linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141215055707.GA26225@redhat.com>
Date:	Mon, 15 Dec 2014 00:57:07 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Suresh Siddha <sbsiddha@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Anvin <hpa@...ux.intel.com>
Subject: Re: frequent lockups in 3.18rc4

On Sun, Dec 14, 2014 at 09:47:26PM -0800, Linus Torvalds wrote:

 > so it's always in __do_page_fault, but at sometimes it has gotten into
 > handle_mm_fault too. So it really really looks like it is taking an
 > endless stream of page faults on that "xsaveq" instruction. Presumably
 > the page faulting never actually makes any progress, even though it
 > *thinks* the page tables are fine.
 > 
 > DaveJ - you've seen that "endless page faults" behavior before. You
 > had a few traces that showed it. That was in that whole "pipe/page
 > fault oddness." email thread, where you would get endless faults in
 > copy_page_to_iter() with an error_code=0x2.
 > 
 > That was the one where I chased it down to "page table entry must be
 > marked with _PAGE_PROTNONE", but VM_WRITE in the vma, because your
 > machine was alive enough that you got traces out of the endless loop.

We had a flashback to that old bug last month too.
See this mail & your followup. : https://lkml.org/lkml/2014/11/25/1171
That was during a bisect though, so may have been something
entirely different, but it is a spooky coincidence.

	Dave

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