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

[Alex_Gagniuc]

On 11/08/2018 04:51 PM, Greg KH wrote:
> On Thu, Nov 08, 2018 at 10:49:08PM +0000, Alex_Gagniuc@xxxxxxxxxxxx wrote:
>> In the case that we're trying to fix, this code executing is a result of
>> the device being gone, so we can guarantee race-free operation. I agree
>> that there is a race, in the general case. As far as checking the result
>> for all F's, that's not an option when firmware crashes the system as a
>> result of the mmio read/write. It's never pretty when firmware gets
>> involved.
> 
> If you have firmware that crashes the system when you try to read from a
> PCI device that was hot-removed, that is broken firmware and needs to be
> fixed.  The kernel can not work around that as again, you will never win
> that race.

But it's not the firmware that crashes. It's linux as a result of a 
fatal error message from the firmware. And we can't fix that because FFS 
handling requires that the system reboots [1].

If we're going to say that we don't want to support FFS because it's a 
separate code path, and different flow, that's fine. I am myself, not a 
fan of FFS. But if we're going to continue supporting it, I think we'll 
continue to have to resolve these sort of unintended consequences.

Alex

[1] ACPI 6.2, 18.1 - Hardware Errors and Error Sources