NFSv4.1/pnfs: Fix atomicity of commit list updates

pnfs_layout_mark_request_commit() needs to ensure that it adds the
request to the commit list atomically with all the other updates
in order to prevent corruption to buckets[ds_commit_idx].wlseg
due to races with pnfs_generic_clear_request_commit().

Fixes: 338d00cfef07d ("pnfs: Refactor the *_layout_mark_request_commit...")
Cc: stable@vger.kernel.org # v4.0+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --cc fs/nfs/internal.h
Simple merge

diff --cc fs/nfs/pnfs_nfs.c
Simple merge

diff --cc fs/nfs/write.c
Simple merge