My kernel hangs again: Help with git please

My kernel hangs again: Help with git please

[Carlo Wood]

Somewhere between 2.6.18 and 2.6.19, a patch was added to the
kernel that makes it hang on my machine after the message:

apgart: Detected an Intel 965G Chipset.

When I upgraded to 2.6.22-rc4 (from debian trunk), I still ran
into this same bug.

After installing git for the first time, I made my first
little steps with git - but it didn't get any further then
an attempt to mount my root because I had done my configuration
wrong (due the fact that libata seems to have moved).

Later, I managed to get the configuration right, compiled
HEAD (I think) and got a working 2.6.22-rc4 (+ patches).
I was very happy, and assumed that by coincidence the very
bug that was introduced shortly after 2.6.18 that made my
machine hang during boot, was fixed only two or so days
after I joined linux-kernel and installed git, somewhere
after 2.6.22-rc4 ... What a coincidence right?

Indeed, I thought it was a bit TOO much of a coincidence.
So I just HAD to see that patch that fixed the problem,
and I tried to used git bisect to find the patch that changes
the behaviour from a hang to a working kernel (that I am
now using to write this very mail).

Surprise: Nothing I try produces a working kernel anymore?!

Therefore I have the following questions:

1) What git command will ASSURE that I get the LATEST
   kernel tree checked out?
 
I tried this:

hikaru:/usr/src/kernel/git/linux-2.6>git branch -l
* bisect
  master
  origin
hikaru:/usr/src/kernel/git/linux-2.6>git reset --hard HEAD
hikaru:/usr/src/kernel/git/linux-2.6>git rev-list --max-count=1 bisect
c420bc9f09a0926b708c3edb27eacba434a4f4ba

And, assuming I have c420bc9f09a0926b708c3edb27eacba434a4f4ba at that
moment, then git reset --hard HEAD didn't do what I wanted: that is
namely -rc3 even! I can see THAT in the Makefile -- but whenever I
see -rc4 in the Makefile, that doesn't garantee in any way (apparently)
that I have the latest of the latest.

2) Is there some way to find back the exact version (git id)
from the .config, System.map and vmlinuz image (or /proc, since I can
boot it)? Because that is all I have left from the time that I managed
to create a working kernel :(

-- 
Carlo Wood <carlo@alinoe.com>

Re: My kernel hangs again: Help with git please

[Daniel Barkalow]

On Sat, 16 Jun 2007, Carlo Wood wrote:

> Therefore I have the following questions:
> 
> 1) What git command will ASSURE that I get the LATEST
>    kernel tree checked out?
>
> I tried this:
> 
> hikaru:/usr/src/kernel/git/linux-2.6>git branch -l
> * bisect
>   master
>   origin
> hikaru:/usr/src/kernel/git/linux-2.6>git reset --hard HEAD

HEAD doesn't mean what you think it means. It's the latest revision on the 
branch with the *. What you want is:

$ git checkout master

This will move the * to "master", which shouldn't have been affected by 
any of this, and move your working directory to this point as well. At 
that point, you should be able to build a working kernel.

What "git reset --hard HEAD" does is discard any differences to tracked 
files between your working directory and the revision you're on. It's 
relevant if you want to discard local changes, not otherwise.

	-Daniel
*This .sig left intentionally blank*

Re: My kernel hangs again: Help with git please

[Carlo Wood]

On Fri, Jun 15, 2007 at 08:33:38PM -0400, Daniel Barkalow wrote:
> HEAD doesn't mean what you think it means. It's the latest revision on the 
> branch with the *. What you want is:
> 
> $ git checkout master
> 
> This will move the * to "master", which shouldn't have been affected by 
> any of this, and move your working directory to this point as well. At 
> that point, you should be able to build a working kernel.
> 
> What "git reset --hard HEAD" does is discard any differences to tracked 
> files between your working directory and the revision you're on. It's 
> relevant if you want to discard local changes, not otherwise.

