Re: [dpdk-dev] [RFC V1] examples/l3fwd-power: fix memory leak for rte_pci_device

[Thomas Monjalon <thomas@monjalon.net>]

17/09/2021 04:13, Huisong Li:
> 在 2021/9/16 18:36, Thomas Monjalon 写道:
> > 16/09/2021 10:01, Huisong Li:
> >> 在 2021/9/8 15:20, Thomas Monjalon 写道:
> >>> 08/09/2021 04:01, Huisong Li:
> >>>> 在 2021/9/7 16:53, Thomas Monjalon 写道:
> >>>>> 07/09/2021 05:41, Huisong Li:
> >>>>>> Calling rte_eth_dev_close() will release resources of eth device and close
> >>>>>> it. But rte_pci_device struct isn't released when app exit, which will lead
> >>>>>> to memory leak.
> >>>>> That's a PMD issue.
> >>>>> When the last port of a PCI device is closed, the device should be freed.
> >>>> Why is this a PMD problem? I don't understand.
> >>> In the PMD close function, freeing of PCI device must be managed,
> >>> so the app doesn't have to bother.
> >> I know what you mean. Currently, there are two ways to close PMD device
> >> (rte_eth_dev_close() and rte_dev_remove()).
> >>
> >> For rte_dev_remove(), eth device can be closed and rte_pci_device also
> >> can be freed, so it can make app not care about that.
> >>
> >> But dev_close() is only used to close eth device, and nothing about
> >> rte_pci_device is involved in the framework layer
> >>
> >> call stack of dev_close(). The rte_pci_device is allocated and
> >> initialized when the rte_pci_bus scans "/sys/bus/pci/devices" directory.
> >>
> >> Generally, the PMD of eth devices operates on the basis of eth devices,
> >> and rarely on rte_pci_device.
> > 
> > No. The PMD is doing the relation between the PCI device and the ethdev port.
> 
> It seems that the ethdev layer can create eth devices based on 
> rte_pci_device, but does not release rte_pci_device.

No, the ethdev layer does not manage any bus.
Only the PMD does that.

> >> And the rte_pci_device corresponding to the eth devices managed and
> >> processed by rte_pci_bus.
> >>
> >> So, PMD is closed only based on the port ID of the eth device, whilch
> >> only shuts down eth devices, not frees rte_pci_device
> >> and remove it from rte_pci_bus.
> > Not really.
> I do not see any PMD driver releasing rte_pci_device in dev_close().

Maybe not but we should.

> > If there is no port using the PCI device, it should be released.
> 
> Yes.
> >
> >>>> As far as I know, most apps or examples in the DPDK project have only
> >>>> one port for a pci device.
> >>> The number of ports per PCI device is driver-specific.
> >>>
> >>>> When the port is closed, the rte_pci_device should be freed. But none of
> >>>> the apps seem to do this.
> >>> That's because from the app point of view, only ports should be managed.
> >>> The hardware device is managed by the PMD.
> >>> Only drivers (PMDs) have to do the relation between class ports
> >>> and hardware devices.
> >> 
> >> Yes. But the current app only closes the port to disable the PMD, and
> >> the rte_pci_device cannot be freed.
> > 
> > Why not?
> 
> Because most apps in DPDK call dev_close() to close the eth device 
> corresponding to a port.

You don't say why the underlying PCI device could not be freed.

> >> Because rte_pci_device cannot be released in dev_close() of PMD, and is
> >> managed by framework layer.
> > 
> > No
> >
> >> Btw. Excluding rte_dev_probe() and rte_dev_remove(),  it seems that the
> >> DPDK framework only automatically
> >> scans PCI devices, but does not automatically release PCI devices when
> >> the process exits.
> > 
> > Indeed, because such freeing is the responsibility of the PMD.
> 
> Do you mean to free rte_pci_device in the dev_close() API?

I mean free the PCI device in the PMD implementation of dev_close.

> How should PMD free it? What should we do? Any good suggestions?

Check that there is no other port sharing the same PCI device,
then call the PMD callback for rte_pci_remove_t.

> Would it be more appropriate to do this in rte_eal_cleanup() if it 
> cann't be done in the API above?

rte_eal_cleanup is a last cleanup for what was not done earlier.
We could do that but first we should properly free devices when closed.