3.14.27 client hang on specific file

[Brian De Wolf <bldewolf@cpp.edu>]

Hello,

After updating our kernel from 3.4.x to 3.14.27 (along with nfs-utils
1.2.9), we've had a strange issue with our sec=krb5p NFSv4 mounts.
My initial light testing went fine, but sometimes, on any given host, a
specific file will no longer be accessible.  Any attempt to access it
causes the process to go into uninterruptible sleep.

Reproducing this on another host was fairly quick by dd'ing 30MB
from /dev/zero into a file repeatedly.  Eventually the dd hangs instead
of completing.  Once broken, the simplest test I could think of was
"stat testfile".  tcpdump shows no traffic when I run it.  Turning
rpcdebug all the way up produces:

	kernel: RPC:       looking up Generic cred
	kernel: NFS: permission(0:28/3), mask=0x1, res=0
	kernel: NFS: nfs_lookup_revalidate(/testfile) is valid

Around the time that it breaks, it also prints

	kernel: nfs: server servername not responding, still trying

several times, but I couldn't find a way to get it to print it again.
It doesn't look like it follows up with more timeouts or an "OK", so
that seems pretty odd.

Anyone have any ideas?  I'm happy to provide more debug info.


Thanks,
Brian