Re: 2.6.19-rc6 : Spontaneous reboots, stack overflows - seems to implicate xfs, scsi, networking, SMP

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On 24/11/06, David Chinner <[email protected]> wrote:
On Thu, Nov 23, 2006 at 07:37:00PM +0100, Arjan van de Ven wrote:
> On Thu, 2006-11-23 at 14:16 +0100, Ingo Oeser wrote:
> > Hi there,
> >
> > David Chinner schrieb:
> > > If the softirqs were run on a different stack, then a lot of these
>
> softirqs DO run on their own stack!

So they run on a separate stack for 4k stacks on x86?

Yes, with 4K stacks there's sepperate IRQ stack.

From the help text for CONFIG_4KSTACKS :
"If you say Y here the kernel will use a 4Kb stacksize for the
kernel stack attached to each process/thread. This facilitates
running more threads on a system and also reduces the pressure
on the VM subsystem for higher order allocations. This option
will also use IRQ stacks to compensate for the reduced stackspace."


They don't run on a separate stack for 8k stacks on x86 -
Jesper's traces show that - so this may indicate an issue
with the methodology used to generate the stack overflow
traces inteh first place. i.e. if 4k stacks use a separate
stack, then most of the reported overflows are spurious
and would not normally occur on 4k stack systems..

Well, some of the traces show that we were down to ~3K stack free with
8K stacks, so ~5K used. Even with 4K stacks and sepperate stack for
IRQs we will still be uncomfortably close to the edge in those cases.
Also, I did manage to capture a single line via netconsole while
running with 4K stacks :
   do_IRQ: stack overflow: 492
Unfortunately that was the only line that made it to the remote log
server, so I don't have the actual trace for that one. But it does
show that there really is an issue when running with 4K stacks, IRQ
stacks or no.


--
Jesper Juhl <[email protected]>
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