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Subject: Re: [PATCH v2 1/2] xen/xenbus: reference count registered modules
To:     Paul Durrant <pdurrant@amazon.com>
Cc:     xen-devel@lists.xenproject.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Stefano Stabellini <sstabellini@kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>
References: <20191129134306.2738-1-pdurrant@amazon.com>
 <20191129134306.2738-2-pdurrant@amazon.com>
From:   Jan Beulich <jbeulich@suse.com>
Message-ID: <599c254c-035b-33a0-9f32-866ffe644ad5@suse.com>
Date:   Fri, 29 Nov 2019 17:00:58 +0100
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On 29.11.2019 14:43, Paul Durrant wrote:
> To prevent a module being removed whilst attached to a frontend, and

Why only frontend?

> hence xenbus calling into potentially invalid text, take a reference on
> the module before calling the probe() method (dropping it if unsuccessful)
> and drop the reference after returning from the remove() method.
> 
> NOTE: This allows the ad-hoc reference counting in xen-netback to be
>       removed. This will be done in a subsequent patch.
> 
> Suggested-by: Jan Beulich <jbeulich@suse.com>
> Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> 
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -232,9 +232,11 @@ int xenbus_dev_probe(struct device *_dev)
>  		return err;
>  	}
>  
> +	__module_get(drv->driver.owner);

I guess you really want try_module_get() and deal with it returning
false.

Jan