Re: [PATCH v8 10/12] PCI: liveupdate: Freeze preservation status during shutdown

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Jul 28, 2026 at 10:10:04PM +0000, David Matlack wrote:
> Freeze a device's outgoing preservation status (preserved or not
> preserved) during shutdown. This enables the PCI core and drivers to
> safely make decisions based on the device's preservation status during
> shutdown.
> 
> Note that pci_liveupdate_freeze() is triggered by the PCI core rather
> than from drivers participating in Live Update so that all devices can
> have their status frozen (i.e. prevent non-preserved devices from
> getting preserved late).

This calls pci_liveupdate_freeze() from pci_device_shutdown(), the
pci_bus_type .shutdown() method, which I think is only called from
device_shutdown() in the kexec or restart paths.

Since there's no error exit after we get as far as device_shutdown(),
and this applies to all devices and dev->liveupdate.frozen is never
set to false (at least at this point in the series), is there benefit
to tracking this per-device?

> Reviewed-by: Pranjal Shrivastava <praan@google.com>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Signed-off-by: David Matlack <dmatlack@google.com>

Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/liveupdate.c       | 16 ++++++++++++++++
>  drivers/pci/liveupdate.h       |  4 ++++
>  drivers/pci/pci-driver.c       |  2 ++
>  include/linux/pci_liveupdate.h |  3 +++
>  4 files changed, 25 insertions(+)
> 
> diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
> index 744513ee11ed..65bcecb1b64e 100644
> --- a/drivers/pci/liveupdate.c
> +++ b/drivers/pci/liveupdate.c
> @@ -394,6 +394,11 @@ static int pci_liveupdate_unpreserve_device(struct pci_flb_outgoing *outgoing,
>  {
>  	struct pci_dev_ser *dev_ser = dev->liveupdate.outgoing;
>  
> +	if (dev->liveupdate.frozen) {
> +		pci_warn(dev, "Cannot unpreserve device after it is frozen!\n");
> +		return -EINVAL;
> +	}
> +
>  	if (!dev_ser) {
>  		pci_warn(dev, "Cannot unpreserve device that is not preserved\n");
>  		return -EINVAL;
> @@ -447,6 +452,11 @@ static int pci_liveupdate_preserve_device(struct pci_flb_outgoing *outgoing,
>  		return -EINVAL;
>  	}
>  
> +	if (dev->liveupdate.frozen) {
> +		pci_warn(dev, "Cannot preserve device after it is frozen!\n");
> +		return -EINVAL;
> +	}
> +
>  	if (dev->liveupdate.outgoing) {
>  		if (!dev->liveupdate.outgoing->refcount) {
>  			pci_WARN(dev, 1, "Preserved device with 0 refcount!\n");
> @@ -718,6 +728,12 @@ void pci_liveupdate_cleanup_device(struct pci_dev *dev)
>  		pci_WARN(dev, 1, "Destroying incoming-preserved device!\n");
>  }
>  
> +void pci_liveupdate_freeze(struct pci_dev *dev)
> +{
> +	guard(rwsem_write)(&pci_liveupdate.rwsem);
> +	dev->liveupdate.frozen = 1;

Nit, the series assigns "true" to other booleans
(preserve_bus_numbers, was_preserved).

> +}
> +
>  static int pci_liveupdate_finish_device(struct pci_ser *ser, struct pci_dev *dev)
>  {
>  	if (!dev->liveupdate.incoming) {
> diff --git a/drivers/pci/liveupdate.h b/drivers/pci/liveupdate.h
> index ccc23031e99d..49d07fd02132 100644
> --- a/drivers/pci/liveupdate.h
> +++ b/drivers/pci/liveupdate.h
> @@ -13,6 +13,7 @@
>  #ifdef CONFIG_PCI_LIVEUPDATE
>  void pci_liveupdate_setup_device(struct pci_dev *dev);
>  void pci_liveupdate_cleanup_device(struct pci_dev *dev);
> +void pci_liveupdate_freeze(struct pci_dev *dev);
>  bool pci_liveupdate_preserve_bus_numbers(struct pci_bus *bus,
>  					 struct pci_dev *dev);
>  void pci_liveupdate_scan_bridge_end(struct pci_dev *dev);
> @@ -28,6 +29,9 @@ static inline void pci_liveupdate_cleanup_device(struct pci_dev *dev)
>  {
>  }
>  
> +static inline void pci_liveupdate_freeze(struct pci_dev *dev)
> +{
> +}
>  static inline bool pci_liveupdate_preserve_bus_numbers(struct pci_bus *bus,
>  						       struct pci_dev *dev)
>  {
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index f36778e62ac1..51616e4327d3 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -21,6 +21,7 @@
>  #include <linux/acpi.h>
>  #include <linux/dma-map-ops.h>
>  #include <linux/iommu.h>
> +#include "liveupdate.h"
>  #include "pci.h"
>  #include "pcie/portdrv.h"
>  
> @@ -536,6 +537,7 @@ static void pci_device_shutdown(struct device *dev)
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	struct pci_driver *drv = pci_dev->driver;
>  
> +	pci_liveupdate_freeze(pci_dev);
>  	pm_runtime_resume(dev);
>  
>  	if (drv && drv->shutdown)
> diff --git a/include/linux/pci_liveupdate.h b/include/linux/pci_liveupdate.h
> index 04a2b2a3102a..31898685a406 100644
> --- a/include/linux/pci_liveupdate.h
> +++ b/include/linux/pci_liveupdate.h
> @@ -24,6 +24,8 @@
>   * @was_preserved: True if this struct pci_dev was preserved by the previous
>   *                 kernel. Unlike @incoming, this field is not cleared after
>   *                 the device is finished participating in Live Update.
> + * @frozen: True if the outgoing preservation status of this device is frozen
> + *          and thus cannot be changed.
>   */
>  struct pci_liveupdate {
>  	struct pci_dev_ser *outgoing;
> @@ -31,6 +33,7 @@ struct pci_liveupdate {
>  	u16 acs_ctrl;
>  	bool preserve_bus_numbers;
>  	bool was_preserved;
> +	bool frozen;
>  };
>  
>  struct pci_dev;
> -- 
> 2.55.0.487.gaf234c4eb3-goog
>