Revert "nfsd: fix oops when reading pool_stats before server is started"

This reverts commit 8e948c36.

The reverted commit moves a test on a field protected by a mutex outside
of the protection of that mutex, and so is obviously racey.

Depending on how the race goes, si->serv might be NULL when dereferenced
in svc_pool_stats_start(), or svc_pool_stats_stop() might unlock a mutex
that hadn't been locked.

This bug that the commit tried to fix has been addressed by initialising
->mutex earlier.

Fixes: 8e948c36 ("nfsd: fix oops when reading pool_stats before server is started")
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/svc_xprt.c

@@ -1421,13 +1421,12 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
 
 	dprintk("svc_pool_stats_start, *pidx=%u\n", pidx);
 
-	if (!si->serv)
-		return NULL;
-
 	mutex_lock(si->mutex);
 
 	if (!pidx)
 		return SEQ_START_TOKEN;
+	if (!si->serv)
+		return NULL;
 	return pidx > si->serv->sv_nrpools ? NULL
 		: &si->serv->sv_pools[pidx - 1];
 }
@@ -1459,8 +1458,7 @@ static void svc_pool_stats_stop(struct seq_file *m, void *p)
 {
 	struct svc_info *si = m->private;
 
-	if (si->serv)
-		mutex_unlock(si->mutex);
+	mutex_unlock(si->mutex);
 }
 
 static int svc_pool_stats_show(struct seq_file *m, void *p)