nfsd: filecache: remove race handling.

The race that this code tries to protect against is not interesting.
The code is problematic as we access the "nf" after we have given our
reference to the lru system.  While that takes 2+ seconds to free
things, it is still poor form.

The only interesting race I can find would be with
nfsd_file_close_inode_sync();
This is the only place that really doesn't want the file to stay on the
LRU when unhashed (which is the direct consequence of the race).

However for the race to happen, some other thread must own a reference
to a file and be putting it while nfsd_file_close_inode_sync() is trying
to close all files for an inode.  If this is possible, that other thread
could simply call nfsd_file_put() a little bit later and the result
would be the same: not all files are closed when
nfsd_file_close_inode_sync() completes.

If this was really a problem, we would need to wait in close_inode_sync
for the other references to be dropped.  We probably don't want to do
that.

So it is best to simply remove this code.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: neilbrown

fs/nfsd/filecache.c

@@ -370,22 +370,8 @@ nfsd_file_put(struct nfsd_file *nf)
 		if (refcount_dec_not_one(&nf->nf_ref))
 			return;
 
-		/* Try to add it to the LRU.  If that fails, decrement. */
-		if (nfsd_file_lru_add(nf)) {
-			/* If it's still hashed, we're done */
-			if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) {
-				nfsd_file_schedule_laundrette();
-				return;
-			}
-
-			/*
-			 * We're racing with unhashing, so try to remove it from
-			 * the LRU. If removal fails, then someone else already
-			 * has our reference.
-			 */
-			if (!nfsd_file_lru_remove(nf))
-				return;
-		}
+		if (nfsd_file_lru_add(nf))
+			return;
 	}
 	if (refcount_dec_and_test(&nf->nf_ref))
 		nfsd_file_free(nf);