nfsd: fix race in nfsd_nrthreads()

We need the nfsd_mutex before accessing nfsd_serv->sv_nrthreads or we
can't even guarantee nfsd_serv will still be there.

Signed-off-by: Neil Brown <neilb@suse.de>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 6 insertions, 4 deletions

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 26c81149d49a..96fdbcab8d95 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -165,10 +165,12 @@ int nfsd_vers(int vers, enum vers_op change)
 
 int nfsd_nrthreads(void)
 {
-        if (nfsd_serv == NULL)
-                return 0;
-        else
-                return nfsd_serv->sv_nrthreads;
+        int rv = 0;
+        mutex_lock(&nfsd_mutex);
+        if (nfsd_serv)
+                rv = nfsd_serv->sv_nrthreads;
+        mutex_unlock(&nfsd_mutex);
+        return rv;
 }
 
 static void nfsd_last_thread(struct svc_serv *serv)