linux-kernel - Re: [PATCH v3 1/3] tracing: Show real address for trace event arguments

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Date:   Mon, 19 Apr 2021 14:22:29 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] tracing: Show real address for trace event
 arguments

On Mon, 19 Apr 2021 14:08:14 +0100
Jon Hunter <jonathanh@...dia.com> wrote:

> I have encountered the following crash on a couple of our ARM64 Jetson
> platforms and bisect is pointing to this change. The crash I am seeing
> is on boot when I am directing the trace prints to the console by adding
> 'tp_printk trace_event="cpu_frequency,cpu_frequency_limits"' to the
> kernel command line and enabling CONFIG_BOOTTIME_TRACING. Reverting this
> change does fix the problem. Let me know if you have any thoughts.

Thanks for the report. I was able to reproduce this on x86 as well.

It's the tp_printk that's the problem. Does this fix it for you?

-- Steve

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 66a4ad93b5e9..f1ce4be7a499 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3580,7 +3580,11 @@ static char *trace_iter_expand_format(struct trace_iterator *iter)
 {
 	char *tmp;
 
-	if (iter->fmt == static_fmt_buf)
+	/*
+	 * iter->tr is NULL when used with tp_printk, which makes
+	 * this get called where it is not safe to call krealloc().
+	 */
+	if (!iter->tr || iter->fmt == static_fmt_buf)
 		return NULL;
 
 	tmp = krealloc(iter->fmt, iter->fmt_size + STATIC_FMT_BUF_SIZE,
@@ -3799,7 +3803,7 @@ const char *trace_event_format(struct trace_iterator *iter, const char *fmt)
 	if (WARN_ON_ONCE(!fmt))
 		return fmt;
 
-	if (iter->tr->trace_flags & TRACE_ITER_HASH_PTR)
+	if (!iter->tr || iter->tr->trace_flags & TRACE_ITER_HASH_PTR)
 		return fmt;
 
 	p = fmt;
@@ -9931,7 +9935,7 @@ void __init early_trace_init(void)
 {
 	if (tracepoint_printk) {
 		tracepoint_print_iter =
-			kmalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
+			kzalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
 		if (MEM_FAIL(!tracepoint_print_iter,
 			     "Failed to allocate trace iterator\n"))
 			tracepoint_printk = 0;