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Message-ID: <501c1078-ef45-4469-87f8-32525d6f2608@proxmox.com>
Date:   Wed, 13 Dec 2023 10:47:27 +0100
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Subject: Re: [RFC 1/2] PCI: acpiphp: enable slot only if it hasn't been
 enabled already
To:     Igor Mammedov <imammedo@redhat.com>, linux-kernel@vger.kernel.org
Cc:     Dongli Zhang <dongli.zhang@oracle.com>, 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,
        Thomas Lamprecht <t.lamprecht@proxmox.com>
References: <20231213003614.1648343-1-imammedo@redhat.com>
 <20231213003614.1648343-2-imammedo@redhat.com>
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From:   Fiona Ebner <f.ebner@proxmox.com>
In-Reply-To: <20231213003614.1648343-2-imammedo@redhat.com>
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Am 13.12.23 um 01:36 schrieb Igor Mammedov:
> When SCSI_SCAN_ASYNC is enabled (either via config or via cmd line),
> adding device to bus and enabling it will kick in async host scan
> 
>  scsi_scan_host+0x21/0x1f0
>  virtscsi_probe+0x2dd/0x350
>  ..
>  driver_probe_device+0x19/0x80
>  ...
>  driver_probe_device+0x19/0x80
>  pci_bus_add_device+0x53/0x80
>  pci_bus_add_devices+0x2b/0x70
>  ...
> 
> which will schedule a job for async scan. That however breaks
> if there are more than one SCSI host behind bridge, since
> acpiphp_check_bridge() will walk over all slots and try to
> enable each of them regardless of whether they were already
> enabled.
> As result the bridge might be reconfigured several times
> and trigger following sequence:
> 
>   [cpu 0] acpiphp_check_bridge()
>   [cpu 0]   enable_slot(a)
>   [cpu 0]     configure bridge
>   [cpu 0]     pci_bus_add_devices() -> scsi_scan_host(a1)
>   [cpu 0]   enable_slot(b)
>   ...
>   [cpu 1] do_scsi_scan_host(a1) <- async jib scheduled for slot a
>   ...
>   [cpu 0]     configure bridge <- temporaly disables bridge
> 
> and cause do_scsi_scan_host() failure.
> The same race affects SHPC (but it manages to avoid hitting the race due to
> 1sec delay when enabling slot).
> To cover case of single device hotplug (at a time) do not attempt to
> enable slot that have already been enabled.
> 
> Fixes: 40613da52b13 ("PCI: acpiphp: Reassign resources on bridge if necessary")
> Reported-by: Dongli Zhang <dongli.zhang@oracle.com>
> Reported-by: iona Ebner <f.ebner@proxmox.com>

Missing an F here ;)

> Signed-off-by: Igor Mammedov <imammedo@redhat.com>

Thank you! Works for me:

Tested-by: Fiona Ebner <f.ebner@proxmox.com>