CONFIG_DEBUG_STACKOVERFLOW hurts

[Eric Sandeen]

Dave Jones wrote:
> On Tue, Sep 11, 2007 at 03:05:52PM -0500, Eric Sandeen wrote:
>  
>  > In light of this, I'd like to propose that we turn off
>  > DEBUG_STACKOVERFLOW in Fedora, at least on x86/4KSTACKS.  I think it
>  > does more harm than good; the warning is going to turn deadly most of
>  > the time.
>  > 
>  > I also had sent a patch to LKML to print whether or not the stack was
>  > overflowing, or had ever overflowed, on a kernel panic.  It's not yet
>  > been merged.
>  > 
>  > ... any comments?  I can file a bug but thought some discussion might be
>  > in order.
> 
> We could turn it off everywhere expect the -debug kernels and
> just have XFS + -debug be a 'dont do that' thing.

Well, I didn't actually *say* xfs ... *cough* ;-)

There have been reports of mount.nfs, for example, using within 600
bytes of the end of the stack... if they'd caught an interrupt at the
end of whatever callchain that was, they'de be uncomfortably close to
the edge too.

And - what is the use of keeping the warning turned on *anywhere* when
really, all it does is turn a near-miss into the real thing?  If you
actually overrun the stack, you're probably going to oops anyway, and
get about the same backtrace - except, hopefully less often, w/o the
warning going off.

I see this almost entirely as statistically shaving another ~500 bytes
off the usable stack, without generating much useful information in return.

Or am I missing some other usefulness of this?

-Eric