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Date:   Fri, 14 Oct 2022 12:00:31 -0700
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Subject: Re: [PATCH 0/6] IRQ handling patches backport to 4.14 stable
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From:   "Bhatnagar, Rishabh" <risbhat@amazon.com>
To:     "Herrenschmidt, Benjamin" <benh@amazon.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
CC:     "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>
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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.
We can drop this patch set otherwise.

Thanks alot,
Rishabh