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Date:   Sat, 15 Oct 2022 17:36:00 +0200
From:   "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
To:     "Bhatnagar, Rishabh" <risbhat@amazon.com>
Cc:     "Herrenschmidt, Benjamin" <benh@amazon.com>,
        "sashal@kernel.org" <sashal@kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Bacco, Mike" <mbacco@amazon.com>
Subject: Re: [PATCH 0/6] IRQ handling patches backport to 4.14 stable
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On Fri, Oct 14, 2022 at 12:00:31PM -0700, Bhatnagar, Rishabh wrote:
> 
> On 10/9/22 10:50 AM, Bhatnagar, Rishabh wrote:
> > 
> > On 10/6/22 8:07 PM, Herrenschmidt, Benjamin wrote:
> > > (putting my @amazon.com 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).
> > Yes these patches were tested on multiple virt/metal EC2 instances.
> > > 
> > > 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 :-)
> > > 
> > > Cheers,
> > > Ben.
> > > 
> Hi Greg
> 
> Let us know if you think it would be beneficial to take these backports for
> 4.14 stable.

Give me some time after -rc1 is out to review this then as we are
swamped right now.

> We can drop this patch set otherwise.

You can do whatever you want with your tree :)

thanks,

greg k-h