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Date: Tue, 30 Sep 2014 09:10:26 -0700
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Subject: Re: pipe/page fault oddness.
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dave Jones <davej@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Michel Lespinasse <walken@google.com>
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On Tue, Sep 30, 2014 at 9:05 AM, Dave Jones <davej@redhat.com> wrote:
>
> I left it spinning overnight in case someone wanted me to probe it
> further, so I haven't tried reproducing it yet.  It took ~12 hours
> yesterday before it got in that state.  I'll restart it, and tell it
> to only use pipe fd's, which might speed things up a little.

Actually, if you haven't restarted it yet, do a few more "Sysrq-T"'s
to see if the stack below the page fault ever changes. Is it *always*
that "second access by fault_in_pages_writeable()" or migth there be
some looping going on in copy_page_to_iter() after all? (Quite
frankly, I don't see how such looping could happen with a good
compiler, and 4.8.3 should be good, but just in case).

It's an unlikely scenario, so if you already rebooted, not a big deal.

> model name      : Intel(R) Core(TM) i5-4670T CPU @ 2.30GHz

Ok, that pretty much throws the "maybe AMD did something different"
theory out of the water. Something subtler. Still worth trying the
revert.

            Linus