linux-kernel - Re: [PATCH 2/2] virtio_balloon: fix race between migration and ballooning

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Date:	Sun, 10 Jan 2016 23:40:17 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Rafael Aquini <aquini@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] virtio_balloon: fix race between migration and
 ballooning

On Mon, Jan 04, 2016 at 09:27:47AM +0900, Minchan Kim wrote:
> > I think this will cause deadlocks.
> > 
> > pages_lock now nests within page lock, balloon_page_putback
> > nests them in the reverse order.
> 
> In balloon_page_dequeu, we used trylock so I don't think it's
> deadlock.

I went over this again and I don't see the issue anymore.
I think I was mistaken, so I dropped my patch and picked
up yours. Sorry about the noise.


> > 
> > Also, there's another issue there I think: after isolation page could
> > also get freed before we try to lock it.
> 
> If a page was isolated, the page shouldn't stay b_dev_info->pages
> list so balloon_page_dequeue cannot see the page.
> Am I missing something?

I mean without locks, as it is now. With either your or my patch in
place, it's fine.

-- 
MST