linux-kernel - Re: frequent softlockups with 3.10rc6.

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Date:	Tue, 25 Jun 2013 13:29:54 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrey Vagin <avagin@...nvz.org>
Subject: Re: frequent softlockups with 3.10rc6.

On Tue, 2013-06-25 at 13:21 -0400, Steven Rostedt wrote:
> On Tue, 2013-06-25 at 12:55 -0400, Dave Jones wrote:
> 
> > While I've been spinning wheels trying to reproduce that softlockup bug,
> > On another machine I've been refining my list-walk debug patch.
> > I added an ugly "ok, the ringbuffer is playing games with lower two bits" special case.
> > 
> > But what the hell is going on here ?
> > 
> > next->prev should be prev (ffff88023c6cdd18), but was 00ffff88023c6cdd. (next=ffff880243288001).

Ah you didn't handle the bit set case. I just noticed "00" in
00ffff88023c6cdd. To test this, you really need to do a "next & ~3", to
clear the pointer.

Perhaps its best to have just a "raw_list_for_each" that doesn't do any
check, and have the ring buffer use that instead. The
rb_head_page_deactivate() is usually followed by an integrity check
anyway.

-- Steve


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