linux-kernel - Re: [PATCH V5 3/3] PCI: Mask and unmask hotplug interrupts during reset

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Message-ID: <20180703083447.GA2689@wunner.de>
Date:   Tue, 3 Jul 2018 10:34:47 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Oza Pawandeep <poza@...eaurora.org>,
        Keith Busch <keith.busch@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5 3/3] PCI: Mask and unmask hotplug interrupts during
 reset

On Mon, Jul 02, 2018 at 06:52:47PM -0400, Sinan Kaya wrote:
> If a bridge supports hotplug and observes a PCIe fatal error, the following
> events happen:
> 
> 1. AER driver removes the devices from PCI tree on fatal error
> 2. AER driver brings down the link by issuing a secondary bus reset waits
> for the link to come up.
> 3. Hotplug driver observes a link down interrupt
> 4. Hotplug driver tries to remove the devices waiting for the rescan lock
> but devices are already removed by the AER driver and AER driver is waiting
> for the link to come back up.
> 5. AER driver tries to re-enumerate devices after polling for the link
> state to go up.
> 6. Hotplug driver obtains the lock and tries to remove the devices again.
> 
> If a bridge is a hotplug capable bridge, mask hotplug interrupts before the
> reset and unmask afterwards.

Would it work for you if you just amended the AER driver to skip
removal and re-enumeration of devices if the port is a hotplug bridge?
Just check for is_hotplug_bridge in struct pci_dev.

That would seem like a much simpler solution, given that it is known
that the link will flap on reset, causing the hotplug driver to remove
and re-enumerate devices.  That would also cover cases where hotplug is
handled by a different driver than pciehp, or by the platform firmware.

Thanks,

Lukas