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

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Message-ID: <20231213110729.3845f530@imammedo.users.ipa.redhat.com>
Date:   Wed, 13 Dec 2023 11:07:29 +0100
From:   Igor Mammedov <imammedo@...hat.com>
To:     Fiona Ebner <f.ebner@...xmox.com>
Cc:     linux-kernel@...r.kernel.org,
        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

On Wed, 13 Dec 2023 10:47:27 +0100
Fiona Ebner <f.ebner@...xmox.com> wrote:

> 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 ;)

Sorry for copypaste mistake, I'll fix it up on the next submission.

> 
> > Signed-off-by: Igor Mammedov <imammedo@...hat.com>  
> 
> Thank you! Works for me:
> 
> Tested-by: Fiona Ebner <f.ebner@...xmox.com>
>