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From: Phillip Wood <phillip.wood@talktalk.net>
To: Duy Nguyen <pclouds@gmail.com>,
	Phillip Wood <phillip.wood@dunelm.org.uk>
Cc: "Michal Suchánek" <msuchanek@suse.de>,
	"Git Mailing List" <git@vger.kernel.org>,
	"Eric Sunshine" <sunshine@sunshineco.com>,
	"Marketa Calabkova" <mcalabkova@suse.cz>,
	"Junio C Hamano" <gitster@pobox.com>
Subject: Re: [PATCH 2/2] setup: don't fail if commondir reference is deleted.
Date: Fri, 22 Feb 2019 10:20:27 +0000	[thread overview]
Message-ID: <1e0e8a07-f310-adc7-0538-c1b738da0e98@talktalk.net> (raw)
In-Reply-To: <CACsJy8B2HRyBKQd+S7hjfU+xGFH+_y0YKcw8397znc2eGUBogQ@mail.gmail.com>

Hi Duy

On 22/02/2019 09:32, Duy Nguyen wrote:
> On Fri, Feb 22, 2019 at 12:07 AM Phillip Wood <phillip.wood@talktalk.net> wrote:
>>
>> Hi Michal/Duy
>>
>> On 21/02/2019 13:50, Michal Suchánek wrote:
>>> 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.
> 
> You mean the part where we see "fred" exists and decide to try the
> name "fred1" instead (i.e. patch 1/2)?
> 
> I don't think it's the problem if that's the case. We mkdir
> "fred.lock" _then_ check if "fred" exists. If it does, remove
> fred.lock and move on to fred1.lock. Then we rename fred1.lock to
> fred1 and error out if rename fails.

Ah you're right, if another process tries to create fred.lock as we're 
renaming it either their mkdir fred.lock will fail or they'll see fred 
once they've made fred.lock

Sorry for the confusion

Phillip

  reply	other threads:[~2019-02-22 10:20 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-18 17:04 [PATCH 0/2] worktree add race fix Michal Suchanek
2019-02-18 17:04 ` [PATCH 1/2] worktree: fix worktree add race Michal Suchanek
2019-02-18 17:04 ` [PATCH 2/2] setup: don't fail if commondir reference is deleted Michal Suchanek
2019-02-18 21:00   ` Eric Sunshine
2019-02-21 10:50   ` Duy Nguyen
2019-02-21 13:50     ` Michal Suchánek
2019-02-21 17:07       ` Phillip Wood
2019-02-21 17:12         ` Eric Sunshine
2019-02-21 17:27           ` Phillip Wood
2019-03-04 13:30             ` Michal Suchánek
2019-02-21 17:33           ` Michal Suchánek
2019-02-22  9:32         ` Duy Nguyen
2019-02-22 10:20           ` Phillip Wood [this message]
2019-02-22  9:26       ` Duy Nguyen
2019-02-20 16:16 ` [PATCH v3 1/2] worktree: fix worktree add race Michal Suchanek
2019-02-20 16:34   ` Eric Sunshine
2019-02-20 17:29     ` Michal Suchánek
2019-03-08  9:20   ` Duy Nguyen
2019-03-08  9:37     ` Eric Sunshine
2019-03-11  1:55     ` Junio C Hamano
2019-02-20 16:16 ` [PATCH v3 2/2] setup: don't fail if commondir reference is deleted Michal Suchanek
2019-02-20 16:55   ` Eric Sunshine
2019-02-20 17:16     ` Michal Suchánek
2019-02-20 18:35       ` Eric Sunshine
2019-02-21  9:27         ` Eric Sunshine
2019-02-21 11:13           ` Michal Suchánek
2019-02-21 11:19         ` Michal Suchánek

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