Re: [BUG] fatal hang untarring 90GB file, possibly writeback related.

[Chris Mason]

Excerpts from James Bottomley's message of 2011-04-27 12:50:00 -0400:
> On Wed, 2011-04-27 at 12:33 -0400, Chris Mason wrote:
> > Probably easier to debug with a sysrq-l and sysrq-w. 
> 
> Yes, just enabling them for the repro ... I didn't echo 1
> > /proc/sys/kernel/sysrq first time around
> 
> >  If you get stuck
> > on the filesystem, it is probably waiting on ram, which it probably
> > can't get because kswapd is spinning.  Eventually everyone backs up
> > waiting for the transaction that never ends.  If we're really lucky it
> > is just GFP_KERNEL where it should NOFS.
> > 
> > Since you're often stuck in different spots inside shrink_slab, we're
> > probably not stuck on a lock.  But, trying with lock debugging, lockdep
> > enabled and preempt on is a good idea to rule out locking mistakes.
> > 
> > Does the fedora debug kernel enable preempt?
> 
> No ... I've taken the Fedora 15 kernel config directly from their
> install CD for this (with a bit of munging to get it to work on -rc4)

Ok, I'd try turning it on so we catch the sleeping with a spinlock held
case better.

-chris
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