open after unlink tries to open old file

open after unlink tries to open old file

[Donald Buczek]

I see this code

     #include <stdlib.h>
     #include <stdio.h>
     #include <sys/types.h>
     #include <sys/stat.h>
     #include <fcntl.h>
     #include <unistd.h>

     #define FILENAME "test.dat"

     int main() {
         int i;
         int fd;
         unlink(FILENAME);
         for  (i=0;i<1000;i++) {
             printf("%d\n",i);
             if ((fd=open(FILENAME,O_WRONLY+O_CREAT,0))==-1) {
                 perror("open");
                 exit(1);
             }
             if (close(fd)==-1) {
                 perror("close");
                 exit(1);
             }
             if (unlink(FILENAME)==-1) {
                 perror("unlink");
                 exit(1);
             }
         }
     }

failing most of the time in NFS-mounted directories:

     buczek@theinternet:~$ uname -a
     Linux theinternet.molgen.mpg.de 4.4.52.mx64.142 #1 SMP Fri Mar 3 
21:25:00 CET 2017 x86_64 GNU/Linux
     buczek@theinternet:~$ nfs_test

     0
     1
     2
     3
     4
     open: Permission denied
     buczek@theinternet:~$

but I fail to find an answer to the question, whether this is supposed 
to work or not. Is this a bug or a caching feature?

Thanks
   Donald

-- 
Donald Buczek
buczek@molgen.mpg.de
Tel: +49 30 8413 1433

Re: open after unlink tries to open old file

[Donald Buczek]

On 03/10/17 14:55, Donald Buczek wrote:
> I see this code
>
>     #include <stdlib.h>
>     #include <stdio.h>
>     #include <sys/types.h>
>     #include <sys/stat.h>
>     #include <fcntl.h>
>     #include <unistd.h>
>
>     #define FILENAME "test.dat"
>
>     int main() {
>         int i;
>         int fd;
>         unlink(FILENAME);
>         for  (i=0;i<1000;i++) {
>             printf("%d\n",i);
>             if ((fd=open(FILENAME,O_WRONLY+O_CREAT,0))==-1) {
>                 perror("open");
>                 exit(1);
>             }
>             if (close(fd)==-1) {
>                 perror("close");
>                 exit(1);
>             }
>             if (unlink(FILENAME)==-1) {
>                 perror("unlink");
>                 exit(1);
>             }
>         }
>     }
>
> failing most of the time in NFS-mounted directories:
>
>     buczek@theinternet:~$ uname -a
>     Linux theinternet.molgen.mpg.de 4.4.52.mx64.142 #1 SMP Fri Mar 3 
> 21:25:00 CET 2017 x86_64 GNU/Linux
>     buczek@theinternet:~$ nfs_test
>
>     0
>     1
>     2
>     3
>     4
>     open: Permission denied
>     buczek@theinternet:~$
>
> but I fail to find an answer to the question, whether this is supposed 
> to work or not. Is this a bug or a caching feature?
>
> Thanks
>   Donald

With some bisect work I discovered, that this was just a different 
manifestation of Bug 109771 [1] reported by myself and fixed by Trond 
[2] for Linux v4.5. Many of my clients are back on Linux v4.4 longterm 
because of unrelated issues with other releases and I wrongly thought, 
the fix was backported.

Donald


[1] https://bugzilla.kernel.org/show_bug.cgi?id=109771
[2] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=762674f

-- 
Donald Buczek
buczek@molgen.mpg.de
Tel: +49 30 8413 1433