Messages in this thread | | | Subject | Re: [PATCH] powerpc/powernv/npu: Fix reference leak | From | Alexey Kardashevskiy <> | Date | Mon, 29 Apr 2019 16:01:29 +1000 |
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On 20/04/2019 01:34, Greg Kurz wrote: > Since 902bdc57451c, get_pci_dev() calls pci_get_domain_bus_and_slot(). This > has the effect of incrementing the reference count of the PCI device, as > explained in drivers/pci/search.c: > > * Given a PCI domain, bus, and slot/function number, the desired PCI > * device is located in the list of PCI devices. If the device is > * found, its reference count is increased and this function returns a > * pointer to its data structure. The caller must decrement the > * reference count by calling pci_dev_put(). If no device is found, > * %NULL is returned. > > Nothing was done to call pci_dev_put() and the reference count of GPU and > NPU PCI devices rockets up. > > A natural way to fix this would be to teach the callers about the change, > so that they call pci_dev_put() when done with the pointer. This turns > out to be quite intrusive, as it affects many paths in npu-dma.c, > pci-ioda.c and vfio_pci_nvlink2.c.
afaict this referencing is only done to protect the current traverser and what you've done is actually a natural way (and the generic pci_get_dev_by_id() does exactly the same), although this looks a bit weird.
> Also, the issue appeared in 4.16 and > some affected code got moved around since then: it would be problematic > to backport the fix to stable releases. > > All that code never cared for reference counting anyway. Call pci_dev_put() > from get_pci_dev() to revert to the previous behavior. >> Fixes: 902bdc57451c ("powerpc/powernv/idoa: Remove unnecessary pcidev from pci_dn") > Cc: stable@vger.kernel.org # v4.16 > Signed-off-by: Greg Kurz <groug@kaod.org> > --- > arch/powerpc/platforms/powernv/npu-dma.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c > index e713ade30087..d8f3647e8fb2 100644 > --- a/arch/powerpc/platforms/powernv/npu-dma.c > +++ b/arch/powerpc/platforms/powernv/npu-dma.c > @@ -31,9 +31,22 @@ static DEFINE_SPINLOCK(npu_context_lock); > static struct pci_dev *get_pci_dev(struct device_node *dn) > { > struct pci_dn *pdn = PCI_DN(dn); > + struct pci_dev *pdev; > > - return pci_get_domain_bus_and_slot(pci_domain_nr(pdn->phb->bus), > + pdev = pci_get_domain_bus_and_slot(pci_domain_nr(pdn->phb->bus), > pdn->busno, pdn->devfn); > + > + /* > + * pci_get_domain_bus_and_slot() increased the reference count of > + * the PCI device, but callers don't need that actually as the PE > + * already holds a reference to the device.
Imho this would be just enough.
Anyway,
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
How did you find it? :)
> Since callers aren't > + * aware of the reference count change, call pci_dev_put() now to > + * avoid leaks. > + */ > + if (pdev) > + pci_dev_put(pdev); > + > + return pdev; > } > > /* Given a NPU device get the associated PCI device. */ >
-- Alexey
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