linux-kernel - Re: [PATCH] ipmi: Don't allow device module unload when in use

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Date:   Tue, 22 Oct 2019 10:56:29 -0500
From:   Corey Minyard <minyard@....org>
To:     Tony Camuso <tcamuso@...hat.com>
Cc:     openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Corey Minyard <cminyard@...sta.com>
Subject: Re: [PATCH] ipmi: Don't allow device module unload when in use

On Tue, Oct 22, 2019 at 10:29:12AM -0400, Tony Camuso wrote:
> Corey,
> 
> Testing shows that this patch works as expected.

Thanks, I'll add a Tested-by for you.  It's queued for the next merge
window.

-corey

> 
> Regards,
> Tony
> 
> 
> On 10/14/19 11:46 AM, minyard@....org wrote:
> > From: Corey Minyard <cminyard@...sta.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@...hat.com>
> > Signed-off-by: Corey Minyard <cminyard@...sta.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(-)
> > 
> > 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
> > 
>