linux-kernel - Re: [BUG] 3.13-rc1 kernel crash when enable all tracepoints

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Date:	Tue, 26 Nov 2013 07:58:59 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jovi Zhangwei <jovi.zhangwei@...il.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] 3.13-rc1 kernel crash when enable all tracepoints

On Tue, 26 Nov 2013 12:38:53 +0800
Jovi Zhangwei <jovi.zhangwei@...il.com> wrote:

> Hi,
> 
> I'm not sure this issue already be fixed or not, it can be reproduced
> permanently.
> 
> (I didn't use git-bisect yet, you guys might can understand it quickly)
> 
> #echo 1 > /sys/kernel/debug/tracing/events/enable
> 
> [  160.472176] BUG: unable to handle kernel NULL pointer dereference
> at           (null)
> [  160.472176] IP: [<ffffffff8132ae40>] strlen+0x0/0x30

I hit this bug last night when testing a fix for another bug. I have a
patch for this too, and will send it out after I put it through my
tests.

You can try it out.

-- Steve

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 52594b2..bdac88c 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -372,7 +372,8 @@ ftrace_define_fields_##call(struct ftrace_event_call *event_call)	\
 	__data_size += (len) * sizeof(type);
 
 #undef __string
-#define __string(item, src) __dynamic_array(char, item, strlen(src) + 1)
+#define __string(item, src) __dynamic_array(char, item,			\
+				    strlen((src) ? (src) : "(null)") + 1)
 
 #undef DECLARE_EVENT_CLASS
 #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
@@ -501,7 +502,7 @@ static inline notrace int ftrace_get_offsets_##call(			\
 
 #undef __assign_str
 #define __assign_str(dst, src)						\
-	strcpy(__get_str(dst), src);
+	strcpy(__get_str(dst), (src) ? (src) : "(null)");
 
 #undef TP_fast_assign
 #define TP_fast_assign(args...) args

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