linux-kernel - Re: current git kernel has strange problems during bisect

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Date:	Mon, 12 Jan 2009 01:17:31 +0300
From:	"Alexey Zaytsev" <alexey.zaytsev@...il.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Sam Ravnborg" <sam@...nborg.org>,
	"Christian Borntraeger" <borntraeger@...ibm.com>,
	"Johannes Schindelin" <Johannes.Schindelin@....de>,
	git@...r.kernel.org,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: current git kernel has strange problems during bisect

On Sun, Jan 11, 2009 at 23:04, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
>
> On Sun, 11 Jan 2009, Sam Ravnborg wrote:
>>
>> The cost of moving this piece of history from one git tree to another
>> git tree is that we make it harder to debug the kernel for the advanced user
>> that knows how to do bisect.
>>
>> It is not like this history would be lost - one just had to look
>> somewhere else to find it.
>>
>> That may be a bad pain/benefit ratio - time will tell.
>
> Umm. No.
>
> Time is exactly what makes it useful. It will make all the downsides
> shrink, and the advantages stay.
>
>> There should be a way to avoid such pain when bisecting without
>> having to mark a semi-random (for the average person) commit as good.
>
> Well, you don't actually have to mark that semi-random one as good either.
> What you can do is to just mark anything that _only_ contains fs/btrfs as
> good. IOW, you don't have to know the magic number - you just have to be
> told that "oh, if you only have btrfs files, and you're not actively
> bisecting a btrfs bug, just do 'git bisect good' and continue".
>
> Yeah, you'll hit it a few times, but you don't even have to compile things
> or boot anything, so it's not actually going to be all that much slower
> than just knowing about the magic point either.

But would not such bug avoid being bisected if you blindly
mark btrfs commits as good?

v2.6.29 <-- bad
...
...
...
btrfs stuff <-- mark as good
...
the-real-bug
...
v2.6.28 <-- good

So you hit the btrfs commit, mark it as good, leaving the real bug below,
and the bisection continues, with both sides being actually bad.

Am I missing something?
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