Re: nfsdv4 leaks file descriptors

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Apr 12, 2011 at 04:01:50PM +0200, Gerhard Heift wrote:
> Hello,
> 
> I have a linux kernel (2.6.38.2, armv5tel) running which exports a
> directory with following options:

Should be fixed in more recent stable kernel; let me know if not.

--b.

> 
> /data ip/32(rw,async,crossmnt,insecure,root_squash,no_subtree_check,fsid=0)
> 
> On the client (Debian unstable, kernel 2.6.38-2-amd64) I mounted the
> directory under /media(nfs4import with
> 
> # mount -t nfs4 ip:/ /media/nfs4import
> 
> After a lot running fdupes on this folder the server kernel starts
> throwing messages like this one:
> 
>   VFS: file-max limit [number] reached
> 
> After a reboot I recognised that the number of used file descriptors
> increases during the run of fdupes (see /proc/sys/fs/file-nr). Even
> after unmounting the exported filesystem on the client, unexport the
> file system on the server and stopping the nfs-server the file
> descriptors are still allocated and unmounting the filesystem is not
> possible.
> 
> After a little bit of research I could create a small program, which
> increases the used file descriptors by one.
> 
> Regards,
>   Gerhard

> #include <stdio.h>
> 
> #define DIR "/media/nfs4import/"
> 
> int main(void) {
> 	FILE *f1;
> 	FILE *f2;
> 	char b[1024];
> 	int i;
> 
> 	// create file1
> 	f1 = fopen(DIR "file1.txt", "w");
> 	fwrite("test\n", 5, 1, f1);
> 	close(f1);
> 
> 	// open file1 in read mode
> 	f1 = fopen(DIR "file1.txt", "r");
> 
> 	for (i = 0; i < 1; i++) {
> 		// open file2 in write mode and close it
> 		f2 = fopen(DIR "file2.txt", "w");
> 		fclose(f2);
> 	
> 		// open file2 in read mode and close it
> 		// this causes the leak of a file descriptor on the server
> 		// just watch /proc/sys/fs/file-nr on the server
> 		f2 = fopen(DIR "file2.txt", "r");
> 		fclose(f2);
> 	}
> 	fclose(f1);
> 
> 	return 0;
> }