Re: oops with dual xeon 2.8ghz 4gb ram +smp, software raid, lvm, and xfs

[Jens Axboe <axboe@suse.de>]

On Wed, Nov 24 2004, Andrew Morton wrote:
> Jens Axboe <axboe@suse.de> wrote:
> >
> > On Thu, Nov 25 2004, Neil Brown wrote:
> > > On Wednesday November 24, akpm@osdl.org wrote:
> > > > Neil Brown <neilb@cse.unsw.edu.au> wrote:
> > > > >
> > > > > Would the following (untested-but-seems-to-compile -
> > > > > explanation-of-concept) patch be at all reasonable to avoid stack
> > > > > depth problems with stacked block devices, or is adding stuff to
> > > > > task_struct frowned upon? 
> > > > 
> > > > It's always a tradeoff - we've put things in task_struct before to get
> > > > around sticky situations.  Certainly, removing potentially unbounded stack
> > > > utilisation is a worthwhile thing to do.
> > > > 
> > > > The patch bends my brain a bit.
> > > 
> > > Recursion is like that (... like recursion, that is :-).
> > 
> > Pardon my ignorance, but where is the bug that called for something like
> > this?
> 
> Well there was an xfs-on-raid-on-lvm stack overrun reported, but the
> general problem we're addressing here is that stacking drivers can cause
> arbitrary amounts of kernel stack windup.

Ok. Without b[] on the stack locally, I don't think it's an issue.

> > I can't say I love the idea of adding a bio list structure to the
> > tasklist, it feels pretty hacky. generic_make_request() doesn't really
> > use that much stack, if you just kill the BDEVNAME_SIZE struct.
> 
> Looks like a sensible thing to do, although it would be tidier to move the
> whole thing into a separate function, no?

Yep, works for me.

-- 
Jens Axboe