linux-kernel - Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with clocks gated

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Message-ID: <20210701135949.GA51123@bjorn-Precision-5520>
Date:   Thu, 1 Jul 2021 08:59:49 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Robinson <pbrobinson@...il.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Michal Simek <michal.simek@...inx.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with
 clocks gated

On Thu, Jul 01, 2021 at 12:09:58AM +0200, Javier Martinez Canillas wrote:
> On 6/30/21 10:30 PM, Bjorn Helgaas wrote:
> > On Wed, Jun 30, 2021 at 09:59:58PM +0200, Javier Martinez Canillas wrote:
> 
> [snip]
> 
> >> But maybe you can also add a paragraph that mentions the
> >> CONFIG_DEBUG_SHIRQ option and shared interrupts? That way, other
> >> driver authors could know that by enabling this an underlying
> >> problem might be exposed for them to fix.
> > 
> > Good idea, thanks!  I added this; is it something like what you
> > had in mind?
> 
> Thanks a lot for doing this rewording. I just have a small nit for
> the text.
> 
> >     Found by enabling CONFIG_DEBUG_SHIRQ, which calls the IRQ
> >     handler when it is being unregistered.  An error during the
> >     probe path might cause this unregistration and IRQ handler
> >     execution before the device or data structure init has
> >     finished.
> 
> The IRQ handler is not called when unregistered, but it is called
> when another handler for the shared IRQ is unregistered. In this
> particular driver, both a "pcie-sys" and "pcie-client" handlers are
> registered, then an error leads to "pcie-sys" being unregistered and
> the handler for "pcie-client" being called.

Is this really true?  I think that would mean CONFIG_DEBUG_SHIRQ would
not find this kind of bug unless we actually registered two or more
handlers for the shared IRQ, but it's still a bug even only one
handler is registered.

Looking at __free_irq() [1], my impression is that "action" is what
we're removing and action->handler() is the IRQ handler we call when
CONFIG_DEBUG_SHIRQ, so it doesn't look like it's calling the remaining
handlers after removing one of them.

> So maybe the following instead?
> 
>     Found by enabling CONFIG_DEBUG_SHIRQ, which calls the IRQ
>     handlers when a handler for the shared IRQ is unregistered. An
>     error during the probe path might cause this unregistration and
>     handler execution before the device or data structure init has
>     finished.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/irq/manage.c?id=v5.13#n1805