linux-kernel - Re: pipe/page fault oddness.

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Message-ID: <CA+55aFzTEXxxh_4_BwVydw1UgCu-NRF95OrzVhj=cievXFTJTg@mail.gmail.com>
Date:	Tue, 30 Sep 2014 09:10:26 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Michel Lespinasse <walken@...gle.com>
Subject: Re: pipe/page fault oddness.

On Tue, Sep 30, 2014 at 9:05 AM, Dave Jones <davej@...hat.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
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