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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>
 <f73aa2ef-e173-db85-e426-3bf380626f66@redhat.com>
 <20191016193349.GP14232@t560>
From:   Tony Camuso <tcamuso@redhat.com>
Message-ID: <c8660785-c99c-7f5c-25b7-6e37e08aa01f@redhat.com>
Date:   Wed, 16 Oct 2019 15:54:04 -0400
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On 10/16/19 3:33 PM, Corey Minyard wrote:
> On Wed, Oct 16, 2019 at 03:25:56PM -0400, Tony Camuso wrote:
>> 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?
> 
> I don't understand.  You don't say that anything went wrong, you just
> referenced something I changed.
> 
> I changed the name so I could create a macro with that name to pass in
> the module name.  Pretty standard to do in the kernel.  

Can't believe I missed that.

> Is there a
> compile or runtime issue?
> 
> -corey

All is well, so far. Haven't finished testing.

>>
>> 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
>>>
>>