Re: pipe/page fault oddness.

From: Dave Jones
Date: Tue Sep 30 2014 - 12:05:33 EST

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


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