Re: refcount leak in pci_get_device()?

[Alex Chiang]

* Greg KH <gregkh@xxxxxxx>:
> On Thu, Aug 21, 2008 at 02:25:04PM -0600, Matthew Wilcox wrote:
> > On Thu, Aug 21, 2008 at 02:19:18PM -0600, Alex Chiang wrote:
> > > #define for_each_pci_dev(d) while ((d = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, d)) != NULL)
> > > 
> > > That eventually calls pci_get_dev_by_id(), which increases the
> > > refcount on the device, but never decrements it.
> > > 
> > > Looks like that change in behavior happened here:
> > > 
> > > 	PCI: clean up search.c a lot
> > > 	95247b57ed844511a212265b45cf9a919753aea1
> > > 
> > > pci_get_device() used to decrement the refcount, but no longer
> > > does.
> > > 
> > > Thanks to Matthew Wilcox for helping me get this far...
> > > 
> > > Like I said, I'm still trying to track down my particular issue,
> > > but I'd like to get your opinion on this.
> > 
> > In particular, I'd like to know whether this should be fixed by
> > pci_get_dev_by_id() decrementing the refcount of from/dev_start,
> > pci_get_subsys() decrementing 'from', or by bus_find_device()
> > decrementing 'start'.  It looks like bus_find_device() is the place
> > where this should logically happen, but the kerneldoc doesn't document
> > the intended behaviour.
> 
> Ah, no the driver core isn't supposed to do this, it's something the pci
> functions do out of "niceness" as that's how we can use them in an
> iterator properly.
> 
> Does the following (untested) patch fix the issue for you all?

Perfect, yes.

I applied it, and observed the refcount on the device I was using
to debug this problem.

I was able to modprobe acpiphp successfully, and echo 0 into the
device's 'power' file.

I then watched the rest of the hotplug core do its thing,
decrementing the refcount properly along the way, and at the end,
we did call pci_release_dev(), as I originally expected to. :)

Just to verify, I toggled the device's power a few times (echoing
a 1 and then a 0, etc.) and watched the refcounts. After each
offline, we properly called pci_release_dev().

Thanks for fixing this. It fixes a pretty bad leak in the hotplug
core (we were leaking an entire struct pci_dev * # of functions
for each offlined card, the first time around; subsequent
onlines/offlines were ok).

Tested-by: Alex Chiang <achiang@xxxxxx>

/ac

> 
> thanks,
> 
> greg k-h
> 
> --------------
> Subject: PCI: fix reference leak in pci_get_dev_by_id()
> 
> From: Greg Kroah-Hartman <gregkh@xxxxxxx>
> 
> Alex Chiang and Matthew Wilcox pointed out that pci_get_dev_by_id() does
> not properly decrement the reference on the from pointer if it is
> present, like the documentation for the function states it will.
> 
> Cc: Matthew Wilcox <matthew@xxxxxx>
> Cc: Alex Chiang <achiang@xxxxxx>
> Cc: stable <stable@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
> 
> 
> diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> index 217814f..3b3b5f1 100644
> --- a/drivers/pci/search.c
> +++ b/drivers/pci/search.c
> @@ -280,6 +280,8 @@ static struct pci_dev *pci_get_dev_by_id(const struct pci_device_id *id,
>  			      match_pci_dev_by_id);
>  	if (dev)
>  		pdev = to_pci_dev(dev);
> +	if (from)
> +		pci_dev_put(from);
>  	return pdev;
>  }
>  
> 
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