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

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Message-ID: <20090821190226.GA28519@elte.hu>
Date:	Fri, 21 Aug 2009 21:02:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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()


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 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

Note that's a 32-bit 8K stack oops, so it doesnt apply.

> 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.

This is a 64-bit one, a pty related one and it's not yet clear what 
happened there - but it's certainly possible to overrun any stack.

> > 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.

Agreed. OTOH we have deep callchains in things like execve() too 
which seem to be a lot harder to fix - and those have been around 
for the past ~10 years since i've been looking at max-stacktraces.
I think 4K doesnt cut it anymore.

	Ingo
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