最近需要revert两个commit，其中一个是merge之后生成的commit。非merge的commit顺利revert成功，merge的commit返回错误：
fatal: Commit <SHA1> is a merge but no -m option was given.
http://stackoverflow.com/questions/7099833/how-to-revert-a-merge-commit-thats-already-pushed-to-remote-branch
The -m option specifies the parent number. This is because a merge commit has more than one parent, and Git does not know automatically which parent was the mainline, and which parent was the branch you want to un-merge.
When you view a merge commit in the output of git log, you will see its parents listed on the line that begins with Merge:
commit 8f937c683929b08379097828c8a04350b9b8e183
Merge: 8989ee0 7c6b236
Author: Ben James <ben@example.com>
Date: Wed Aug 17 22:49:41 2011 +0100Merge branch 'gh-pages'Conflicts:README
In this situation, git revert 8f937c6 -m 1 will get you the tree as it was in 8989ee0, and git revert -m 2 will reinstate the tree as it was in 7c6b236.
我这里需要revert到后一个parent，所以具体的命令就是
git revert [SHA1] -m 2