Re: Infinit LAYOUTGET with mmap

[Jeff Layton <jlayton@poochiereds.net>]

On Mon, 2016-05-30 at 17:51 +0200, Mkrtchyan, Tigran wrote:
> 
> re-sending, as it never arrived....
> 
> ----- Original Message -----
> > 
> > From: "Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>
> > To: "Linux NFS Mailing List" <linux-nfs@vger.kernel.org>
> > Sent: Monday, May 30, 2016 5:05:59 PM
> > Subject: Infinit LAYOUTGET with mmap
> > 
> > Dear NFS developers,
> > 
> > On my test system I hit a behavior of the nfs client with
> > kernel 4.4 which I haven't seen before.
> > 
> > 
> > Here is a minimal example to reproduce the issue:
> > 
> > ============= bug.c =====================
> > 
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <unistd.h>
> > #include <fcntl.h>
> > #include <sys/mman.h>
> > 
> > 
> > int main(int argc, char* argv[])
> > {
> > 
> >    int *m;
> >    int fd;
> >    int err;
> > 
> >    fd = open(argv[1], O_CREAT| O_RDWR, O_TRUNC, 0666);
> >    if (fd < 0) {
> >        perror("failed to open file");
> >        exit(1);
> >    }
> > 
> >    err = ftruncate(fd, 4096);
> >    if (err) {
> >        perror("cant set filesize");
> >        exit(2);
> >    }
> > 
> >    m = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> >    if (m == MAP_FAILED) {
> >        perror("failed to map the file");
> >        exit(2);
> >    }
> > 
> >    m[1] = 0;
> > 
> >    err = munmap(m, 4096);
> >    if (err) {
> >        perror("failed to unmap the file");
> >    }
> > 
> >    close(fd);
> > }
> > =============== end of example ================
> > 
> > 
> > 
> > When  running this code, client send an OPEN with share_access
> > OPEN4_SHARE_ACCESS_BOTH. But later calient sends LAYOUTGET with
> > IOMODE_READ
> > followed by GETDEVICEINFO.
> > 
> > This combination of LG+GDI remain for ever. The capture file is
> > attached.
> > 
> > My guess it that client expects RW layout.
> > 
> > Kernel: 4.4.9-300.fc23.x86_64. I will try with upstream as well.
> > 
> > Thanks a lot,
> >    Tigran.

No capture attached, but 4.7 should be getting a major overhaul to the
LAYOUTGET retry handling code. You may want to re-test with a bleeding
edge kernel and see if the problem is still present.

Cheers,
-- 
Jeff Layton <jlayton@poochiereds.net>