linux-kernel - Re: [PATCH 2/2] virtio: don't free memory until the underlying struct device has been released

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Date:	Sun, 4 Jan 2015 17:40:49 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"open list:VIRTIO CORE, NET..." 
	<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 2/2] virtio: don't free memory until the underlying
 struct device has been released

On Sun, Jan 04, 2015 at 10:03:27AM -0500, Sasha Levin wrote:
> On 01/04/2015 06:26 AM, Michael S. Tsirkin wrote:
> > On Fri, Jan 02, 2015 at 02:47:40PM -0500, Sasha Levin wrote:
> >> > When releasing a virtio device, We can't free a struct virtio_device until the
> >> > underlying struct device has been released, which might not happen immediately
> >> > on device_unregister() even if that was the device's last reference.
> >> > 
> >> > Instead, free the memory only once we know the device is gone in the release
> >> > callback.
> >> > 
> >> > Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> > 
> > Isn't this an old bug: do we need to copy stable on a fix?
> > 
> > What is the behaviour without this patch?
> > Is there a way to make this cause a crash?
> 
> It will oops if CONFIG_DEBUG_KOBJECT_RELEASE is enabled. I guess
> it needs to go to stable as well.
> 
> 
> Thanks,
> Sasha

I see.

It's probably a good idea to document the crash in the commit log,
and also add a code comment.

I'll post the series with these minor tweaks, please confirm
that this fixes the issues for you.

-- 
MST
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