linux-kernel - Re: [PATCH] f2fs: Fix f2fs_truncate_partial

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Date:   Mon, 6 Mar 2023 12:25:29 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Douglas RAILLARD <douglas.raillard@....com>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net (open list:F2FS FILE SYSTEM),
        linux-kernel@...r.kernel.org (open list:TRACING),
        linux-trace-kernel@...r.kernel.org (open list:TRACING)
Subject: Re: [PATCH] f2fs: Fix f2fs_truncate_partial_nodes ftrace event

On Mon, 6 Mar 2023 11:15:13 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> > diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
> > index 31d994e6b4ca..8d053838d6cf 100644
> > --- a/include/trace/events/f2fs.h
> > +++ b/include/trace/events/f2fs.h
> > @@ -512,7 +512,7 @@ TRACE_EVENT(f2fs_truncate_partial_nodes,
> >  	TP_STRUCT__entry(
> >  		__field(dev_t,	dev)
> >  		__field(ino_t,	ino)
> > -		__field(nid_t,	nid[3])  
> 
> That should not have even compiled. I'll see if I can add some tricks to
> make that fail.

And this patch makes that happen!

-- Steve

diff --git a/include/trace/stages/stage5_get_offsets.h b/include/trace/stages/stage5_get_offsets.h
index ac5c24d3beeb..e30a13be46ba 100644
--- a/include/trace/stages/stage5_get_offsets.h
+++ b/include/trace/stages/stage5_get_offsets.h
@@ -9,17 +9,30 @@
 #undef __entry
 #define __entry entry
 
+/*
+ * Fields should never declare an array: i.e. __field(int, arr[5])
+ * If they do, it will cause issues in parsing and possibly corrupt the
+ * events. To prevent that from happening, test the sizeof() a fictitious
+ * type called "struct _test_no_array_##item" which will fail if "item"
+ * contains array elements (like "arr[5]").
+ *
+ * If you hit this, use __array(int, arr, 5) instead.
+ */
 #undef __field
-#define __field(type, item)
+#define __field(type, item)					\
+	{ (void)sizeof(struct _test_no_array_##item *); }
 
 #undef __field_ext
-#define __field_ext(type, item, filter_type)
+#define __field_ext(type, item, filter_type)			\
+	{ (void)sizeof(struct _test_no_array_##item *); }
 
 #undef __field_struct
-#define __field_struct(type, item)
+#define __field_struct(type, item)				\
+	{ (void)sizeof(struct _test_no_array_##item *); }
 
 #undef __field_struct_ext
-#define __field_struct_ext(type, item, filter_type)
+#define __field_struct_ext(type, item, filter_type)		\
+	{ (void)sizeof(struct _test_no_array_##item *); }
 
 #undef __array
 #define __array(type, item, len)