linux-kernel - Re: bad page state in 3.13-rc4

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Date:	Thu, 19 Dec 2013 20:00:42 -0500
From:	Dave Jones <davej@...hat.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kent Overstreet <kmo@...erainc.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Christoph Lameter <cl@...two.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: bad page state in 3.13-rc4

On Thu, Dec 19, 2013 at 06:38:54PM -0500, Benjamin LaHaise wrote:
 > On Thu, Dec 19, 2013 at 03:24:16PM -0500, Dave Jones wrote:
 > > Yes. Note the original trace in this thread was a VM_BUG_ON(atomic_read(&page->_count) <= 0);
 > > 
 > > Right after these crashes btw, the box locks up solid. So bad that traces don't
 > > always make it over usb-serial. Annoying.
 > 
 > I think I finally have an idea what's going on now.  Kent's changes in 
 > e34ecee2ae791df674dfb466ce40692ca6218e43 are broken and result in a memory 
 > leak of the aio kioctx.  This eventually leads to the system running out of 
 > memory, which ends up triggering the otherwise hard to hit error paths in 
 > aio_setup_ring().  Linus' suggested changes should fix the badness in the 
 > aio_setup_ring(), but more work has to be done to fix up the percpu 
 > reference counting tie in with the aio code.  I'll fix this up in the 
 > morning if nobody beats me to it over night, as I'm just heading out right 
 > now.

That would explain why I'm having difficulty repeating it in a hurry if it
takes hours of runtime for the leak to reach a point where it becomes a problem.

	Dave

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