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Date:	Tue, 10 Nov 2009 11:37:47 -0800
From:	Greg KH <gregkh@...e.de>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC] new -stable tag variant, Git workflow question

On Tue, Nov 10, 2009 at 09:29:48AM -0500, James Bottomley wrote:
> On Mon, 2009-11-09 at 20:14 -0800, Greg KH wrote:
> > On Tue, Nov 10, 2009 at 04:48:31AM +0100, Ingo Molnar wrote:
> > > FYI, today i committed a scheduler performance fix that has a number of 
> > > commit prerequisites for -stable integration. Those commits are not 
> > > marked -stable.
> > > 
> > > Previously, in similar situations, i solved it by email-forwarding the 
> > > prereq commits to stable@...nel.org. (or by waiting for your 'it does 
> > > not apply to -stable' email and figuring out the prereqs then.)
> > > 
> > > But we can move this into the Git commit space too, and minimize the 
> > > work for the -stable team, via a new -stable tag variant. So with this 
> > > new commit i started using a new tagging scheme in the commit itself:
> > > 
> > >  Cc: <stable@...nel.org> # .32.x: a1f84a3: sched: Check for an idle shared cache
> > >  Cc: <stable@...nel.org> # .32.x: 1b9508f: sched: Rate-limit newidle
> > >  Cc: <stable@...nel.org> # .32.x: fd21073: sched: Fix affinity logic
> > >  Cc: <stable@...nel.org> # .32.x
> > >  LKML-Reference: <1257821402.5648.17.camel@...ge.simson.net>
> > >  Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > > 
> > > The tag sequence has the meaning of:
> > > 
> > >   git cherry-pick a1f84a3
> > >   git cherry-pick 1b9508f
> > >   git cherry-pick fd21073
> > >   git cherry-pick <this commit>
> > > 
> > > and i'm wondering whether this tagging scheme is fine with your -stable 
> > > scripting, etc.
> > 
> > It would work just fine.
> > 
> > I only rely on one main script right now, one that runs from James's
> > directory on kernel.org that picks out the "Cc: <stable@...nel.org>"
> > lines and forwards the full commit message to stable@...nel.org.
> > 
> > Then I have a simple script that I just pass the git commit id and
> > formats it properly for inclusion on the quilt tree for the stable
> > queue.  If you list the other git commit ids that are needed as a
> > prerequesite as you did above, that's trivial to also pick out.
> > 
> > So I think this is good for me and my workflow.
> 
> So I take this to mean that I don't alter my script and you pick out the
> precursors with yours ...

Exactly, it's easier for me that way, as I know the dependancy of what
needs to go before what.  And it's just so trivial to feed a git commit
id to my script :)

> > > A further question is, i can see using this tagging scheme in the future 
> > > in merge commits log messages too - will your scripts notice that too?
> > 
> > Hm, I don't think we look at merges as there's nothing there to actually
> > commit.
> > 
> > > For example if there's a few commits left in tip:*/urgent branches 
> > > (tip:sched/urgent, tip:core/urgent, tip:x86/urgent, etc.) by the time 
> > > v2.6.32 is released, i will then merge them into tip:sched/core, 
> > > tip:core/core, tip:x86/core, etc. - and i could use the merge commit as 
> > > a notification area to 'activate' them for -stable backporting via a 
> > > merge commit.
> > > 
> > > This is how such merge commits would look like:
> > > 
> > >   Merge branch 'core/urgent' into core/rcu
> > > 
> > >   Merge reason: Pick up urgent fixes that did not make it into .32.0
> > > 
> > >   Cc: <stable@...nel.org> # .32.x: 83f5b01: rcu: Fix long-grace-period race
> > >   Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > > 
> > > This is not so rare of a situation as it might seem - for the trees i 
> > > maintain it happens in almost every release cycle - i typically skip 
> > > urgent branch merges after -rc8/-rc9, unless they are very-very-urgent 
> > > fixes - but they'd still be eligible for -stable.
> > 
> > Ok, that would be good and fine with me.
> > 
> > James, would your script pick this up, or does it need to also pay
> > attention to merge commits?
> 
> No ... because merge commits should effectively be empty (and when
> they're not you can't generate an applyable diff).  If I understand the
> workflow, the desire is to have the whole branch sent to stable by
> tagging the merge commit.  That's possible ... it's exactly the same
> logic I use in the commit scripts for the SCSI tree, so it should be
> possible to extract the logic.
> 
> By the looks of the above it's only a few commits, or is it the entire
> branch?

I'm thinking the commit would be the merge, right Ingo?  So it would
just be a single commit that has the marker in it.

> > > I've attached the full commit below. The prereq commits are not uptream 
> > > yet, and they dont carry a -stable backporting tag as the -stable 
> > > relevance was not anticipated at that point yet. They will all be 
> > > upstream in the next merge window when Linus merges the relevant tree - 
> > > and then all these tags become visible to the -stable team's scripts.
> > > 
> > > What do you think about this new -stable tagging variant? To me it looks 
> > > quite intuitive, less error-prone and it is more informative as well. 
> > > Furthermore, it gives us some freedom to mark commits as backport 
> > > candidates later on. I kept them oneliners for the purpose of making 
> > > them all self-sufficient tags.
> > 
> > I agree.
> > 
> > > ( Sidenote: i wouldnt go as far as to generate null Git commits to mark
> > >   backports after the fact - this scheme is for a series of commits that 
> > >   get 'completed' - there's usually a final followup commit that can 
> > >   embedd this information. )
> > 
> > That's fine, don't worry about this.
> 
> The question is, how important is this?
> 
> One of the assumptions behind the current setup is that I assume
> backports are independent (so the order of transmission doesn't matter
> that much).  This isn't always true, but the exceptions tend to get
> handled manually.  Part of what the above is requesting is an
> implementation that starts to care about ordering.

No, I'll take care of the ordering myself.  Heck, I already have to do
that today with our current setup as we have dependant staging patches
right now.  I just want to make sure the merge commits will get picked
up and sent to me so I can then pick the correct git commit ids out of
them.

thanks,

greg k-h
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