linux-kernel - Re: [PATCH v2] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected

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Date:   Thu, 27 Dec 2018 19:28:55 +0000
From:   <Alex_Gagniuc@...lteam.com>
To:     <helgaas@...nel.org>, <mr.nuke.me@...il.com>
Cc:     <linux-pci@...r.kernel.org>, <keith.busch@...el.com>,
        <Austin.Bolen@...l.com>, <Shyam.Iyer@...l.com>,
        <linux-kernel@...r.kernel.org>, <jonathan.derrick@...el.com>,
        <gregkh@...uxfoundation.org>, <lukas@...ner.de>,
        <ruscur@...sell.cc>, <sbobroff@...ux.ibm.com>, <oohall@...il.com>,
        <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2] PCI/MSI: Don't touch MSI bits when the PCI device is
 disconnected

On 11/8/18 2:09 PM, Bjorn Helgaas wrote:
> 
> [EXTERNAL EMAIL]
> Please report any suspicious attachments, links, or requests for sensitive information.
> 
> 
> [+cc Jonathan, Greg, Lukas, Russell, Sam, Oliver for discussion about
> PCI error recovery in general]
> 
> On Wed, Nov 07, 2018 at 05:42:57PM -0600, Bjorn Helgaas wrote:
>> On Tue, Sep 18, 2018 at 05:15:00PM -0500, Alexandru Gagniuc wrote:
>>> When a PCI device is gone, we don't want to send IO to it if we can
>>> avoid it. We expose functionality via the irq_chip structure. As
>>> users of that structure may not know about the underlying PCI device,
>>> it's our responsibility to guard against removed devices.
>>>
>>> .irq_write_msi_msg() is already guarded inside __pci_write_msi_msg().
>>> .irq_mask/unmask() are not. Guard them for completeness.
>>>
>>> For example, surprise removal of a PCIe device triggers teardown. This
>>> touches the irq_chips ops some point to disable the interrupts. I/O
>>> generated here can crash the system on firmware-first machines.
>>> Not triggering the IO in the first place greatly reduces the
>>> possibility of the problem occurring.
>>>
>>> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
>>
>> Applied to pci/misc for v4.21, thanks!
> 
> I'm having second thoughts about this. 

Do we have a verdict on this? If you don't like this approach, then I'll 
have to fix the problem in some other way, but the problem still needs 
to be fixed.

Alex