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From:   Igor Mammedov <imammedo@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Dongli Zhang <dongli.zhang@oracle.com>, linux-acpi@vger.kernel.org,
        linux-pci@vger.kernel.org, imammedo@redhat.com, mst@redhat.com,
        rafael@kernel.org, lenb@kernel.org, bhelgaas@google.com,
        mika.westerberg@linux.intel.com, boris.ostrovsky@oracle.com,
        joe.jin@oracle.com, stable@vger.kernel.org,
        Fiona Ebner <f.ebner@proxmox.com>,
        Thomas Lamprecht <t.lamprecht@proxmox.com>
Subject: [RFC 2/2] PCI: acpiphp: slowdown hotplug if hotplugging multiple devices at a time
Date:   Wed, 13 Dec 2023 01:36:14 +0100
Message-Id: <20231213003614.1648343-3-imammedo@redhat.com>
In-Reply-To: <20231213003614.1648343-1-imammedo@redhat.com>
References: <20231213003614.1648343-1-imammedo@redhat.com>
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Precedence: bulk

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