I don't understand - any branch that I am on has many tags. I can use
'git reset --hard sometag' to change the source tree to that tag (which
works if I look at the version in the Makefile and pick tags that are
far apart enough). Then, shouldn't 'HEAD' have the meaning: the newest
tag on the branch? I was on the 'bisect' branch - but that is a copy
of the master, no? At least, that was what I started on when I started
the bisect.

Anyway, I tried this:

$ git checkout master
$ git branch
  bisect
* master
  origin
$ BRANCH=$(git branch | grep "^\*" | sed -e "s/\* //")
$ echo $BRANCH
master
$ git rev-list --max-count=1 $BRANCH
5ecd3100e695228ac5e0ce0e325e252c0f11806f

Is it correct that this last command gives me the 'git id' (if that
is the correct name for the hash) of the revision that my local
working copy is at?

Can you tell me what is the latest git id that you see?

Because, if I compile 5ecd3100e695228ac5e0ce0e325e252c0f11806f is
still hangs at boot :(

I really don't know how I got a working kernel before :/

-- 
Carlo Wood <carlo@alinoe.com>

Re: My kernel hangs again: Help with git please

[Daniel Barkalow]

On Sat, 16 Jun 2007, Carlo Wood wrote:

> I don't understand - any branch that I am on has many tags. I can use
> 'git reset --hard sometag' to change the source tree to that tag (which
> works if I look at the version in the Makefile and pick tags that are
> far apart enough).

That's not actually the right image. There's a graph of commits with a lot 
of splitting and joining lines. Each branch and each tag sits something in 
this web. The difference between branches and tags is that you're expected 
to move branch pointers around, and tags stay mostly in place. There's no 
accounting of commits newer than the current spot in the web for a branch 
belonging to that branch, so if you move a branch back to an older tag (or 
other commit), the spot it's leaving is no longer "on the branch".

So master is a point in the web, and bisect jumps around through the web 
according to some special rules (due to having git-bisect use the good/bad 
marks do determine which commit to try next, and jump there). git-bisect 
doesn't really even care that you started on any single branch. It's just 
operating on the web, and the branch you start on is treated as an 
arbitrary commit that has the problem.

You may find "gitk --all" informative.

> Anyway, I tried this:
> 
> $ git checkout master
> $ git branch
>   bisect
> * master
>   origin
> $ BRANCH=$(git branch | grep "^\*" | sed -e "s/\* //")
> $ echo $BRANCH
> master
> $ git rev-list --max-count=1 $BRANCH
> 5ecd3100e695228ac5e0ce0e325e252c0f11806f
> 
> Is it correct that this last command gives me the 'git id' (if that
> is the correct name for the hash) of the revision that my local
> working copy is at?

Yes.

> Can you tell me what is the latest git id that you see?

I'm seeing de7f928ca460005086a8296be07c217aac4b625d, but I just got the 
latest code, more recently than you probably did.

> Because, if I compile 5ecd3100e695228ac5e0ce0e325e252c0f11806f is
> still hangs at boot :(

It looks like you moved master back to 2.6.22-rc4 (with git reset --hard 
v2.6.22-rc4) at some point.

What you should do now is:

$ git checkout master
$ git merge origin

Which should move master forward through the web to "origin", which is 
(unless you've moved it) what you got from upsteam.

Alternatively:

$ git checkout master
$ git pull

Should fetch the latest stuff and advance master to the fetched version.

	-Daniel
*This .sig left intentionally blank*

Re: My kernel hangs again: Help with git please

[Carlo Wood]

On Sat, Jun 16, 2007 at 01:28:13AM -0400, Daniel Barkalow wrote:
> That's not actually the right image. There's a graph of commits with a lot 
> of splitting and joining lines. Each branch and each tag sits something in 
> this web. The difference between branches and tags is that you're expected 
> to move branch pointers around, and tags stay mostly in place. There's no 
> accounting of commits newer than the current spot in the web for a branch 
> belonging to that branch, so if you move a branch back to an older tag (or 
> other commit), the spot it's leaving is no longer "on the branch".

