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

From: Michael S. Tsirkin
Date: Sun Jan 10 2016 - 16:40:26 EST

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.