linux-kernel - Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c

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Message-ID: <20080828161632.GA13609@cs181140183.pp.htv.fi>
Date:	Thu, 28 Aug 2008 19:16:32 +0300
From:	Adrian Bunk <bunk@...nel.org>
To:	Paul Mundt <lethal@...ux-sh.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Alan D. Brunelle" <Alan.Brunelle@...com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, linux-embedded@...r.kernel.org
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c -
	bisected

On Thu, Aug 28, 2008 at 09:32:13AM +0900, Paul Mundt wrote:
> On Wed, Aug 27, 2008 at 08:35:44PM +0300, Adrian Bunk wrote:
> > On Thu, Aug 28, 2008 at 01:00:52AM +0900, Paul Mundt wrote:
> > > On Wed, Aug 27, 2008 at 02:58:30PM +0300, Adrian Bunk wrote:
> > > In addition to that, debugging the runaway stack users on 4k tends to be
> > > easier anyways since you end up blowing the stack a lot sooner. On sh
> > > we've had pretty good luck with it, though most of our users are using
> > > fairly deterministic workloads and continually profiling the footprint.
> > > Anything that runs away or uses an insane amount of stack space needs to
> > > be fixed well before that anyways, so catching it sooner is always
> > > preferable. I imagine the same case is true for m68knommu (even sans IRQ
> > > stacks).
> > 
> > CONFIG_DEBUG_STACKOVERFLOW should give you the same information, and if
> > wanted with an arbitrary limit.
> > 
> In some cases, yes. In the CONFIG_DEBUG_STACKOVERFLOW case the check is
> only performed from do_IRQ(), which is sporadic at best, especially on
> tickless. While it catches some things, it's not a complete solution in
> and of iteslf.
> 
> In addition to this, there are even fewer platforms that support it than
> there are platforms that do 4k stacks. At first glance, it looks like
> it's only m32r, powerpc, sh, x86, and xtensa.
>...

As far as I can see the only architectures that optionally offer 4kB 
stacks today are m68knommu, s390, sh and x86.

Did I miss some architectures or is 5 < 4 ;) ?

> Others support the Kconfig
> option, but don't seem to realize that it's not an option that the kernel
> does anything with by itself, and so don't actually do anything (ie,
> FRV).

Unless I miss anything these "others" include only FRV.

> > IMHO there seems to currently be a mismatch between it's maintainance 
> > cost and the actual number of users. That's in my opinion the main 
> > problem with it, no matter in which direction it gets resolved.
> > 
> Perhaps that's true on x86, but in general I take issue with that. On sh
> we've had to do very little maintenance for it and most shipping products
> are using it today (at least on MMU-Linux, we don't bother with it on
> nommu). Most of the problems we ran in to with 4k stacks tended to be
> stuff that we wanted to fix for 8k anyways. I suspect that this case is
> true for the other embedded platforms also.
>...

Most stack issues are not platform or architecture specific.

The maintainance effort therefore mostly depends on whether a non-zero 
number of architectures uses 4kB stacks.

And if something is considered to be important for small embedded 
systems, but not supported on ARM, MIPS or PowerPC, then that's 
a bit strange.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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