Re: x86: 4kstacks default

From: Andrew Morton
Date: Sat Apr 19 2008 - 13:49:29 EST


> On Sat, 19 Apr 2008 16:23:29 +0200 Ingo Molnar <mingo@xxxxxxx> wrote:
>
> * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> > > config 4KSTACKS
> > > bool "Use 4Kb for kernel stacks instead of 8Kb"
> > > - depends on DEBUG_KERNEL
> > > depends on X86_32
> > > + default y
> >
> > This patch will cause kernels to crash.
>
> what mainline kernels crash and how will they crash?

There has been a dribble of reports - I don't have the links handy, nor did
I search for them.

> Fedora and other
> distros have had 4K stacks enabled for years:
>
> $ grep 4K /boot/config-2.6.24-9.fc9
> CONFIG_4KSTACKS=y
>
> and we've conducted tens of thousands of bootup tests with all sorts of
> drivers and kernel options enabled and have yet to see a single crash
> due to 4K stacks.

I doubt if you're testing things like nfsd-on-xfs-on-md-on-porky-scsi-driver.

Enable CONFIG_DEBUG_STACK_USAGE. Monitor the results. It's so scary that
I wonder if the feature is busted.

> So basically the kernel default just follows the
> common distro default now. (distros and users can still disable it)

Apparently not. I wouldn't enable it if I had a distro.

Anyway. We should be having this sort of discussion _before_ a patch
gets merged, no?
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