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Re: [PATCH 2/2] setup: don't fail if commondir reference is deleted.

From
PWPhillip Wood <phillip.wood@talktalk.net>
Date
Feb 21, 2019, 17:07 UTC
Message-ID
<adc0f7f9-aa41-780e-6fce-94d493fac318@talktalk.net>
In-Reply-To
<20190221145056.53b98b2a@kitsune.suse.cz>
Hi Michal/Duy
On 21/02/2019 13:50, Michal Suchánek wrote:
Show 24 quoted lines
> On Thu, 21 Feb 2019 17:50:38 +0700
> Duy Nguyen <pclouds@gmail.com> wrote:
> 
>> On Tue, Feb 19, 2019 at 12:05 AM Michal Suchanek <msuchanek@suse.de> wrote:
>>>
>>> When adding wotktrees git can die in get_common_dir_noenv while
>>> examining existing worktrees because the commondir file does not exist.
>>> Rather than testing if the file exists before reading it handle ENOENT.
>>
>> I don't think we could go around fixing every access to incomplete
>> worktrees like this. If this is because of racy 'worktree add', then
>> perhaps a better solution is make it absolutely clear it's not ready
>> for anybody to access.
>>
>> For example, we can suffix the worktree directory name with ".lock"
>> and make sure get_worktrees() ignores entries ending with ".lock".
>> That should protect other commands while 'worktree add' is still
>> running. Only when the worktree is complete that 'worktree add' should
>> rename the directory to lose ".lock" and run external commands like
>> git-checkout to populate the worktree.
> 
> The problem is we don't forbid worktree names ending with ".lock".
> Which means that if we start to forbid them now existing worktrees
> might become inaccessible.

I think it is also racy as the renaming breaks the use of mkdir erroring out if the directory already exists. One solution is to have a lock entry in $GIT_COMMON_DIR/worktree-locks and make sure the code that iterates over the entries in $GIT_COMMON_DIR/worktrees skips any that have a corresponding ignores in $GIT_COMMON_DIR/worktree-locks. If the worktree-locks/<dir> is created before worktree/<dir> then it should be race free (you will have to remove the lock if the real entry cannot be created and then increment the counter and try again). Entries could also be locked on removal to prevent a race there.

Best Wishes
Phillip
> Thanks
> 
> Michal
>
Previous: Michal SuchánekNext: Eric Sunshine
Message 7 of 27 in “worktree add race fix”
  1. 0/2 worktree add race fixMichal Suchanek, Feb 18, 2019
  2. 1/2 worktree: fix worktree add race.Michal Suchanek, Feb 18, 2019
  3. 2/2 setup: don't fail if commondir reference is deleted.Michal Suchanek, Feb 18, 2019
  4. Eric SunshineFeb 18, 2019
  5. Duy NguyenFeb 21, 2019
  6. Michal SuchánekFeb 21, 2019
  7. Phillip WoodFeb 21, 2019
  8. Eric SunshineFeb 21, 2019
  9. Phillip WoodFeb 21, 2019
  10. Michal SuchánekMar 4, 2019
  11. Michal SuchánekFeb 21, 2019
  12. Duy NguyenFeb 22, 2019
  13. Phillip WoodFeb 22, 2019
  14. Duy NguyenFeb 22, 2019
  15. 1/2 worktree: fix worktree add race.Michal Suchanek, Feb 20, 2019
  16. Eric SunshineFeb 20, 2019
  17. Michal SuchánekFeb 20, 2019
  18. Duy NguyenMar 8, 2019
  19. Eric SunshineMar 8, 2019
  20. Junio C HamanoMar 11, 2019
  21. 2/2 setup: don't fail if commondir reference is deleted.Michal Suchanek, Feb 20, 2019
  22. Eric SunshineFeb 20, 2019
  23. Michal SuchánekFeb 20, 2019
  24. Eric SunshineFeb 20, 2019
  25. Eric SunshineFeb 21, 2019
  26. Michal SuchánekFeb 21, 2019
  27. Michal SuchánekFeb 21, 2019

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