linux-kernel - Re: dma-debug: add a check dma memory leaks

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Date:	Tue, 21 Apr 2009 11:20:16 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	David Woodhouse <dwmw2@...radead.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	reinette.chatre@...el.com, benh@...nel.crashing.org, greg@...ah.com
Subject: Re: dma-debug: add a check dma memory leaks

On Fri, Apr 17, 2009 at 10:51:05PM +0100, David Woodhouse wrote:
> On Mon, 2009-03-30 at 21:01 +0000, Linux Kernel Mailing List wrote:
> > Gitweb:     http://git.kernel.org/linus/41531c8f5f05aba5ec645d9770557eedbf75b422
> > Commit:     41531c8f5f05aba5ec645d9770557eedbf75b422
> 
> >     dma-debug: add a check dma memory leaks
> >     
> >     Impact: allow architectures to monitor busses for dma mem leakage
> >     
> >     This patch adds checking code to detect if a device has pending DMA
> >     operations when it is about to be unbound from its device driver.
> >     
> >     Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> 
> 
> > +static int dma_debug_device_change(struct notifier_block *nb,
> > +				    unsigned long action, void *data)
> > +{
> > +	struct device *dev = data;
> > +	int count;
> > +
> > +
> > +	switch (action) {
> > +	case BUS_NOTIFY_UNBIND_DRIVER:
> > +		count = device_dma_allocations(dev);
> > +		if (count == 0)
> > +			break;
> > +		err_printk(dev, NULL, "DMA-API: device driver has pending "
> > +				"DMA allocations while released from device "
> > +				"[count=%d]\n", count);
> 
> Hm, cute... but not quite functioning as you intended. If you look at
> __device_release_driver() in drivers/base/dd.c you'll see it actually
> calls the notifier _before_ calling into the driver's ->remove() method.
> So it's hardly surprising that not everything has been freed yet...
> 
> Reported by Reinette when it bit iwlwifi.
> 
> Ben, can we get away with changing the order so that the ->remove() is
> called before the notifier, in this case?

Ben? I would like to keep this check. If its not possible to move this
one behind the drivers ->remove function it may be an option to add
another notifier?

Joerg

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