CONFIG_DEBUG_STACKOVERFLOW hurts

[Dave Jones]

On Tue, Sep 11, 2007 at 04:05:09PM -0500, Eric Sandeen wrote:
 > 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?

Hmm, good point.

	Dave

-- 
http://www.codemonkey.org.uk