linux-kernel - Re: Kernel panic on Google Pixel devices due to regulator patch

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Message-ID: <20191218161806.GF3219@sirena.org.uk>
Date:   Wed, 18 Dec 2019 16:18:06 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Siddharth Kapoor <ksiddharth@...gle.com>, lee.jones@...aro.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: Kernel panic on Google Pixel devices due to regulator patch

On Wed, Dec 18, 2019 at 03:22:19PM +0100, Greg KH wrote:
> On Wed, Dec 18, 2019 at 01:11:14PM +0000, Mark Brown wrote:
> > On Wed, Dec 18, 2019 at 01:21:57PM +0100, Greg KH wrote:

> > > It is, but it's the latest stable kernel (well close to), and your patch
> > > was tagged by you to be backported to here, so if there's a problem with
> > > a stable branch, I want to know about it as I don't want to see
> > > regressions happen in it.

> > I don't track what's in older stable kernels, it wanted to go back at
> > least one kernel revision but the issue has been around since forever.

> Ok, you can always mark patches that way if you want to :)

That's what a tag to stable with no particular revision attached to it
is isn't it?

> > If you don't want to be messing with timing luck then you probably want
> > to be having a look at what Sasha's bot is doing, it's picking up a lot
> > of things that are *well* into this sort of territory (and the bad
> > interactions with out of tree code territory).  I personally would not
> > be using stable these days if I wasn't prepared to be digging into
> > something like this.

> I watch what his bot is doing, and we have tons of testing happening as
> well, which is reflected by the fact that THIS WAS CAUGHT HERE.  This is

You don't have anywhere near the level of testing that you'd need to
cover what the bot is trying to pull in, the subsystem and driver
coverage is extremely thin relative to the enthusiasm with which things
are being picked up.  All the pushback I see in review is on me for 
being conservative about what gets pulled into stable and worrying about
interactions with out of tree code.

> a sign that things are working, it's just that some SoC trees are slower
> than mainline by a few months, and that's fine.  It's worlds better than
> the SoC trees that are no where close to mainline, and as such, totally
> insecure :)

What you appear to have caught here is an interaction with some
unreviewed vendor code - how much of that is going on in the vendor
trees you're not testing?  If we want to encourage people to pull in
stable we should be paying attention to that sort of stuff.

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