Re: [PATCH 5.10 STABLE] s390/pci: fix zpci_zdev_put() on reserve

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Oct 12, 2021 at 11:34:25AM +0200, Niklas Schnelle wrote:
> [ Upstream commit a46044a92add6a400f4dada7b943b30221f7cc80 ]
> 
> Since commit 2a671f77ee49 ("s390/pci: fix use after free of zpci_dev")
> the reference count of a zpci_dev is incremented between
> pcibios_add_device() and pcibios_release_device() which was supposed to
> prevent the zpci_dev from being freed while the common PCI code has
> access to it. It was missed however that the handling of zPCI
> availability events assumed that once zpci_zdev_put() was called no
> later availability event would still see the device. With the previously
> mentioned commit however this assumption no longer holds and we must
> make sure that we only drop the initial long-lived reference the zPCI
> subsystem holds exactly once.
> 
> Do so by introducing a zpci_device_reserved() function that handles when
> a device is reserved. Here we make sure the zpci_dev will not be
> considered for further events by removing it from the zpci_list.
> 
> This also means that the device actually stays in the
> ZPCI_FN_STATE_RESERVED state between the time we know it has been
> reserved and the final reference going away. We thus need to consider it
> a real state instead of just a conceptual state after the removal. The
> final cleanup of PCI resources, removal from zbus, and destruction of
> the IOMMU stays in zpci_release_device() to make sure holders of the
> reference do see valid data until the release.

Same for the 5.14 patch, please submit the series that resolves this,
not changing individual patches a lot.

thanks,

greg k-h