Re: fcntl always fails to delete lock file, and PID is always -6464

From: Daichi GOTO <daichi_at_ongs.co.jp>
Date: Thu, 7 Oct 2010 16:27:03 +0200
On Oct 5, 2010, at 4:52 PM, Garrett Cooper wrote:

> On Tue, Oct 5, 2010 at 1:55 AM, Daichi GOTO <daichi_at_ongs.co.jp> wrote:
>> On Tue, 5 Oct 2010 01:23:02 -0700
>> Garrett Cooper <gcooper_at_FreeBSD.org> wrote:
>>> 2010/10/4 Daichi GOTO <daichi_at_ongs.co.jp>:
>>>> Thanks nice test tool :)  And at last I got it excepting one mystery!
>>>> 
>>>> On Mon, 4 Oct 2010 20:17:08 -0700
>>>> Garrett Cooper <gcooper_at_FreeBSD.org> wrote:
>>>>> Following through the same process on FreeBSD...
>>>>> 
>>>>> Window 1:
>>>>> $ ls -l /tmp/lockfile
>>>>> ls: /tmp/lockfile: No such file or directory
>>>>> $ ./test_fcntl
>>>>> 
>>>>> Window 2:
>>>>> 
>>>>> $ ls -l /tmp/lockfile
>>>>> -rwsr-x---  1 garrcoop  wheel  0 Oct  4 20:14 /tmp/lockfile
>>>>> $ ./test_fcntl
>>>>> test_fcntl: fcntl: Resource temporarily unavailable
>>>> 
>>>> Just my mystery is as follow:
>>>> 
>>>> Windows 1:
>>>> % ./test_fcntl
>>>> My pid: 43490
>>>> 
>>>> Windows 2:
>>>> % ls -l /tmp/lockfile
>>>> -r-sr-x---  1 daichi  wheel  0 10月  5 15:02 /tmp/lockfile    <--- is it weird, isn't it?
>>>> % ./test_fcntl
>>>> test_fcntl: open: Permission denied
>>>> %
>>>> 
>>>> Oops... What's wrong... /tmp is as follow:
>>>> 
>>>> % mount | grep tmp
>>>> /dev/ada0s1f on /tmp (ufs, local, noatime, soft-updates)
>>>> % dumpfs /tmp | grep journal
>>>> flags   soft-updates+journal
>>>> %
>>>> 
>>>> And working scene:
>>>> 
>>>> Windows 2:
>>>> % chmod u+w /tmp/lockfile
>>>> % ls -l /tmp/lockfile
>>>> -rwsr-x---  1 daichi  wheel  0 10月  5 15:22 /tmp/lockfile
>>>> % ./test_fcntl
>>>> My pid: 43646
>>>> test_fcntl: fcntl[1]: Resource temporarily unavailable
>>>> PID=43490 has the lock
>>>> %
>>> 
>>> What's your umask and what are the permissions on /tmp?
>> 
>> % ll / | grep tmp
>> drwxrwxrwt  14 root  wheel      1024 10月  5 17:19 tmp
>> % umask
>> 022
>> % rm -f test
>> % touch test
>> % ll | grep test
>> -rw-r--r--   1 daichi  wheel     0 10月  5 17:52 test
>> %
> 
>    The permissions look ok from my perspective, but the umask is
> different, so you might want to try my umask to make sure that your
> results match mine (and we need to check the requirements to determine
> whether or not the behavior for FreeBSD's umask syscall is correct):
> 
> $ ls -la /tmp/ | head -n 2
> total 462686
> drwxrwxrwt  51 root     wheel         11776 Oct  5 03:11 .
> $ umask
> 0022

The results are different on some users, even on the same user!
(022 and 0022 shows the same results.)

test user:

$ rm -f /tmp/lockfile
$ ./test_fcntl
My pid: 63133
^C
$ ll /tmp/lockfile
---sr-----  1 test  wheel  - 0 Oct  7 23:16 /tmp/lockfile*
$

daichi:
% rm -f /tmp/lockfile     
% ./test_fcntl 
My pid: 63140
^C
% ll /tmp/lockfile
---Sr-x---  1 daichi  wheel  0 10月  7 23:17 /tmp/lockfile
% 

But above daichi's result was ---sr----- as the same as test user.
After some operation, it turns into returing ---Sr-x---. I didn't remember 
what operation did that.

root:
# rm -f /tmp/lockfile
# ./test_fcntl
My pid: 63147
^C
# ls -l /tmp/lockfile
--wSr-S---  1 root  wheel  0 Oct  7 23:20 /tmp/lockfile
# 

It is mystery.

>    Where and how is /tmp mounted (is it a real partition, what
> filesystem, etc)?

UFS+SUJ+noatime real pertition. I checked atime version, and got the same 
result.

>    BTW, when I change my umask to match your's I don't get the same
> results you do on my home machine:
> 
> Window 1:
> 
> $ umask 022
> $ ./test_fcntl
> My pid: 17353
> 
> Window 2:
> 
> $ ./test_fcntl
> My pid: 17356
> test_fcntl: fcntl[1]: Resource temporarily unavailable
> PID=17353 has the lock
> $ ls -l /tmp/lockfile
> -rwSr-----  1 gcooper  wheel  0 Oct  5 07:49 /tmp/lockfile
> 
>    Just to note, the tests before were run on the RHEL 4.8 box with
> the following info, and the FreeBSD box with the following info:
> 
> Red Hat Enterprise Linux AS release 4 (Nahant Update 8)
> Linux sjc-lds-102 2.6.9-89.0.11.ELsmp #1 SMP Mon Aug 31 11:00:34 EDT
> 2009 x86_64 x86_64 x86_64 GNU/Linux
> 
> FreeBSD bioshock.cisco.com 9.0-CURRENT FreeBSD 9.0-CURRENT #1
> r211767M: Sat Aug 28 00:28:45 PDT 2010
> garrcoop_at_bioshock.cisco.com:/usr/obj/usr/src/sys/BIOSHOCK  amd64
> 
>    The tests above were run on a FreeBSD box with the following info:
> 
> FreeBSD bayonetta.local 9.0-CURRENT FreeBSD 9.0-CURRENT #9 r211309M:
> Thu Aug 19 22:50:36 PDT 2010
> root_at_bayonetta.local:/usr/obj/usr/src/sys/BAYONETTA  amd64
> 
>    On bayonetta /tmp is SUJ backed (probably should change that
> though), and on bioshock it's not SUJ backed.
> Thanks!
> -Garrett

Still now, I couldn't find the cause of this issue, but it's ok by code following,
and program should set permission at creating time I guess.

      fd = open("/tmp/lockfile", O_CREAT|O_WRONLY,0600);

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Received on Thu Oct 07 2010 - 12:27:09 UTC

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