git bisect result off by 1 commit

git bisect result off by 1 commit

[Tim Chen]

When I am doing a git bisect to track down a problem commit on the Linux 
kernel tree, I found that git bisect actually led me to a patch that's one
before the problem commit.

In particular,

$ git bisect replay bisectlog 
Previous HEAD position was d54b1a9... perf script: Remove use of die/exit
HEAD is now at a0d271c... Linux 3.6
Bisecting: 0 revisions left to test after this (roughly 0 steps)
[d54b1a9e0eaca92cde678d19bd82b9594ed00450] perf script: Remove use of die/exit

However, the patch that is problematic is the one before the one git bisect indicated.
[commit 8d3eca20b9f31cf10088e283d704f6a71b9a4ee2].

I am running git 1.7.11.7.

Tim


The bisect record is as follow:

------------bisectlog-----------------
git bisect start
# good: [a0d271cbfed1dd50278c6b06bead3d00ba0a88f9] Linux 3.6
git bisect good a0d271cbfed1dd50278c6b06bead3d00ba0a88f9
# bad: [ddffeb8c4d0331609ef2581d84de4d763607bd37] Linux 3.7-rc1
git bisect bad ddffeb8c4d0331609ef2581d84de4d763607bd37
# bad: [24d7b40a60cf19008334bcbcbd98da374d4d9c64] ARM: OMAP2+: PM: MPU DVFS: use generic CPU device for MPU-SS
git bisect bad 24d7b40a60cf19008334bcbcbd98da374d4d9c64
# bad: [d9a807461fc8cc0d6ba589ea0730d139122af012] Merge tag 'usb-3.6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb
git bisect bad d9a807461fc8cc0d6ba589ea0730d139122af012
# bad: [06d2fe153b9b35e57221e35831a26918f462db68] Merge tag 'driver-core-3.6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core
git bisect bad 06d2fe153b9b35e57221e35831a26918f462db68
# bad: [7e92daaefa68e5ef1e1732e45231e73adbb724e7] Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect bad 7e92daaefa68e5ef1e1732e45231e73adbb724e7
# good: [620e77533f29796df7aff861e79bd72e08554ebb] Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect good 620e77533f29796df7aff861e79bd72e08554ebb
# bad: [8ad7013b252ba683055df19e657eb03d98f4f312] perf test: Add round trip test for sw and hw event names
git bisect bad 8ad7013b252ba683055df19e657eb03d98f4f312
# good: [f47b58b75f5e2a424834eb15f7565a7458a12f44] perf symbols: Fix builds with NO_LIBELF set
git bisect good f47b58b75f5e2a424834eb15f7565a7458a12f44
# good: [e1aa7c30c599e99b4544f9e5b4c275c8a5325bdc] tools lib traceevent: Fix strerror_r() use in pevent_strerror
git bisect good e1aa7c30c599e99b4544f9e5b4c275c8a5325bdc
# good: [ff1a70e75fd005821ab5f2211312a8aa13bbf959] tools lib traceevent: Modify header to work in C++ programs
git bisect good ff1a70e75fd005821ab5f2211312a8aa13bbf959
# bad: [4592281403e74dc4401d5803ec9948d43bbee7ae] perf tools: Remove the node from rblist in strlist__remove
git bisect bad 4592281403e74dc4401d5803ec9948d43bbee7ae
# good: [cc58482133296f52873be909a2795f6d934ecec9] perf help: Remove use of die and handle errors
git bisect good cc58482133296f52873be909a2795f6d934ecec9
# bad: [8d3eca20b9f31cf10088e283d704f6a71b9a4ee2] perf record: Remove use of die/exit
git bisect bad 8d3eca20b9f31cf10088e283d704f6a71b9a4ee2

Re: git bisect result off by 1 commit

[Junio C Hamano]

Tim Chen <tim.c.chen@linux.intel.com> writes:

> When I am doing a git bisect to track down a problem commit on the Linux 
> kernel tree, I found that git bisect actually led me to a patch that's one
> before the problem commit.
>
> In particular,
>
> $ git bisect replay bisectlog 
> Previous HEAD position was d54b1a9... perf script: Remove use of die/exit
> HEAD is now at a0d271c... Linux 3.6
> Bisecting: 0 revisions left to test after this (roughly 0 steps)
> [d54b1a9e0eaca92cde678d19bd82b9594ed00450] perf script: Remove use of die/exit
>
> However, the patch that is problematic is the one before the one git bisect indicated.
> [commit 8d3eca20b9f31cf10088e283d704f6a71b9a4ee2].

Looks perfectly normal to me.  The message above:

> HEAD is now at a0d271c... Linux 3.6
> Bisecting: 0 revisions left to test after this (roughly 0 steps)
> [d54b1a9e0eaca92cde678d19bd82b9594ed00450] perf script: Remove use of die/exit

is asking you to test the commit at d54b1a9e and tell it the result
of the test.  The message says "0 left to test *after* this";
doesn't it mean you still need to do *this*?

A bisecct session ends when it tells you

	XXXXXX is the first bad commit

which I do not see in the above.  You seem to have stopped before
that happens.

Re: git bisect result off by 1 commit

[Tim Chen]

> 
> Looks perfectly normal to me.  The message above:
> 
> > HEAD is now at a0d271c... Linux 3.6
> > Bisecting: 0 revisions left to test after this (roughly 0 steps)
> > [d54b1a9e0eaca92cde678d19bd82b9594ed00450] perf script: Remove use of die/exit
> 
> is asking you to test the commit at d54b1a9e and tell it the result
> of the test.  The message says "0 left to test *after* this";
> doesn't it mean you still need to do *this*?
> 
> A bisecct session ends when it tells you
> 
> 	XXXXXX is the first bad commit
> 
> which I do not see in the above.  You seem to have stopped before
> that happens.

Yes, I should do one more step.  Thanks for catching.

Tim