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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id fb4-20020a1709073a0400b00a1c76114fcesm7513801ejc.218.2023.12.13.02.05.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Dec 2023 02:05:58 -0800 (PST) Date: Wed, 13 Dec 2023 11:05:56 +0100 From: Igor Mammedov To: Dongli Zhang Cc: linux-acpi@vger.kernel.org, linux-pci@vger.kernel.org, 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 , Thomas Lamprecht , linux-kernel@vger.kernel.org Subject: Re: [RFC 2/2] PCI: acpiphp: slowdown hotplug if hotplugging multiple devices at a time Message-ID: <20231213110556.5f1d83bf@imammedo.users.ipa.redhat.com> In-Reply-To: References: <20231213003614.1648343-1-imammedo@redhat.com> <20231213003614.1648343-3-imammedo@redhat.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 Dec 2023 00:13:37 -0800 Dongli Zhang wrote: > 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? qemu example would be: {qemu) stop (qemu) device_add device_add vhost-scsi-pci,wwpn=naa.5001405324af0985,id=vhost01,bus=bridge1,addr=8 (qemu) device_add vhost-scsi-pci,wwpn=naa.5001405324af0986,id=vhost02,bus=bridge1,addr=0 (qemu) cont this way when machine continues to run acpiphp code will see 2 HBAs at once and try to process one right after another. So [1/2] patch is not enough to cover above case, and hence the same hack SHPC employs by adding delay. However 2 separate hotplug events as in your reproducer should be covered by the 1st patch. > 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 > > --- > > 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 > > #include > > #include > > +#include > > > > #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 { >