[PATCH 5/6] nfs_localio: duplicate nfs_close_local_fh()

[NeilBrown <neil@brown.name>]

nfs_close_local_fh() is called from two different places for quite
different use case.

It is called from nfs_uuid_put() when the nfs_uuid is being detached -
possibly because the nfs server is not longer serving that filesystem.
In this case there will always be an nfs_uuid and so rcu_read_lock() is
not needed.

It is also called when the nfs_file_localio is no longer needed.  In
this case there may not be an active nfs_uuid.

These two can race, and handling the race properly while avoiding
excessive locking will require different handling on each side.

This patch prepares the way by opencoding nfs_close_local_fh() into
nfs_uuid_put(), then simplifying the code there as befits the context.

Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client")
Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/nfs_common/nfslocalio.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c
index cbf3e38443f9..abf1591a3b7f 100644
--- a/fs/nfs_common/nfslocalio.c
+++ b/fs/nfs_common/nfslocalio.c
@@ -171,7 +171,24 @@ static bool nfs_uuid_put(nfs_uuid_t *nfs_uuid)
 
 	/* Walk list of files and ensure their last references dropped */
 	list_for_each_entry_safe(nfl, tmp, &local_files, list) {
-		nfs_close_local_fh(nfl);
+		struct nfsd_file __rcu *ro_nf;
+		struct nfsd_file __rcu *rw_nf;
+
+		ro_nf = xchg(&nfl->ro_file, RCU_INITIALIZER(NULL));
+		rw_nf = xchg(&nfl->rw_file, RCU_INITIALIZER(NULL));
+
+		spin_lock(&nfs_uuid->lock);
+		/* Remove nfl from nfs_uuid->files list */
+		list_del_init(&nfl->list);
+		spin_unlock(&nfs_uuid->lock);
+		/* Now we can allow racing nfs_close_local_fh() to
+		 * skip the locking.
+		 */
+		RCU_INIT_POINTER(nfl->nfs_uuid, NULL);
+
+		nfs_to_nfsd_file_put_local(ro_nf);
+		nfs_to_nfsd_file_put_local(rw_nf);
+
 		cond_resched();
 	}
 
-- 
2.49.0