Without this patch, it is possible to hang the NFSv4 client,
when a rename/remove is being done on a file where the client
holds a delegation, if pNFS is being used. For a delegation
to be returned, dirty data blocks must be flushed to the NFSv4
server. When pNFS is in use, a shared lock on the clientID
must be acquired while doing a write to the DS(s).
However, if rename/remove is doing the delegation return
an exclusive lock will be acquired on the clientID, preventing
the write to the DS(s) from acquiring a shared lock on the clientID.
This patch stops rename/remove from doing a delegation return
if pNFS is enabled. Since doing delegation return in the same
compound as rename/remove is only an optimization, not doing
so should not cause problems.
This problem was detected during a recent NFSv4 interoperability
testing event held by the IETF working group.
MFC after: 1 week
b82168e657