linux-kernel - Re: [RFC][PATCH V3] axi: add AXI bus driver

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Date:	Mon, 11 Apr 2011 23:36:39 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Greg KH <greg@...ah.com>
Cc:	linux-wireless@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	George Kashperko <george@...u.edu.ua>,
	Arnd Bergmann <arnd@...db.de>,
	Russell King <rmk@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	b43-dev@...ts.infradead.org,
	Michael Büsch <mb@...sch.de>,
	linuxdriverproject <devel@...uxdriverproject.org>,
	Andy Botting <andy@...ybotting.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Larry Finger <Larry.Finger@...inger.net>
Subject: Re: [RFC][PATCH V3] axi: add AXI bus driver

2011/4/11 Greg KH <greg@...ah.com>:
> On Mon, Apr 11, 2011 at 11:19:13PM +0200, Rafał Miłecki wrote:
>> 2011/4/11 Greg KH <greg@...ah.com>:
>> > On Mon, Apr 11, 2011 at 11:25:14PM +0200, Rafał Miłecki wrote:
>> >> +static void axi_release_core_dev(struct device *dev)
>> >> +{
>> >> +     /* Silent lack-of-release warning */
>> >> +}
>> >
>> > Ok, WTF!!!!
>>
>> Thank you for your kindly words. It's much more enjoyable to work on
>> kernel that way. I definitely made that on purpose.
>
> I can't tell if you are kidding or not.

That was 100% irony. I swear I don't enjoy publishing bad code and
getting such a comment.


> Please read the documentation for how to do this properly.  I find it
> really hard to believe that you wrote that comment instead of putting in
> the 2 lines of code required for this function.
>
> Especially as-it-is, your code does not work properly and leaks memory
> badly.  Why would you do that on purpose?

I tried to read some documentation about this.

1) driver-mode/device.txt says only that:
> Callback to free the device after all references have
> gone away. This should be set by the allocator of the
> device (i.e. the bus driver that discovered the device).
I *really* do not know how my driver should "free" core on AXI bus.

2) LDD3 says:
> The method is called when the last reference to the device is removed; it is called
> from the embedded kobject’s release method. All device structures registered with
> the core must have a release method, or the kernel prints out scary complaints.
Well, I do not register any structs for AXI core.

3) Example code from LDD3:
static void ldd_bus_release(struct device *dev)
{
printk(KERN_DEBUG "lddbus release\n");
}
Yeah, that's what I did...

4) SSB in it's ssb_release_dev just calls kfree on struct that was
allocated when registering drivers. *I do not* allocate such a struct,
so I believe I do exactly the same memory leak as SSB does.


Can you spend 2 more minues in addition to commenting my ideas and
help me with writing that 2 lines I missed? Where do I leak memory in
my driver? Which struct should I kfree?

-- 
Rafał
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