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Date:   Tue, 15 Sep 2020 12:24:52 -0700
From:   Linus Torvalds <>
To:     Matthieu Baerts <>
Cc:     Michael Larabel <>,
        Matthew Wilcox <>,
        Amir Goldstein <>,
        "Ted Ts'o" <>,
        Andreas Dilger <>,
        Ext4 Developers List <>,
        Jan Kara <>,
        linux-fsdevel <>
Subject: Re: Kernel Benchmarking

On Tue, Sep 15, 2020 at 12:01 PM Matthieu Baerts
<> wrote:
> Earlier today, I got one trace with 'sysrq-T' but it is more than 1100
> lines. It is attached to this email also with a version from
> "", I hope that's alright.

Yeah, there's nothing interesting there.

The only relevant tasks seem to be the packetdrill ones that are
blocked on the page lock. I don't see anything that looks even
*remotely* like it could be holding a page lock and be waiting for
anything else.

A couple of pipe readers, a number of parents waiting on their
children, one futex waiter, one select loop.. Nothing at all
unexpected or remotely suspicious.

The packetdrill ones look very similar.

> I forgot one important thing, I was on top of David Miller's net-next
> branch by reflex. I can redo the traces on top of linux-next if needed.

Not likely an issue.

I'll go stare at the page lock code again to see if I've missed
anything. I still suspect it's a latent ABBA deadlock that is just
much *much* easier to trigger with the synchronous lock handoff, but I
don't see where it is.

I guess this is all fairly theoretical since we apparently need to do
that hybrid "limited fairness" patch anyway, and it fixes your issue,
but I hate not understanding the problem.


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