Git merge checking out impossible commits

[Johannes Wienke]

Hi,

we are using special merge simulator projects for feature branches where
the idea is that the feature branch is automatically merged onto the
master before compiling and testing it so that also the merging behavior
is verified. All of these projects are multi configuration jobs. So far
this worked quite well but since a few days we are noticing a weird
behavior:

In one of the feature branches we did some force pushing and after that
we noticed two error conditions.

1. The coordinator performed the merge successfully, which created a new
revision with hash 5af79d528388216aa25a24c27f0a16d8dc55bdb6. All slaves
of the multi configuration project then try to checkout that revision,
which obviously does not exist in their local repositories. Hence, they
end up with

FATAL: Could not checkout master with start point
5af79d528388216aa25a24c27f0a16d8dc55bdb6
hudson.plugins.git.GitException: Could not checkout master with start
point 5af79d528388216aa25a24c27f0a16d8dc55bdb6
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl$8.execute(CliGitAPIImpl.java:1448)
at
org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler$1.call(RemoteGitImpl.java:153)
at
org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler$1.call(RemoteGitImpl.java:146)
at hudson.remoting.UserRequest.perform(UserRequest.java:118)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:328)
at
hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:701)
Caused by: hudson.plugins.git.GitException: Command "git checkout -f
5af79d528388216aa25a24c27f0a16d8dc55bdb6" returned status code 128:
stdout:
stderr: fatal: reference is not a tree:
5af79d528388216aa25a24c27f0a16d8dc55bdb6

at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:1276)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:1253)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:1249)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommand(CliGitAPIImpl.java:1065)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommand(CliGitAPIImpl.java:1075)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl$8.execute(CliGitAPIImpl.java:1431)
... 11 more

2. After wiping the workspace of that job we ended up in a second error
condition already on the coordinator side:

Merging Revision 5af79d528388216aa25a24c27f0a16d8dc55bdb6 () onto
origin/master using default strategy
FATAL: Could not checkout master with start point
5af79d528388216aa25a24c27f0a16d8dc55bdb6
hudson.plugins.git.GitException: Could not checkout master with start
point 5af79d528388216aa25a24c27f0a16d8dc55bdb6
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl$8.execute(CliGitAPIImpl.java:1448)
at
org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler$1.call(RemoteGitImpl.java:153)
at
org.jenkinsci.plugins.gitclient.RemoteGitImpl$CommandInvocationHandler$1.call(RemoteGitImpl.java:146)
at hudson.remoting.UserRequest.perform(UserRequest.java:118)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:328)
at
hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:701)
Caused by: hudson.plugins.git.GitException: Command "git checkout -f
5af79d528388216aa25a24c27f0a16d8dc55bdb6" returned status code 128:
stdout:
stderr: fatal: reference is not a tree:
5af79d528388216aa25a24c27f0a16d8dc55bdb6

at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:1276)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:1253)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:1249)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommand(CliGitAPIImpl.java:1065)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommand(CliGitAPIImpl.java:1075)
at
org.jenkinsci.plugins.gitclient.CliGitAPIImpl$8.execute(CliGitAPIImpl.java:1431)
... 11 more

It seems that the master cached the last revision (which it generated
locally, so it will never be available after pulling) and refused to
forget about this revision. It must be cached somewhere but we have no
idea how to get rid of this.

Has anyone seen such errors and know about ways to cure this?

Cheers,
Johannes

--
Johannes Wienke, Researcher at CoR-Lab / CITEC, Bielefeld University
Address: Inspiration 1, D-33619 Bielefeld, Germany (Room 1.307)
Phone: +49 521 106-67277