Re: [PATCH] ioc4: automatically load sgiioc4 subordinate module

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 5 Dec 2008 16:04:37 -0600 (CST)
Brent Casavant <bcasavan@sgi.com> wrote:

> The main ioc4 driver which manages ownership of the SGI IOC4 PCI device
> does not automatically load any of the ioc4 submodules (the sgiioc4 IDE
> and ioc4_serial serial drivers) during PCI device probing.  This causes
> problems when the root device is a DVD-ROM attached to the IOC4 IDE
> interface (e.g. during system installation) as the sgiioc4 module
> will not be loaded and thus the DVD-ROM device will not be available.
> 
> Modify ioc4 to always load the sgiioc4 IDE module if the board carrying
> the IOC4 hardware actually implements the IDE interface (not all boards
> bring this functionality off the IOC4 chip).
> 
> The use of a work procedure is necessary as request_module() cannot be
> called from the device probe path as it eventually calls out to userspace.
> 

This is a fairly common problem, isn't it?  Other drivers handle it via
appropriate udev magic and initrd/initramfs setups.

Is there something special about ioc4 which requires that it have this
magical special handling?

> ---
>  ioc4.c |   26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/misc/ioc4.c b/drivers/misc/ioc4.c
> index 6f76573..36320bd 100644
> --- a/drivers/misc/ioc4.c
> +++ b/drivers/misc/ioc4.c
> @@ -269,6 +269,16 @@ ioc4_variant(struct ioc4_driver_data *idd)
>  	return IOC4_VARIANT_PCI_RT;
>  }
>  
> +static void
> +ioc4_load_modules(struct work_struct *work)
> +{
> +	/* arg just has to be freed */
> +
> +	request_module("sgiioc4");
> +
> +	kfree(work);
> +}
> +
>  /* Adds a new instance of an IOC4 card */
>  static int
>  ioc4_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id)
> @@ -378,6 +388,22 @@ ioc4_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id)
>  	}
>  	mutex_unlock(&ioc4_mutex);
>  
> +	if (idd->idd_variant != IOC4_VARIANT_PCI_RT) {
> +		struct work_struct *work;
> +		work = kzalloc(sizeof(struct work_struct), GFP_KERNEL);
> +		if (!work) {
> +			printk(KERN_WARNING
> +			       "%s: IOC4 unable to allocate memory for "
> +			       "load of sub-modules.\n",
> +			       __FUNCTION__);
> +		}
> +		else {
> +			printk(KERN_INFO "IOC4 loading ioc4 submodule\n");
> +			INIT_WORK(work, ioc4_load_modules);
> +			schedule_work(work);
> +		}
> +	}
> +
>  	return 0;
>  

ioc4 can be compiled as a module.  So if someone does an `rmmod ioc4' after
the schedule_work() and before or during the execution of the work
function, dead machine.

This race is fixable by adding a flush_scheduled_work() into
ioc4_exit(), I expect.