Okay, it took me two hours before I understood this... but here's the
picture that I have in mind now:

	   master->X        (merge point)
		  /|
		 / |
      ^ branch->3  X
 Time |         |  |
      |         2  X
		|  |
	        1  X
		|  |
		 \ |
		  \|
		   X        (branch point)
		   |

Then if I define a branch pointer to point to '3', then the branch is
3--2--1. If next I move the branch pointer to point to '2', node '3' is
no longer on the branch because now the branch exists of 2--1, and
HEAD moves to '2' as well.

This seems to make most sense in the light of your last sentence.
I don't understand how I'd have moved branch pointers however. I thought
I would just change my working copy along the branch by specifying
tag nodes. Ie, I have a branch '3'(--2--1) and I say: give me '2',
then give me '1' - and when I do: git reset --hard HEAD - it moves
me to 3 because the branch was never touched.

> So master is a point in the web, and bisect jumps around through the web 
> according to some special rules (due to having git-bisect use the good/bad 
> marks do determine which commit to try next, and jump there). git-bisect 
> doesn't really even care that you started on any single branch. It's just 
> operating on the web, and the branch you start on is treated as an 
> arbitrary commit that has the problem.

Ok - so it does something magical that I don't have to understand :P
The only thing that matters is that I choose the begin and end point,
the first two points, correctly: where one is bad and the other is good.
I seems that git bisect can't deal with swapping good/bad (the 'bad'
one always has to be the newest revision), so I had decided to call
'kernel hangs' good and 'kernel works' bad. The problem then is that
I can't find any starting point anymore that is 'bad'.

> You may find "gitk --all" informative.

The dates on the right side seem to make no sense. Even in a part
where there are no branches/merges at all, the date goes in both
direction (sometimes older, sometimes newer). Roughly it seems that
the newest date is at the top - but I see a lot of times things like:

|||O||  Description   Author1  2007-05-14 03:43:20
|||O||  Description   Author2  2007-05-15 15:10:34
|||O||  Description   Author3  2007-05-13 17:50:27

Thus, there seems to be no time related ordering :/

> It looks like you moved master back to 2.6.22-rc4 (with git reset --hard 
> v2.6.22-rc4) at some point.

Yup, I can see that in the gitk --all graph :)

> What you should do now is:
> 
> $ git checkout master
> $ git merge origin
> 
> Which should move master forward through the web to "origin", which is 
> (unless you've moved it) what you got from upsteam.

$ git merge origin
fatal: Needed a single revision
Usage: /usr/bin/git-merge [-n] [--no-commit] [--squash] [-s <strategy>]... <merge-message> <head> <remote>+

For some reason I don't think I should be needing commands that need
"<merge-message>"; I don't want to change the (local) tree in anyway.

Isn't there another way to just move master back to the HEAD of origin?

> Alternatively:
> 
> $ git checkout master
> $ git pull
> 
> Should fetch the latest stuff and advance master to the fetched version.

I'd rather first reproduce a working kernel - that should be possible
without pulling in more commits.

-- 
Carlo Wood <carlo@alinoe.com>

Re: My kernel hangs again: Help with git please

[Daniel Barkalow]

On Sat, 16 Jun 2007, Carlo Wood wrote:

