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Subject: Re: [PATCH] ipmi: Don't allow device module unload when in use
To:     minyard@acm.org
Cc:     openipmi-developer@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, Corey Minyard <cminyard@mvista.com>
References: <20191014134141.GA25427@t560>
 <20191014154632.11103-1-minyard@acm.org>
From:   Tony Camuso <tcamuso@redhat.com>
Message-ID: <f73aa2ef-e173-db85-e426-3bf380626f66@redhat.com>
Date:   Wed, 16 Oct 2019 15:25:56 -0400
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On 10/14/19 11:46 AM, minyard@acm.org wrote:
> From: Corey Minyard <cminyard@mvista.com>
> 
> If something has the IPMI driver open, don't allow the device
> module to be unloaded.  Before it would unload and the user would
> get errors on use.
> 
> This change is made on user request, and it makes it consistent
> with the I2C driver, which has the same behavior.
> 
> It does change things a little bit with respect to kernel users.
> If the ACPI or IPMI watchdog (or any other kernel user) has
> created a user, then the device module cannot be unloaded.  Before
> it could be unloaded,
> 
> This does not affect hot-plug.  If the device goes away (it's on
> something removable that is removed or is hot-removed via sysfs)
> then it still behaves as it did before.
> 
> Reported-by: tony camuso <tcamuso@redhat.com>
> Signed-off-by: Corey Minyard <cminyard@mvista.com>
> ---
> Tony, here is a suggested change for this.  Can you look it over and
> see if it looks ok?
> 
> Thanks,
> 
> -corey
> 
>   drivers/char/ipmi/ipmi_msghandler.c | 23 ++++++++++++++++-------
>   include/linux/ipmi_smi.h            | 12 ++++++++----
>   2 files changed, 24 insertions(+), 11 deletions(-)

Hi Corey.

You changed ipmi_register_ipmi to ipmi_add_ipmi in ipmi_msghandler, but you
did not change it where it is actually called.

# grep ipmi_register_smi drivers/char/ipmi/*.c
drivers/char/ipmi/ipmi_powernv.c:	rc = ipmi_register_smi(&ipmi_powernv_smi_handlers, ipmi, dev, 0);
drivers/char/ipmi/ipmi_si_intf.c:	rv = ipmi_register_smi(&handlers,
drivers/char/ipmi/ipmi_ssif.c:	rv = ipmi_register_smi(&ssif_info->handlers,

Is there a reason for changing the interface name? Is this something
that I could do instead of troubling you with it?

Regards,
Tony


> 
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index 2aab80e19ae0..15680de18625 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -448,6 +448,8 @@ enum ipmi_stat_indexes {
>   
>   #define IPMI_IPMB_NUM_SEQ	64
>   struct ipmi_smi {
> +	struct module *owner;
> +
>   	/* What interface number are we? */
>   	int intf_num;
>   
> @@ -1220,6 +1222,11 @@ int ipmi_create_user(unsigned int          if_num,
>   	if (rv)
>   		goto out_kfree;
>   
> +	if (!try_module_get(intf->owner)) {
> +		rv = -ENODEV;
> +		goto out_kfree;
> +	}
> +	
>   	/* Note that each existing user holds a refcount to the interface. */
>   	kref_get(&intf->refcount);
>   
> @@ -1349,6 +1356,7 @@ static void _ipmi_destroy_user(struct ipmi_user *user)
>   	}
>   
>   	kref_put(&intf->refcount, intf_free);
> +	module_put(intf->owner);
>   }
>   
>   int ipmi_destroy_user(struct ipmi_user *user)
> @@ -2459,7 +2467,7 @@ static int __get_device_id(struct ipmi_smi *intf, struct bmc_device *bmc)
>    * been recently fetched, this will just use the cached data.  Otherwise
>    * it will run a new fetch.
>    *
> - * Except for the first time this is called (in ipmi_register_smi()),
> + * Except for the first time this is called (in ipmi_add_smi()),
>    * this will always return good data;
>    */
>   static int __bmc_get_device_id(struct ipmi_smi *intf, struct bmc_device *bmc,
> @@ -3377,10 +3385,11 @@ static void redo_bmc_reg(struct work_struct *work)
>   	kref_put(&intf->refcount, intf_free);
>   }
>   
> -int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
> -		      void		       *send_info,
> -		      struct device            *si_dev,
> -		      unsigned char            slave_addr)
> +int ipmi_add_smi(struct module         *owner,
> +		 const struct ipmi_smi_handlers *handlers,
> +		 void		       *send_info,
> +		 struct device         *si_dev,
> +		 unsigned char         slave_addr)
>   {
>   	int              i, j;
>   	int              rv;
> @@ -3406,7 +3415,7 @@ int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
>   		return rv;
>   	}
>   
> -
> +	intf->owner = owner;
>   	intf->bmc = &intf->tmp_bmc;
>   	INIT_LIST_HEAD(&intf->bmc->intfs);
>   	mutex_init(&intf->bmc->dyn_mutex);
> @@ -3514,7 +3523,7 @@ int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
>   
>   	return rv;
>   }
> -EXPORT_SYMBOL(ipmi_register_smi);
> +EXPORT_SYMBOL(ipmi_add_smi);
>   
>   static void deliver_smi_err_response(struct ipmi_smi *intf,
>   				     struct ipmi_smi_msg *msg,
> diff --git a/include/linux/ipmi_smi.h b/include/linux/ipmi_smi.h
> index 4dc66157d872..deec18b8944a 100644
> --- a/include/linux/ipmi_smi.h
> +++ b/include/linux/ipmi_smi.h
> @@ -224,10 +224,14 @@ static inline int ipmi_demangle_device_id(uint8_t netfn, uint8_t cmd,
>    * is called, and the lower layer must get the interface from that
>    * call.
>    */
> -int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
> -		      void                     *send_info,
> -		      struct device            *dev,
> -		      unsigned char            slave_addr);
> +int ipmi_add_smi(struct module            *owner,
> +		 const struct ipmi_smi_handlers *handlers,
> +		 void                     *send_info,
> +		 struct device            *dev,
> +		 unsigned char            slave_addr);
> +
> +#define ipmi_register_smi(handlers, send_info, dev, slave_addr) \
> +	ipmi_add_smi(THIS_MODULE, handlers, send_info, dev, slave_addr)
>   
>   /*
>    * Remove a low-level interface from the IPMI driver.  This will
>