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Message-ID: <1372181394.18733.222.camel@gandalf.local.home>
Subject: Re: frequent softlockups with 3.10rc6.
From: Steven Rostedt <rostedt@goodmis.org>
To: Dave Jones <davej@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrey Vagin <avagin@openvz.org>
Date: Tue, 25 Jun 2013 13:29:54 -0400
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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