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

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Message-ID: <20110411233506.GA13240@kroah.com>
Date:	Mon, 11 Apr 2011 16:35:06 -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 12:45:33AM +0200, Rafał Miłecki wrote:
> 2011/4/12 Greg KH <greg@...ah.com>:
> > 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.
> 
> This is because it is defined as:
> struct axi_device cores[AXI_MAX_NR_CORES];

No way, seriously?

You can't do that, no static struct devices please.  Make these dynamic
and everything will be fine.  The -mm tree used to have a huge warning
if you ever tried to register a statically allocated struct, but that
didn't really work out, but would have saved you a lot of time here,
sorry.

So dynamically allocate the structures and you will be fine.

thanks,

greg k-h
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