NFS: Fix a race in __nfs_list_for_each_server()

The struct nfs_server gets put on the cl_superblocks list before
the server->super field has been initialised, in which case the
call to nfs_sb_active() will Oops. Add a check to ensure that
we skip such a list entry.

Fixes: 3c9e502b59fb ("NFS: Add a helper nfs_client_for_each_server()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 59ef3b13ccca2521a996c776aea55363ae05bbe1..bdb6d0c2e7550bd0d20c8ceb91918a54c849da3d 100644 (file)
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -185,7 +185,7 @@ static int __nfs_list_for_each_server(struct list_head *head,
 
        rcu_read_lock();
        list_for_each_entry_rcu(server, head, client_link) {
-               if (!nfs_sb_active(server->super))
+               if (!(server->super && nfs_sb_active(server->super)))
                        continue;
                rcu_read_unlock();
                if (last)