Re: Worktree creation race

> Hello,
>
> I am writing to report a bug. The original report is from my colleague, I am also providing his suggestions.
>
> There is insufficient locking for worktree addition. Adding worktree may fail.
>
> The problem is that git reads the directory entries in $GIT_DIR/worktrees, 
> finds a worktree name that does not exist, tries to create it, and if an 
> error is returned adding the worktree fails. When multiple git processes 
> do this in parallel only one adds a worktree and the others fail. Git should 
> reread the directory and find a new name that does not exist when creating 
> the worktree directory fails because another git process already created it.
>
> I suppose adding PID in the tree name would mitigate the issue to the point it will be very unlikely to encounter.
>
> I need more than the tree in the temporary directory so using the temporary directory directly as a tree is out of question.
>
> to test:
>
> cd /dev/shm
> mkdir gittest
> cd gittest
> git init gitrepo
> cd gitrepo
> git commit --allow-empty -m Empty
> for n in $(seq 10000) ; do ( tmp=$(mktemp -d /dev/shm/gittest/test.XXXXXXXXXXX) ; mkdir $tmp/test ; git worktree add --detach $tmp/test ; ) & done
>
> (you should see many messages like: 
> fatal: could not create directory of '.git/worktrees/test284': File exists)
>
> Greetings,
> Marketa
>
>