Re: 3.14-rc2 XFS backtrace because irqs_disabled.

Dave Jones
2014-02-12T14:25:55Z

On Wed, Feb 12, 2014 at 05:10:38PM +1100, Dave Chinner wrote:
> On Wed, Feb 12, 2014 at 12:50:27AM -0500, Dave Jones wrote:
> > On Wed, Feb 12, 2014 at 04:40:43PM +1100, Dave Chinner wrote:
> >
> > > None of the XFS code disables interrupts in that path, not does is
> > > call outside XFS except to dispatch IO. The stack is pretty deep at
> > > this point and I know that the standard (non stacked) IO stack can
> > > consume >3kb of stack space when it gets down to having to do memory
> > > reclaim during GFP_NOIO allocation at the lowest level of SCSI
> > > drivers. Stack overruns typically show up with symptoms like we are
> > > seeing.
> > > ..
> > >
> > > Dave, before chasing ghosts, can you (like Eric originally asked)
> > > turn on stack overrun detection?
> >
> > CONFIG_DEBUG_STACKOVERFLOW ? Already turned on.
>
> That only checks stack usage when an interrupt is taken. If no
> interrupts are taken when stack usage is within 128 bytes of
> overflow, then it doesn't catch it.
>
> I tend to use CONFIG_DEBUG_STACK_USAGE=y as it records the maximum
> stack usage of a process via canary overwrites and it records it in
> do_exit().

I had that on too. The only message from it came from quite a while
before the trace that happened overnight..

[ 3415.655125] trinity-c0 (4383) used greatest stack depth: 992 bytes left
[12900.804230] BUG: sleeping function called from invalid context at mm/mempool.c:203

> I also use the stack tracer to record the largest stack
> usage seen so I know exactly what code paths are approaching stack
> overruns...

I can give that a try later.

Dave