Re: [PATCH 14/16] pciehp: Ignore link events during DPC event

[Keith Busch <keith.busch@intel.com>]

On Sun, Sep 02, 2018 at 04:27:14PM +0200, Lukas Wunner wrote:
> On Fri, Aug 31, 2018 at 03:26:37PM -0600, Keith Busch wrote:
> > This patch adds a channel state to a subordinate bus. When a DPC event is
> > triggered, the DPC driver will set the channel state to frozen, and the
> > pciehp driver will ignore link events if the subordinate bus is being
> > managed by DPC error handling.
> > 
> > This is safe because the pciehp and DPC drivers share the same
> > interrupt. The DPC driver sets the bus state in the top-half interrupt
> > context, and the pciehp driver checks and masks off link events in its
> > bottom-half error handler.
> 
> I really liked Sinan's approach of checking in pciehp whether a fatal
> error is pending and waiting for it to be handled:
> https://patchwork.ozlabs.org/patch/959464/
> 
> This seemed to avoid any races with DPC and is small and simple.
> Can we pursue a solution along those lines?

That introduces a completely different race between the error handling
and hotplug threads. We don't control  which interrupt fires first or
any way ensure they're even the same event.