Re: [PATCH] fsl-edma: tracing: no ptr dereference during log output

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 30 Jun 2026 16:05:44 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> >  	TP_printk("offset %08x: value %08x",
> > -		(u32)(__entry->addr - __entry->edma->membase), __entry->value)
> > +		(u32)(__entry->addr - __entry->membase), __entry->value)  
> 
> Hmm, I think I should update the TP_printk checks at boot to cover this too.

I created the following to catch this:

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index c46e623e7e0d..2da3c02bea54 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -400,10 +400,37 @@ static bool process_string(const char *fmt, int len, struct trace_event_call *ca
 	return true;
 }
 
+static void test_double_dereference(const char *str, int len,
+				    struct trace_event_call *call)
+{
+	const char *ptr;
+	const char *end = str + len;
+
+	ptr = strstr(str, "REC->");
+
+	while (ptr && ptr < end) {
+
+		ptr += 5;
+		for (; ptr < end; ptr++) {
+			if (ptr[0] == '-' && ptr[1] == '>') {
+				WARN_ONCE(1, "Event %s has double dereference in TP_printk: %*s\n",
+					  trace_event_name(call), len, str);
+				return;
+			}
+			if (!isalnum(*ptr) && *ptr != '_')
+				break;
+		}
+
+		ptr = strstr(ptr, "REC->");
+	}
+}
+
 static void handle_dereference_arg(const char *arg_str, u64 string_flags, int len,
 				   u64 *dereference_flags, int arg,
 				   struct trace_event_call *call)
 {
+	test_double_dereference(arg_str, len, call);
+
 	if (string_flags & (1ULL << arg)) {
 		if (process_string(arg_str, len, call))
 			*dereference_flags &= ~(1ULL << arg);

Enabled this event to see if it would trigger, but instead it found *another* BUG!

[    0.719012][    T0] ------------[ cut here ]------------
[    0.720850][    T0] Event ufshcd_exception_event has double dereference in TP_printk: dev_name(REC->hba->dev), REC->status
[    0.724646][    T0] WARNING: kernel/trace/trace_events.c:416 at handle_dereference_arg+0x342/0x5a0, CPU#0: swapper/0/0


I'll go make a fix for the ufshcd_exception_event event, and then I will
definitely add this patch to make sure this bug isn't in other places.

-- Steve