Re: [PATCH 0/6] IRQ handling patches backport to 4.14 stable

From: Herrenschmidt, Benjamin
Date: Thu Oct 06 2022 - 23:08:20 EST

(putting my hat on)

On Sun, 2022-10-02 at 17:30 +0200, Greg KH wrote:

> On Thu, Sep 29, 2022 at 09:06:45PM +0000, Rishabh Bhatnagar wrote:
> > This patch series backports a bunch of patches related IRQ handling
> > with respect to freeing the irq line while IRQ is in flight at CPU
> > or at the hardware level.
> > Recently we saw this issue in serial 8250 driver where the IRQ was
> > being
> > freed while the irq was in flight or not yet delivered to the CPU.
> > As a
> > result the irqchip was going into a wedged state and IRQ was not
> > getting
> > delivered to the cpu. These patches helped fixed the issue in 4.14
> > kernel.
> Why is the serial driver freeing an irq while the system is running?
> Ah, this could happen on a tty hangup, right?

Right. Rishabh answered that separately.

> > Let us know if more patches need backporting.
> What hardware platform were these patches tested on to verify they
> work properly?  And why can't they move to 4.19 or newer if they
> really need this fix?  What's preventing that?
> As Amazon doesn't seem to be testing 4.14.y -rc releases, I find it
> odd that you all did this backport.  Is this a kernel that you all
> care about?

These were tested on a collection of EC2 instances, virtual and metal I
believe (Rishabh, please confirm).

Amazon Linux 2 runs 4.14 or 5.10. Unfortunately we still have to
support customers running the former.

We'll be including these patches in our releases, we thought it would
be nice to have them in -stable as well for the sake of whoever else
might be still using this kernel. No huge deal if they don't.

As for testing -rc's, yes, we need to get better at that (and publish
what we test). Point taken :-)