linux-kernel - Re: [RFC 1/2] PCI: acpiphp: enable slot only if it hasn't been enabled already

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Message-ID: <501c1078-ef45-4469-87f8-32525d6f2608@proxmox.com>
Date:   Wed, 13 Dec 2023 10:47:27 +0100
From:   Fiona Ebner <f.ebner@...xmox.com>
To:     Igor Mammedov <imammedo@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Dongli Zhang <dongli.zhang@...cle.com>, 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,
        Thomas Lamprecht <t.lamprecht@...xmox.com>
Subject: Re: [RFC 1/2] PCI: acpiphp: enable slot only if it hasn't been
 enabled already

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@...cle.com>
> Reported-by: iona Ebner <f.ebner@...xmox.com>

Missing an F here ;)

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

Thank you! Works for me:

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