h: In function ‘trace_event_raw_event_qdisc_reset’:
include/trace/events/qdisc.h:91:35: error: passing argument 1 of 'strcmp' from incompatible pointer type [-Werror=incompatible-pointer-types]
   91 |                 __assign_str(dev, qdisc_dev(q));

That's because the qdisc_enqueue() and qdisc_reset() pass in qdisc_dev(q)
to __assign_str() and to __string(). But that function returns a pointer
to struct net_device and not a string.

It appears that these events are just saving the pointer as a string and
then reading it as a string as well.

Use qdisc_dev(q)->name to save the device instead.

Fixes: a34dac0b90552 ("net_sched: add tracepoints for qdisc_reset() and qdisc_destroy()")
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 include/trace/events/qdisc.h | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/trace/events/qdisc.h b/include/trace/events/qdisc.h
index a3995925cb05..1f4258308b96 100644
--- a/include/trace/events/qdisc.h
+++ b/include/trace/events/qdisc.h
@@ -81,14 +81,14 @@ TRACE_EVENT(qdisc_reset,
 	TP_ARGS(q),

 	TP_STRUCT__entry(
-		__string(	dev,		qdisc_dev(q)	)
-		__string(	kind,		q->ops->id	)
-		__field(	u32,		parent		)
-		__field(	u32,		handle		)
+		__string(	dev,		qdisc_dev(q)->name	)
+		__string(	kind,		q->ops->id		)
+		__field(	u32,		parent			)
+		__field(	u32,		handle			)
 	),

 	TP_fast_assign(
-		__assign_str(dev, qdisc_dev(q));
+		__assign_str(dev, qdisc_dev(q)->name);
 		__assign_str(kind, q->ops->id);
 		__entry->parent = q->parent;
 		__entry->handle = q->handle;
@@ -106,14 +106,14 @@ TRACE_EVENT(qdisc_destroy,
 	TP_ARGS(q),

 	TP_STRUCT__entry(
-		__string(	dev,		qdisc_dev(q)	)
-		__string(	kind,		q->ops->id	)
-		__field(	u32,		parent		)
-		__field(	u32,		handle		)
+		__string(	dev,		qdisc_dev(q)->name	)
+		__string(	kind,		q->ops->id		)
+		__field(	u32,		parent			)
+		__field(	u32,		handle			)
 	),

 	TP_fast_assign(
-		__assign_str(dev, qdisc_dev(q));
+		__assign_str(dev, qdisc_dev(q)->name);
 		__assign_str(kind, q->ops->id);
 		__entry->parent = q->parent;
 		__entry->handle = q->handle;
-- 
2.43.0