GNU bug report logs - #24659
'mkdir' procedure is neither thread-safe nor safe (2.0.12)

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: bug-guile <at> gnu.org
Subject: 'mkdir' procedure is neither thread-safe nor safe (2.0.12)
Date: Mon, 10 Oct 2016 18:39:47 +0200

Hello!

When the optional ‘mode’ argument to the ‘mkdir’ procedure is omitted,
umask(2) is used to find out what the current mask is and to compute the
mode argument to mkdir(2):

--8<---------------cut here---------------start------------->8---
  if (SCM_UNBNDP (mode))
    {
      mask = umask (0);
      umask (mask);
      STRING_SYSCALL (path, c_path, rv = mkdir (c_path, 0777 ^ mask));
    }
--8<---------------cut here---------------end--------------->8---

The problem is that this changes the process’ umask globally for a short
duration, during which other threads will get 0 as the mask…

Furthermore, AFAICS, the above logic is redundant with what the kernel
does anyway.  That is, in a single-threaded program,

  mask = umask (0);
  umask (mask);
  mkdir (file, 0777 ^ mask);

is equivalent to:

  mkdir (file, 0777);

Am I right that we should just remove these two ‘umask’ calls?

Ludo’.

PS: This code has been there since 1996 or earlier.

Message #8 received at submit <at> debbugs.gnu.org (full text, mbox):

From: <tomas <at> tuxteam.de>
To: bug-guile <at> gnu.org
Subject: Re: bug#24659: 'mkdir' procedure is neither thread-safe nor safe
 (2.0.12)
Date: Mon, 10 Oct 2016 20:25:37 +0200

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Mon, Oct 10, 2016 at 06:39:47PM +0200, Ludovic Courtès wrote:
> Hello!

[...]

> Furthermore, AFAICS, the above logic is redundant with what the kernel
> does anyway.  That is, in a single-threaded program,
> 
>   mask = umask (0);
>   umask (mask);
>   mkdir (file, 0777 ^ mask);
> 
> is equivalent to:
> 
>   mkdir (file, 0777);
> 
> Am I right that we should just remove these two ‘umask’ calls?

According to umask(2), yes, you are right. Unless someone has been
trying to work around some platform-specific bug/idiosyncracy.

Regards
- -- t
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Message #13 received at 24659 <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: <tomas <at> tuxteam.de>
Cc: 24659 <at> debbugs.gnu.org
Subject: Re: bug#24659: 'mkdir' procedure is neither thread-safe nor safe
 (2.0.12)
Date: Tue, 11 Oct 2016 11:13:19 +0200

Hi,

<tomas <at> tuxteam.de> skribis:

> On Mon, Oct 10, 2016 at 06:39:47PM +0200, Ludovic Courtès wrote:
>> Hello!
>
> [...]
>
>> Furthermore, AFAICS, the above logic is redundant with what the kernel
>> does anyway.  That is, in a single-threaded program,
>>
>>   mask = umask (0);
>>   umask (mask);
>>   mkdir (file, 0777 ^ mask);
>>
>> is equivalent to:
>>
>>   mkdir (file, 0777);
>>
>> Am I right that we should just remove these two ‘umask’ calls?
>
> According to umask(2), yes, you are right. Unless someone has been
> trying to work around some platform-specific bug/idiosyncracy.

I don’t think there was ever a good reason for this.

Fixed in 245608911698adb3472803856019bdd5670b6614.

Thanks for your feedback,
Ludo’.

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