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

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Date:   Tue, 3 Jul 2018 16:17:50 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     poza@...eaurora.org
Cc:     Sinan Kaya <okaya@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        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 Tue, Jul 03, 2018 at 07:40:46PM +0530, poza@...eaurora.org wrote:
> On 2018-07-03 19:29, Lukas Wunner wrote:
> >On Tue, Jul 03, 2018 at 09:31:24AM -0400, Sinan Kaya wrote:
> >>Issue is observing hotplug link down event in the middle of AER recovery
> >>as in my previous reply.
> >>
> >>If we mask hotplug interrupts before secondary bus reset via my patch,
> >>then hotplug driver will not observe both link up and link down
> >>interrupts.
> >>
> >>If we don't mask hotplug interrupts, we have a race condition.
> >
> >I assume that a bus reset not only causes a link and presence event but
> >also clears the Presence Detect State bit in the Slot Status register
> >and the Data Link Layer Link Active bit in the Link Status register
> >momentarily.
> >
> >pciehp may access those two bits concurrently to the AER driver
> >performing a slot reset.  So it may not be sufficient to mask
> >the interrupt.
> >
> >I've posted this patch to address the issue:
> >https://patchwork.ozlabs.org/patch/930391/
> 
> Was just wondering that you are protecting Presence Detect State bit with
> reset_lock, mainly in pciehp_ist
> but with hotplug interrupt disabled, is there another way that it hotplug
> code gets activated ?

The user may turn the slot on/off via sysfs.  If an Attention Button
is present, the user may also press that button to turn the slot on/off
after 5 seconds.  Either way, it may cause pciehp's IRQ thread to run
concurrently to a reset initiated by the AER driver, independently of
any events signalled by the slot.

Thanks,

Lukas