Re: [RFC 2/2] PCI: acpiphp: slowdown hotplug if hotplugging multiple devices at a time

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Dec 13, 2023 at 01:36:14AM +0100, Igor Mammedov wrote:
> previous commit ("PCI: acpiphp: enable slot only if it hasn't been enabled already"
> introduced a workaround to avoid a race between SCSI_SCAN_ASYNC job and
> bridge reconfiguration in case of single HBA hotplug.
> However in virt environment it's possible to pause machine hotplug several
> HBAs and let machine run. That can hit the same race when 2nd hotplugged
> HBA will start re-configuring bridge.
> Do the same thing as SHPC and throttle down hotplug of 2nd and up
> devices within single hotplug event.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  drivers/pci/hotplug/acpiphp_glue.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
> index 6b11609927d6..30bca2086b24 100644
> --- a/drivers/pci/hotplug/acpiphp_glue.c
> +++ b/drivers/pci/hotplug/acpiphp_glue.c
> @@ -37,6 +37,7 @@
>  #include <linux/mutex.h>
>  #include <linux/slab.h>
>  #include <linux/acpi.h>
> +#include <linux/delay.h>
>  
>  #include "../pci.h"
>  #include "acpiphp.h"
> @@ -700,6 +701,7 @@ static void trim_stale_devices(struct pci_dev *dev)
>  static void acpiphp_check_bridge(struct acpiphp_bridge *bridge)
>  {
>  	struct acpiphp_slot *slot;
> +        int nr_hp_slots = 0;
>  
>  	/* Bail out if the bridge is going away. */
>  	if (bridge->is_going_away)
> @@ -723,6 +725,10 @@ static void acpiphp_check_bridge(struct acpiphp_bridge *bridge)
>  
>  			/* configure all functions */
>  			if (slot->flags != SLOT_ENABLED) {
> +				if (nr_hp_slots)
> +					msleep(1000);
> +
> +                                ++nr_hp_slots;
>  				enable_slot(slot, true);
>  			}
>  		} else {
> -- 
> 2.39.3
> 
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>