Re: hunting an IO hang

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Linus Torvalds's message of 2011-01-17 13:24:55 -0500:
> On Mon, Jan 17, 2011 at 9:40 AM, Chris Mason <chris.mason@oracle.com> wrote:
> >> >
> >> > I've reverted 744ed1442757767ffede5008bb13e0805085902e, and
> >> > d8505dee1a87b8d41b9c4ee1325cd72258226fbc and the run has lasted longer
> >> > than any runs in the past.
> >> >
> >>
> >> Confirmed that reverting these patches makes the problem unreproducible
> >> for the many_dd's + fsmark for at least an hour here.
> >
> > After 2+ hours I'm still running with those two commits gone. A I'm
> > confident they are the cause of the crashes. A I also haven't triggered
> > the cfq stalls without them.
> 
> Ok, so the question is how to proceed from here.
> 
> I can easily revert them, and since I was planning on doing -rc1
> tonight, I probably will. But I promised Chris to delay until tomorrow
> if he needed time to chase this down, and while it's now apparently
> chased down, I'll certainly also be open to delaying until tomorrow if
> somebody has a patch to fix it.
> 
> So right now my plan is:
>  - I will revert those two later today and then release -rc1 in the evening
> UNLESS
>  - somebody posts a patch for the problem in the next few hours and
> Chris/others are willing to give it a good test overnight (or whatever
> people feel is "sufficient" based on how easily they can trigger the
> issue), in which case I'd do -rc1 tomorrow (either with the reverts or
> the patch, depending on how testing works out)

If a patch does come in, I'm happy to test it.  Mel had a test that
triggered within 1-2 minutes, mine took 30 or so, which means I'd want a
2 hour run to convince myself it was really fixed.  But, I'll give Mel's
fs_mark + dd workload a try on the buggy kernel.

-chris

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