linux-kernel - Re: [tip:tracing/urgent] tracing: Fix too large stack usage in do_one

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Message-ID: <alpine.LFD.2.01.0908211108000.3158@localhost.localdomain>
Date:	Fri, 21 Aug 2009 11:13:31 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Ingo Molnar <mingo@...e.hu>, linux-tip-commits@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Dave Jones <davej@...hat.com>,
	Kyle McMartin <kyle@...artin.ca>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	catalin.marinas@....com, a.p.zijlstra@...llo.nl,
	jens.axboe@...cle.com, fweisbec@...il.com, stable@...nel.org,
	srostedt@...hat.com, tglx@...utronix.de
Subject: Re: [tip:tracing/urgent] tracing: Fix too large stack usage in
 do_one_initcall()



On Fri, 21 Aug 2009, Andrew Morton wrote:
> 
> We seem to have overrun an 8k stack in
> http://bugzilla.kernel.org/show_bug.cgi?id=14029

The thread "v2.6.31-rc6: BUG: unable to handle kernel NULL pointer 
dereference at 0000000000000008" also has at least one oops that has 
that "Thread overran stack, or stack corrupted" marker thing.

> Do we have a max-stack-depth tracer widget btw?

Enable FTRACE and then STACK_TRACER. Then just do

	cat /sys/kernel/debug/tracing/stack_trace

and you'll get this.

But if by "widget" you meant something nice and automatic, then I don't 
think so.

> My main concern would be maintenance.  Over time we'll chew more and
> more stack space and eventually we'll get into trouble again.  What
> means do we have for holding the line at 8k, and even improving things?

That's why I think the async thing could fix this - if we _force_ async 
calls to be asynchronous, you won't have the deep callchains for all the 
device discovery thing.

		Linus
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