2017-03-10 14:02:52

by Donald Buczek

Subject: open after unlink tries to open old file

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
[email protected]
Tel: +49 30 8413 1433

2017-03-24 15:22:48

by Donald Buczek

Subject: Re: open after unlink tries to open old file

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
[email protected]
Tel: +49 30 8413 1433