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

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Message-ID: <d93c4614-1bbc-3a30-305e-28ff75d7fde2@oracle.com>
Date:   Wed, 13 Dec 2023 00:13:37 -0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     Igor Mammedov <imammedo@...hat.com>
Cc:     linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        mst@...hat.com, rafael@...nel.org, lenb@...nel.org,
        bhelgaas@...gle.com, mika.westerberg@...ux.intel.com,
        boris.ostrovsky@...cle.com, joe.jin@...cle.com,
        stable@...r.kernel.org, Fiona Ebner <f.ebner@...xmox.com>,
        Thomas Lamprecht <t.lamprecht@...xmox.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] PCI: acpiphp: slowdown hotplug if hotplugging multiple
 devices at a time

Hi Igor,


On 12/12/23 16:36, 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

Would you mind helping explain what does "pause machine hotplug several HBAs and
let machine run" indicate?

Thank you very much!

Dongli Zhang

> 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@...hat.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 {