linux-kernel - Re: [RFC 0/2] PCI: acpiphp: workaround race between hotplug and SCSI_SCAN

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Date:   Wed, 13 Dec 2023 19:12:51 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Igor Mammedov <imammedo@...hat.com>, 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, Fiona Ebner <f.ebner@...xmox.com>,
        Thomas Lamprecht <t.lamprecht@...xmox.com>
Subject: Re: [RFC 0/2] PCI: acpiphp: workaround race between hotplug and
 SCSI_SCAN_ASYNC job

On Wed, Dec 13, 2023 at 7:11 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Wed, Dec 13, 2023 at 01:36:12AM +0100, Igor Mammedov wrote:
> > Hacks to mask a race between HBA scan job and bridge re-configuration(s)
> > during hotplug.
> >
> > I don't like it a bit but it something that could be done quickly
> > and solves problems that were reported.
>
> I agree, I don't like it either.  Adding a 1s delay doesn't address
> the real problem, and putting in a band-aid like this means the real
> problem would likely never be addressed.
>
> At this point the best option I see is to revert these:
>
>   cc22522fd55e2 ("PCI: acpiphp: Use pci_assign_unassigned_bridge_resources() only for non-root bus")
>   40613da52b13f ("PCI: acpiphp: Reassign resources on bridge if necessary")
>
> I hate the fact that reverting them would mean the root bus hotplug
> and ACPI bus check notifications would become issues again.
>
> But keeping these commits even though they add a new different problem
> that breaks things for somebody else seems worse to me.

Agreed.