linux-kernel - Re: [patch 2/2] Documentation/process: Add tip tree handbook

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Date:   Thu, 8 Nov 2018 12:05:08 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, John Stultz <john.stultz@...aro.org>,
        acme@...hat.com, frederic@...nel.org,
        Jonathan Corbet <corbet@....net>,
        Andy Lutomirski <luto@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Mark Brown <broonie@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [patch 2/2] Documentation/process: Add tip tree handbook

On Thu, Nov 08, 2018 at 08:58:32PM +0100, Thomas Gleixner wrote:
> On Thu, 8 Nov 2018, Paul E. McKenney wrote:
> > On Thu, Nov 08, 2018 at 09:19:33AM -0800, Dan Williams wrote:
> > > On Thu, Nov 8, 2018 at 1:13 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > > >
> > > > On Thu, Nov 08, 2018 at 08:40:12AM +0100, Ingo Molnar wrote:
> > > > > > + - Cc: ``cc-ed-person <person@...l>``
> > > > > > +
> > > > > > +   If the patch should be backported to stable, then please add a '``Cc:
> > > > > > +   stable@...r.kernel.org``' tag, but do not Cc stable when sending your
> > > > > > +   mail.
> > > > >
> > > > > Can I suggest a more canonical form:
> > > > >
> > > > >       Cc: <stable@...r.kernel.org> # v4.18 and later kernels
> > > > >
> > > > > It would be nice if people adding Cc: stable lines would actually try to
> > > > > figure out which exact kernel versions are affected.
> > > 
> > > I know at least StGit mail does not grok that "#"notation. I've
> > > stopped using it in favor of a "Fixes:" tag. I would think "Fixes:" is
> > > preferred over "# <KVER>" if only because it can be used to track
> > > fixes to commits that have been backported to stable. Is there any
> > > reason for "# <KVER>" to continue in a world where we have "Fixes:"?
> > 
> > I sometimes have fixes that need to be different for different past
> > releases.  And there have been cases where RCU patches would apply and
> > build cleanly against releases for which it was not appropriate, but
> > would have some low-probability failure.  Which meant that it could be
> > expected to pass light testing.  :-/
> > 
> > So I sometimes need a way of saying which versions a given patch applies
> > to, independent of the version into which the bug was introduced.
> 
> I can understand that you want to limit the scope of automatic backports.
> 
> But we really should try to always use of the Fixes: tag. In most cases the
> SHA1 of the commit in the fixes tag defines the backport scope. 
> 
> For the rare cases where the buggy commit is really old, but you want to
> limit the backport scope for a reason then I really like to avoid to
> overload the Cc stable tag and have a dedicated tag instead. Something
> like:
> 
>     Fixes: 1234567890AB ("subsys/comp: Short summary")
>     Backport-to: 4.14
> 
> and have that backport tag right under the Fixes tag. If the Backport-to
> tag is ommitted, the SHA1 defines the scope, but I'm fine with making it
> mandatory.
> 
> If there is really the special RCU case where each and every stable version
> needs some special treatment then say:
> 
>     Backport-to: Manual
> 
> or whatever sensible word would express it correctly.
> 
> The Fixes tag is really valuable when you need to make connections and I
> know that the people who are looking into safety-critical Linux value the
> tag because it can be used for tracking and for metrics.

Indeed, I do need to get my act together with the Fixes tag.  And I am
happy with whatever format would limit backports appropriately.

							Thanx, Paul