Re: [OOPS] 2.6.21-rc6-git5 in cfq_dispatch_insert

[Roland Kuhn]

Hi Jens!

On 24 Apr 2007, at 14:32, Jens Axboe wrote:

> On Tue, Apr 24 2007, Roland Kuhn wrote:
> > Hi Jens!
> >
> > [I made a typo in the Cc: list so that lkml is only included as of
> > now. Actually I copied the typo from you ;-) ]
>
> Well no, you started the typo, I merely propagated it and forgot to  
> fix
> it up :-)
Actually, I copied it from your printk() ;-) (thinking helps...)

> > > > > Sure. You might want to include NFS file access into your tests,
> > > > > since we've not triggered this with locally accessing the disks.
> > > > > BTW:
> > > >
> > > > How are you exporting the directory (what exports options) - how
> > > > is it
> > > > mounted by the client(s)? What chunksize is your raid6 using?
> > >
> > > And what are the nature of the files on the raid (huge, small, ?)  
> > > and
> > > what are the client(s) doing? Just approximately, I know these  
> > > things
> > > can be hard/difficult/impossible to specify.
> > The files are 100-400MB in size and the client is merging them into a
> > new file in the same directory using the ROOT library, which does in
> > essence alternating sequences of
> >
> > _llseek(somewhere)
> > read(n bytes)
> > _llseek(somewhere+n)
> > read(m bytes)
> > ...
> >
> > and then
> >
> > _llseek(somewhere)
> > rt_sigaction(ignore INT)
> > write(n bytes)
> > rt_sigaction(INT->DFL)
> > time()
> > _llseek(somewhere+n)
> > ...
> >
> > where n is of the the order of 30kB. The input files are treated
> > sequentially, not randomly.
>
> Ok, I'll see if I can reproduce it. No luck so far, I'm afraid.
Too bad.

> > BTW: the machine just stopped dead, no sign whatsoever on console or
> > netconsole, so I rebooted with elevator=deadline
> > (need to get some work done besides ;-) )
>
> Unfortunately expected, if we can race and lose an update to - 
> >next_rq,
> we can race and corrupt some of the internal data structures as  
> well. If
> you have the time and inclination, it would be interesting to see  
> if you
> can reproduce with some debugging options enabled:
>
> - Enable all preempt, spinlock and lockdep debugging measures
> - Possibly slab poisoning, although that may slow you down somewhat
Kernel compilation under way, will report back.

> Are you using 4kb stacks?
No idea, 'grep -i stack .config' gives no indication, but ISTR that  
4k was made the default some time back?

Ciao,
                    Roland

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