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

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Message-ID: <20140930160510.GA15903@redhat.com>
Date:	Tue, 30 Sep 2014 12:05:10 -0400
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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 08:52:08AM -0700, Linus Torvalds wrote:

 > So if it's looping on that fault, what seems to happen is that the
 > page fault keeps happening.
 > 
 > Can you recreate this? Because if you can, please try to revert commit
 > e4a1cc56e4d7 ("x86: mm: drop TLB flush from ptep_set_access_flags").
 > Maybe the TLB has it read-only, and it doesn't get flushed, and the
 > page fault happens over and over again.

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.

If I can reproduce it, I'll then try that revert.

 > What kind of CPU is the problematic machine? There was some question
 > about just how architectural the whole "TLB entry causing a page fault
 > gets invalidated automatically" really is.

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

	Dave

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