Re: [PATCH] 9p/xen: mark 9p transport device as closing when removing it

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Mon, Dec 08, 2025 at 11:51:55AM -0800, Ariadne Conill wrote:
> We need to do this so that we can signal to the other end that the
> device is being removed, so that it will release its claim on the
> underlying memory allocation.  Otherwise releasing the grant-table
> entries is deferred resulting in a kernel oops since the pages have
> already been freed.
> 
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Fixes: 71ebd71921e45 ("xen/9pfs: connect to the backend")
> Signed-off-by: Ariadne Conill <ariadne@ariadne.space>
> Signed-off-by: Alex Zenla <alex@xxxxxxxxx>
> ---
>  net/9p/trans_xen.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
> index b9ff69c7522a..cde283c42dc6 100644
> --- a/net/9p/trans_xen.c
> +++ b/net/9p/trans_xen.c
> @@ -312,6 +312,7 @@ static void xen_9pfs_front_remove(struct xenbus_device 
> *dev)
>  {
>       struct xen_9pfs_front_priv *priv = dev_get_drvdata(&dev->dev);
>  
> +     xenbus_switch_state(dev, XenbusStateClosing);

I think you need to wait for the backend to acknowledge it by switching
its state, before continuing. See for example
xennet_remove()->xennet_bus_close() in drivers/net/xen-netfront.c.

>       dev_set_drvdata(&dev->dev, NULL);
>       xen_9pfs_front_free(priv);
>  }
> -- 
> 2.52.0
> 
> 

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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