Re: [cxl:pending 13/21] drivers/cxl/pci.c:511:8-33: WARNING: Threaded IRQ with no primary handler requested without IRQF_ONESHOT (unless it is nested IRQ)

[Ira Weiny <ira.weiny@intel.com>]

Davidlohr Bueso wrote:
> On Tue, 31 Jan 2023, Dan Williams wrote:
> 
> >Ira Weiny wrote:
> >[..]
> >> > Considering MSIs are edge triggered interrupts, this should be benign.
> >>
> >> I'm trying to understand this a bit more.  So I looked in more detail.  I
> >> believe Dan suggested that I could use irq_default_primary_handler() in
> >> this case by passing NULL.  And this would handle threading the irq
> >> processing for me.
> >>
> >> It looks from a software standpoint this should work.  But the kdocs
> >> really imply that not masking the irq in the handler may be an issue.
> >> Thus the 'requirement' of using IRQF_ONESHOT.
> >>
> >> Is this somehow different with MSI?  Is this a case of the kdocs being a
> >> bit out of date for MSI?
> >
> >My reading, may be from the changelog and not the kdocs, was that at
> >request_irq() time it is difficult to discern level triggered vs
> >edge-triggered. So for the default primary handler, that does nothing to
> >quiet a screaming level-triggered interrupt, just require oneshot mode.
> 
> Right and it's only level-triggered that are the problem after done with
> the hardirq handler. So in the msi/cxl case we already know that all this
> is edge (sent once and forgotten by the hardware), which is why I was saying
> it's harmless. It's still probably a good idea to have it explicitly oneshot
> semantics as Dan's patch.

Ok that makes sense.

Thanks to you both for clarifying and to Dan for the patch.

Ira