> On Sat, Jun 16, 2007 at 01:28:13AM -0400, Daniel Barkalow wrote:
> > That's not actually the right image. There's a graph of commits with a lot 
> > of splitting and joining lines. Each branch and each tag sits something in 
> > this web. The difference between branches and tags is that you're expected 
> > to move branch pointers around, and tags stay mostly in place. There's no 
> > accounting of commits newer than the current spot in the web for a branch 
> > belonging to that branch, so if you move a branch back to an older tag (or 
> > other commit), the spot it's leaving is no longer "on the branch".
> 
> Okay, it took me two hours before I understood this... but here's the
> picture that I have in mind now:
> 
> 	     master->X        (merge point)
> 		    /|
> 		   / |
>       ^ branch->3  X
>  Time |         |  |
>       |         2  X
> 		  |  |
> 	          1  X
> 		  |  |
> 		   \ |
> 		    \|
> 		     X        (branch point)
> 		     |

Right, except that, in your repository, "master" has ended up pointing to 
"3" also. Or, in any case, all of your local branches ("master" is no 
different from other branches, except that it's the initial default name 
for a branch) are somewhere down the web from the latest stuff from 
Linus's repositry.

> Then if I define a branch pointer to point to '3', then the branch is
> 3--2--1. If next I move the branch pointer to point to '2', node '3' is
> no longer on the branch because now the branch exists of 2--1, and
> HEAD moves to '2' as well.

Right, except that "HEAD" is really just a symlink, not a pointer 
directly to the history; the branch it points to is what you've got in 
your working directory currently. So in that case, HEAD moves to '2' 
simply because it's indirection for branch, which has moved to 2.

Side note: in more recent versions of git, there's the feature that you 
seem to be trying to use. It's called "detatched HEAD", and means that you 
can have HEAD be some arbitrary commit, not a link to a branch. You'd do 
this with "git checkout <some revision>", and then your working directory 
would match that revision, and "git branch" would have no *, and you 
wouldn't have a current branch at all, and you wouldn't be moving branch 
pointers around. But I don't think you're using a version of git that 
supports this, and you need to get your branch pointers back to the 
present anyway.

> This seems to make most sense in the light of your last sentence.
> I don't understand how I'd have moved branch pointers however. I thought
> I would just change my working copy along the branch by specifying
> tag nodes. Ie, I have a branch '3'(--2--1) and I say: give me '2',
> then give me '1' - and when I do: git reset --hard HEAD - it moves
> me to 3 because the branch was never touched.

git reset --hard <revision> moves the current branch to that revision, as 
well as moving the working directory (and the index, which doesn't matter 
for your case). If you were thinking that it only changed the working 
directory, you probably moved some branches without realizing it.

> > So master is a point in the web, and bisect jumps around through the web 
> > according to some special rules (due to having git-bisect use the good/bad 
> > marks do determine which commit to try next, and jump there). git-bisect 
> > doesn't really even care that you started on any single branch. It's just 
> > operating on the web, and the branch you start on is treated as an 
> > arbitrary commit that has the problem.
> 
> Ok - so it does something magical that I don't have to understand :P
> The only thing that matters is that I choose the begin and end point,
> the first two points, correctly: where one is bad and the other is good.
> I seems that git bisect can't deal with swapping good/bad (the 'bad'
> one always has to be the newest revision), so I had decided to call
> 'kernel hangs' good and 'kernel works' bad. The problem then is that
> I can't find any starting point anymore that is 'bad'.

Right; since the normal goal is to find regressions, not fixes, "bad" is 
the "after it changed" case, and "good" is the "before it changed". It is 
trying to find a commit which all of the "bad" commits are descended from, 
and which is descended from only "good" commits.

> > You may find "gitk --all" informative.
> 
> The dates on the right side seem to make no sense. Even in a part
> where there are no branches/merges at all, the date goes in both
> direction (sometimes older, sometimes newer). Roughly it seems that
> the newest date is at the top - but I see a lot of times things like:
> 
> |||O||  Description   Author1  2007-05-14 03:43:20
> |||O||  Description   Author2  2007-05-15 15:10:34
> |||O||  Description   Author3  2007-05-13 17:50:27
> 
> Thus, there seems to be no time related ordering :/

Those dates are when the patches which became the commits were written. 
The ordering is the lineage of the revisions in the repository. 
Additionally, people's clocks can be wrong, and people may be in different 
time zones (I'm not sure whether gitk shows the author's time zone or your 
time zone; both pieces of information are available, and both can be 
interesting). In any case, the choice of which date to show is to provide 
information that's not implied by the ordering of the items.

