Re: XFS causing stack overflow

Ryan C. England
2011-12-12T13:44:01Z

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Is it possible to apply this patch to my current installation? We use this
box in production and the reboots that we're experiencing are an
inconvenience.

Is there is a walkthrough on how to apply this patch? If not, could your
provide the steps necessary to apply successfully? I would greatly
appreciate it.

Thank you

On Mon, Dec 12, 2011 at 4:00 AM, Dave Chinner <david@fromorbit.com> wrote:

> On Mon, Dec 12, 2011 at 06:13:11AM +0100, Andi Kleen wrote:
> > > It's ~180 bytes, so it's not really that small.
> >
> > Quite small compared to what real code uses. And also fixed
> > size.
> >
> > >
> > > > is on the new stack. ISTs are not used for interrupts, only for
> > > > some special exceptions.
> > >
> > > IST = ???
> >
> > That's a hardware mechanism on x86-64 to switch stacks
> > (Interrupt Stack Table or somesuch)
> >
> > With ISTs it would have been possible to move the the pt_regs too,
> > but the software mechanism is somewhat simpler.
> >
> > > at the top of the stack frame? Is the stack unwinder walking back
> > > across the interrupt stack to the previous task stack?
> >
> > Yes, the unwinder knows about all the extra stacks (interrupt
> > and exception stacks) and crosses them as needed.
> >
> > BTW I suppose it wouldn't be all that hard to add more stacks and
> > switch to them too, similar to what the 32bit do_IRQ does.
> > Perhaps XFS could just allocate its own stack per thread
> > (or maybe only if it detects some specific configuration that
> > is known to need much stack)
>
> That's possible, but rather complex, I think.
> > It would need to be per thread if you could sleep inside them.
>
> Yes, we'd need to sleep, do IO, possibly operate within a
> transaction context, etc, and a workqueue handles all these cases
> without having to do anything special. Splitting the stack at a
> logical point is probably better, such as this patch:
>
> http://oss.sgi.com/archives/xfs/2011-07/msg00443.html
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>

--
Ryan C. England
Corvid Technologies <http://www.corvidtec.com/>
office: 704-799-6944 x158
cell: 980-521-2297

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