linux-kernel - Re: [PATCH 5.4] xen-netback: move removal of "hotplug-status" to the right place

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Message-ID: <Y6CGaHI554sbb9zt@kroah.com>
Date:   Mon, 19 Dec 2022 16:42:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pratyush Yadav <ptyadav@...zon.de>
Cc:     stable@...r.kernel.org, Wei Liu <wei.liu@...nel.org>,
        Paul Durrant <paul@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>,
        Puranjay Mohan <pjy@...zon.de>,
        Maximilian Heyne <mheyne@...zon.de>,
        Julien Grall <julien@....org>, xen-devel@...ts.xenproject.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5.4] xen-netback: move removal of "hotplug-status" to the
 right place

On Mon, Dec 19, 2022 at 04:37:10PM +0100, Pratyush Yadav wrote:
> The removal of "hotplug-status" has moved around a bit. First it was
> moved from netback_remove() to hotplug_status_changed() in upstream
> commit 1f2565780e9b ("xen-netback: remove 'hotplug-status' once it has
> served its purpose"). Then the change was reverted in upstream commit
> 0f4558ae9187 ("Revert "xen-netback: remove 'hotplug-status' once it has
> served its purpose""), but it moved the removal to backend_disconnect().
> Then the upstream commit c55f34b6aec2 ("xen-netback: only remove
> 'hotplug-status' when the vif is actually destroyed") moved it finally
> back to netback_remove(). The thing to note being it is removed
> unconditionally this time around.
> 
> The story on v5.4.y adds to this confusion. Commit 60e4e3198ce8 ("Revert
> "xen-netback: remove 'hotplug-status' once it has served its purpose"")
> is backported to v5.4.y but the original commit that it tries to revert
> was never present on 5.4. So the backport incorrectly ends up just
> adding another xenbus_rm() of "hotplug-status" in backend_disconnect().
> 
> Now in v5.4.y it is removed in both backend_disconnect() and
> netback_remove(). But it should only be removed in netback_remove(), as
> the upstream version does.
> 
> Removing "hotplug-status" in backend_disconnect() causes problems when
> the frontend unilaterally disconnects, as explained in
> c55f34b6aec2 ("xen-netback: only remove 'hotplug-status' when the vif is
> actually destroyed").
> 
> Remove "hotplug-status" in the same place as it is done on the upstream
> version to ensure unilateral re-connection of frontend continues to
> work.
> 
> Fixes: 60e4e3198ce8 ("Revert "xen-netback: remove 'hotplug-status' once it has served its purpose"")
> Signed-off-by: Pratyush Yadav <ptyadav@...zon.de>
> ---
>  drivers/net/xen-netback/xenbus.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Now queued up, thanks.

greg k-h