What the ordering of items tells you is that, if you check out that middle 
commit, and they're all on the same line, the change in the bottom commit 
will be represented and the change in the top commit won't; in the 
perspective on the project's history encoded in the repository, the middle 
change was applied on top of the bootm one, and the top one was applied on 
top of that. (Even though we know the authors of those changes were 
working independantly, probably based on some older revision)

> > What you should do now is:
> > 
> > $ git checkout master
> > $ git merge origin
> > 
> > Which should move master forward through the web to "origin", which is 
> > (unless you've moved it) what you got from upsteam.
> 
> $ git merge origin
> fatal: Needed a single revision
> Usage: /usr/bin/git-merge [-n] [--no-commit] [--squash] [-s <strategy>]... <merge-message> <head> <remote>+
> 
> For some reason I don't think I should be needing commands that need
> "<merge-message>"; I don't want to change the (local) tree in anyway.
> 
> Isn't there another way to just move master back to the HEAD of origin?

Ah, the syntax of git-merge changed at some point. Try, instead, the less 
intuitive "git pull . origin". Or "git reset --hard refs/heads/origin" or 
maybe "git reset --hard refs/remotes/origin/master".

When you merge something in git, if the other side is a descendant of your 
current point, it just moves your current point to the point the other 
side is at, and doesn't use the message. This is called a "fast-forward 
merge", because it makes your branch be at a point descended from both the 
old value of your branch and the other side (that being the important 
feature of a "merge"), but it does it without creating anything new, 
because an existing commit was sufficient. So, if you expect that you're 
moving strictly forward in history, you can do this by asking for a merge. 
(But the program called "git merge" in the version you have actually 
doesn't do fast-forwards, sort of confusingly; in later versions, things 
have been rearranged somewhat. In your version, you have to ask to pull in 
changes from your own copy of the repository in order to trigger the 
fast-forward logic.)

> > Alternatively:
> > 
> > $ git checkout master
> > $ git pull
> > 
> > Should fetch the latest stuff and advance master to the fetched version.
> 
> I'd rather first reproduce a working kernel - that should be possible
> without pulling in more commits.

Sure. Hopefully, newer things haven't broken anything else (or the same 
thing again), but it's good to get everything sane first. But if you find 
you've lost all trace of what you'd gotten (if "origin" also got moved, 
for example), you can just get the latest mainline. There's also "git 
lost+found" which can recover bits of history that have been completely 
lost from your local repository, but that's probably more trouble than 
it's worth.

	-Daniel
*This .sig left intentionally blank*

Re: My kernel hangs again: Help with git please

[Alex Riesen]

Carlo Wood, Sat, Jun 16, 2007 16:03:40 +0200:
> $ git merge origin
> fatal: Needed a single revision
> Usage: /usr/bin/git-merge [-n] [--no-commit] [--squash] [-s <strategy>]... <merge-message> <head> <remote>+
> 
> For some reason I don't think I should be needing commands that need
> "<merge-message>"; I don't want to change the (local) tree in anyway.

I'd recommend to upgrade your git. There are some really nice
improvements in the latest versions (1.5.2.2, for instance).
Particularly, the command above would have worked. That is, assuming
you actually do have that origin branch. In any case, a

    $ git fetch git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git master
    $ git reset --hard FETCH_HEAD

will get you the very latest kernel in your working directory. Has
some disadvantages, though: does not retrieve the tags and destroys
local changes.

But you'll find a man page of git-remote and git-config very
interesting, especially wrt the above operation. I do just "git pull",
for example and actually _am_ sure I get the latest kernel, get all
the tags and never loose local changes.