NFS: nfsiod should not block forever in mempool_alloc()

NFS: nfsiod should not block forever in mempool_alloc()

BugLink: https://bugs.launchpad.net/bugs/1969107
[ Upstream commit 515dcdcd48736576c6f5c197814da6f81c60a21e ]

The concern is that since nfsiod is sometimes required to kick off a
commit, it can get locked up waiting forever in mempool_alloc() instead
of failing gracefully and leaving the commit until later.

Try to allocate from the slab first, with GFP_KERNEL | __GFP_NORETRY,
then fall back to a non-blocking attempt to allocate from the memory
pool.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit da747de6859948e75bcaaa1019ef0f7fdaf0b867)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>