linux-kernel - Re: [RFC][BUG] tracer: Fails to work

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Message-ID: <20160128105557.2971f8b9@gandalf.local.home>
Date:	Thu, 28 Jan 2016 10:55:57 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC][BUG] tracer: Fails to work

On Thu, 28 Jan 2016 16:29:57 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Jan 28, 2016 at 02:53:53PM +0000, Mathieu Desnoyers wrote:
> > On x86, many BIOS wipe the memory content even after a warm reset :(
> > The most reliable solution I found on x86 is to use kexec() to
> > boot into a new kernel, mount the DAX filesystem again and read the
> > buffers from there.  
> 
> kexec() is tricky when the kernel is still prefectly fine, I doubt it'll
> work when I've hosed it properly :/

I use it all the time when a kernel crashes. Well, kexec and kdump.
Which by the way, the crash utility has a way to read the ftrace ring
buffer from a kexec kdump core file.

-- Steve