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

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Message-ID: <20110411223632.GB31833@kroah.com>
Date:	Mon, 11 Apr 2011 15:36:32 -0700
From:	Greg KH <greg@...ah.com>
To:	Rafał Miłecki <zajec5@...il.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

On Tue, Apr 12, 2011 at 12:12:47AM +0200, Rafał Miłecki wrote:
> 2011/4/11 Greg KH <greg@...ah.com>:
> > On Mon, Apr 11, 2011 at 11:36:39PM +0200, Rafał Miłecki wrote:
> >> 2011/4/11 Greg KH <greg@...ah.com>:
> >> > 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.
> >
> > The structure that you have created, added to the bus, is now ready to
> > have its memory freed.  So free it.
> >
> > This usually means something like:
> >        struct my_obj = to_my_obj(dev);
> >        kfree(my_obj);
> > in the release function.
> 
> I register core->dev to the bus (I set core->dev.bus and
> core->dev.parent, is that what you mean?). This core->dev is "struct
> dev" embedded in "struct axi_device". By embedded I mean it is *not* a
> pointer, I do not alloc it, it's part of the "struct axi_device".

That is exactly as it should be.

Then in your release function, free the struct axi_device.  It's that
simple.  To try to free it before then would be wrong and cause
problems.

> >> 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.
> >
> > Yes you did, otherwise you would have never seen that callback warning
> > you that you needed a release function.
> 
> I was thinking about alloc, sorry, ignore this one.
> 
> 
> >> 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.
> >
> > Well someone allocated it, right?  Who did it?  If it wasn't you, where
> > did that structure come from and why are you registering it on your bus?
> >
> >> 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?
> >
> > The structure that you wrap around 'struct device' for your bus.
> 
> As explained above, this I do not dynamically alloc this 'struct
> device'. So is there really any memory leak?

Yes, no one ever freed your struct axi_device that you created.

thanks,

greg k-h
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