Date:   Thu, 16 Apr 2020 19:31:25 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "gerlitz.or@...il.com" <gerlitz.or@...il.com>
CC:     "sashal@...nel.org" <sashal@...nel.org>,
        "ecree@...arflare.com" <ecree@...arflare.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH AUTOSEL 4.9 09/26] net/mlx5e: Init ethtool steering for
 representors

On Thu, 2020-04-16 at 19:20 +0200, Greg KH wrote:
> On Thu, Apr 16, 2020 at 04:40:31PM +0300, Or Gerlitz wrote:
> > On Thu, Apr 16, 2020 at 3:00 AM Sasha Levin <sashal@...nel.org>
> > wrote:
> > > I'd maybe point out that the selection process is based on a
> > > neural
> > > network which knows about the existence of a Fixes tag in a
> > > commit.
> > > 
> > > It does exactly what you're describing, but also taking a bunch
> > > more
> > > factors into it's desicion process ("panic"? "oops"? "overflow"?
> > > etc).
> > 
> > As Saeed commented, every extra line in stable / production kernel
> > is wrong.
> 
> What?  On what do you base that crazy statement on?  I have 18+ years
> of
> direct experience of that being the exact opposite.
> 

Oh, I never said such a thing .. :( 

I think Or meant to say: every extra line that no one asked for.

And all i wanted to say is that it can have a catastrophic result..
I know in many cases it is working well, and i didn't say it is wrong,
I am just worried about it and wanted to show an example of how it can
screw up under the radar with a simple single liner patch.. 

> > IMHO it doesn't make any sense to take into stable automatically
> > any patch that doesn't have fixes line. Do you have 1/2/3/4/5
> > concrete
> > examples from your (referring to your Microsoft employee hat
> > comment
> > below) or other's people production environment where patches
> > proved to
> > be necessary but they lacked the fixes tag - would love to see
> > them.
> 
> Oh wow, where do you want me to start.  I have zillions of these.
> 
> But wait, don't trust me, trust a 3rd party.  Here's what Google's
> security team said about the last 9 months of 2019:
> 	- 209 known vulnerabilities patched in LTS kernels, most
> without
> 	  CVEs
> 	- 950+ criticial non-security bugs fixes for device XXXX alone
> 	  with LTS releases
> 

So opt-in for these critical or _always_ in use basic kernel sections.
but make the default opt-out.. 

> > We've been coaching new comers for years during internal and on-
> > list
> > code reviews to put proper fixes tag. This serves (A) for the
> > upstream
> > human review of the patch and (B) reasonable human stable
> > considerations.
> 
> If your driver/subsystem is doing this, wonderful, just opt-out of
> the
> autosel process and you will never be bothered again.
> 

There are many legacy devices in the kernel that are not well
maintained and being rarely fixed from random users.. if a fix will be
picked up to the wrong kernel, it can go unnoticed for years.. 

> But, trust me, I think I know a bit about tagging stuff for stable
> kernels, and yet the AUTOSEL tool keeps finding patches that _I_
> forgot
> to tag as such.  So, don't be so sure of yourself, it's humbling :)
> 
> Let the AUTOSEL tool run, and if it finds things you don't agree
> with, a
> simple "No, please do not include this" email is all you need to do
> to
> keep it out of a stable kernel.
> 
> So far the AUTOSEL tool has found so many real bugfixes that it isn't
> funny.  If you don't like it, fine, but it has proven itself _way_
> beyond my wildest hopes already, and it just keeps getting better.
> 

Now i really don't know what the right balance here, in on one hand,
autosel is doing a great job, on the other hand we know it can screw up
in some cases, and we know it will. 

So we decided to make sacrifices for the greater good ? :) 

> greg k-h

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