what to do with “magit-wip-commit-worktree: Cannot read tree refs/heads/master”?

Question

When I commit via magit I get:

magit-wip-commit-worktree: Cannot read tree refs/heads/master

while it commits ok. But the message frightens me. There seems to be nothing wrong with the repo:

$ git fsck
Checking object directories: 100% (256/256), done.
Checking objects: 100% (2270/2270), done.
dangling blob  ff2aef45cae6a3b1f980c192c748af754fb538d4

and there are readable files which match the message:

$ find .git | grep refs/heads/master | xargs ls -l
-rw-r--r-- 1 grfz grfz 12505 Okt 28 13:20 .git/logs/refs/heads/master
-rw-r--r-- 1 grfz grfz   495 Okt 28 13:20 .git/logs/refs/wip/index/refs/heads/master
-rw-r--r-- 1 grfz grfz    41 Okt 28 13:20 .git/refs/heads/master
-rw-r--r-- 1 grfz grfz    41 Okt 28 13:20 .git/refs/wip/index/refs/heads/master

There is nothing special about this repo:

core.excludesfile=/home/grfz/.gitignore_global
core.whitespace=trailing-space,space-before-tab,indent-with-non-tab
sendemail.chainreplyto=false
transfer.fsckobjects=true
fetch.fsckobjects=true
receive.fsckobjects=true
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true

The customizables in cutomize-group magit-wip and magit-wip-legacy are all at standard values.

I used the worlds mightiest search engine and found: nothing besides magit documentation and the like. This astonishes me.

I would at least like to silence this message, better find its root cause.

Answer 1

Update magit, it's a bug which was fixed yesterday: https://github.com/magit/magit/issues/3631.

(I am repeating Noam's comment as an answer because every question needs an answer.)

Answer 2

This can also happen if there's a stale git process. Check ps for stale git processes, and if so end them and remove .git/index.lock