linux-kernel - Re: [PATCH 0/3] [GIT PULL][3.9] tracing: Fixes with flags and latency tracers

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Message-ID: <1363318731.25967.42.camel@gandalf.local.home>
Date:	Thu, 14 Mar 2013 23:38:51 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 0/3] [GIT PULL][3.9] tracing: Fixes with flags and
 latency tracers

On Thu, 2013-03-14 at 17:33 -0400, Steven Rostedt wrote:

> Anyway, here's hopefully my final series of changes for 3.9.
> (Famous last words)

And there's a bug in this patch set. Thanks to Fangguang's auto tests,
it showed a bug in my new work, which points out a bug in this patch
set. The following change is needed to patch 2:

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index eaaccd8..02debab 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2897,7 +2897,9 @@ static void set_tracer_flags(unsigned int mask, int enabled)
 
 	if (mask == TRACE_ITER_OVERWRITE) {
 		ring_buffer_change_overwrite(global_trace.buffer, enabled);
+#ifdef CONFIG_TRACER_MAX_TRACE
 		ring_buffer_change_overwrite(max_tr.buffer, enabled);
+#endif
 	}
 
 	if (mask == TRACE_ITER_PRINTK)


But this bug is worse than the one in my new code. As the new code wont
compile here, this code will, but "max_tr.buffer" will be NULL if
CONFIG_MAX_TRACER_MAX_TRACE is not defined and will cause a NULL pointer
dereference.

I'll update the patch series, test it and push it out again.

Thanks!

-- Steve


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