linux-kernel - Re: [PATCH 2/2] tracing/events: Add kexec tracepoints

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Date:	Tue, 08 Sep 2009 19:02:37 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	rostedt@...dmis.org
Cc:	Li Zefan <lizf@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] tracing/events: Add kexec tracepoints

Steven Rostedt <rostedt@...dmis.org> writes:

> On Tue, 2009-09-08 at 18:27 -0700, Eric W. Biederman wrote:
>> Li Zefan <lizf@...fujitsu.com> writes:
>> 
>> > When panic, save in ring buffer the time when crash happened,
>> > the panic message, etc. And the data can be retrieved from
>> > core dump file using flight-recorder, which is going to be a
>> > module of the crash utility.
>> >
>> > Also if we implement flight-recorder in perf tool, those trace
>> > outputs can be used by perf tool.
>> 
>> Please let's keep dynamic code out of crash_kexec if we can.
>
> What dynamic code? It's a tracepoint not something like the function
> tracer. It is activated via a bit test and a jmp. Not very dynamic.

The philosophy of the crash dump code is that the kernel is broken
trust as little as possible.

Within a few seconds we should be able to get the time from the kernel
that saves the crash dump so I don't see how adding a trace point
adds anything into that code path except an unnecessary dependency
that might have broken.

Or in short you have a full user space to add features to.  Please
don't features to the critical kernel magic that gets you to userspace.

Eric

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