linux-kernel - Re: mm: BUG in unmap_page

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Date:	Wed, 10 Sep 2014 12:09:40 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Cyrill Gorcunov <gorcunov@...il.com>
Subject: Re: mm: BUG in unmap_page_range

On Wed, 10 Sep 2014, Sasha Levin wrote:
> On 09/09/2014 10:45 PM, Hugh Dickins wrote:
> > Sasha, you say you're getting plenty of these now, but I've only seen
> > the dump for one of them, on Aug26: please post a few more dumps, so
> > that we can look for commonality.
> 
> I wasn't saving older logs for this issue so I only have 2 traces from
> tonight. If that's not enough please let me know and I'll try to add
> a few more.

Thanks, these two are useful, mainly because the register contents most
likely to be ptes are in both of these ...900, with no sign of a ...902.

So the RW bit I got excited about yesterday is clearly not necessary for
the bug (though it's still possible that it was good for implicating page
migration, and page migration still play a part in the story).

> > And please attach a disassembly of change_protection_range() (noting
> > which of the dumps it corresponds to, in case it has changed around):
> > "Code" just shows a cluster of ud2s for the unlikely bugs at end of the
> > function, we cannot tell at all what should be in the registers by then.
> 
> change_protection_range() got inlined into change_protection(), it applies to
> both traces above:

Thanks for supplying, but the change in inlining means that
change_protection_range() and change_protection() are no longer
relevant for these traces, we now need to see change_pte_range()
instead, to confirm that what I expect are ptes are indeed ptes.

If you can include line numbers (objdump -ld) in the disassembly, so
much the better, but should be decipherable without.  (Or objdump -Sd
for source, but I often find that harder to unscramble, can't say why.)

Thanks,
Hugh
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