dlm: use rwlock for rsb hash table

The conversion to rhashtable introduced a hash table lock per lockspace,
in place of per bucket locks.  To make this more scalable, switch to
using a rwlock for hash table access.  The common case fast path uses
it as a read lock.

Signed-off-by: Alexander Aring <[email protected]>
Signed-off-by: David Teigland <[email protected]>

Author: Alexander Aring

fs/dlm/debug_fs.c

@@ -413,7 +413,7 @@ static void *table_seq_start(struct seq_file *seq, loff_t *pos)
 	else
 		list = &ls->ls_keep;
 
-	spin_lock_bh(&ls->ls_rsbtbl_lock);
+	read_lock_bh(&ls->ls_rsbtbl_lock);
 	return seq_list_start(list, *pos);
 }
 
@@ -434,7 +434,7 @@ static void table_seq_stop(struct seq_file *seq, void *iter_ptr)
 {
 	struct dlm_ls *ls = seq->private;
 
-	spin_unlock_bh(&ls->ls_rsbtbl_lock);
+	read_unlock_bh(&ls->ls_rsbtbl_lock);
 }
 
 static const struct seq_operations format1_seq_ops = {

fs/dlm/dir.c

@@ -200,9 +200,9 @@ static struct dlm_rsb *find_rsb_root(struct dlm_ls *ls, const char *name,
 	struct dlm_rsb *r;
 	int rv;
 
-	spin_lock_bh(&ls->ls_rsbtbl_lock);
+	read_lock_bh(&ls->ls_rsbtbl_lock);
 	rv = dlm_search_rsb_tree(&ls->ls_rsbtbl, name, len, &r);
-	spin_unlock_bh(&ls->ls_rsbtbl_lock);
+	read_unlock_bh(&ls->ls_rsbtbl_lock);
 	if (!rv)
 		return r;
 

fs/dlm/dlm_internal.h

@@ -585,7 +585,7 @@ struct dlm_ls {
 	spinlock_t		ls_lkbidr_spin;
 
 	struct rhashtable	ls_rsbtbl;
-	spinlock_t		ls_rsbtbl_lock;
+	rwlock_t		ls_rsbtbl_lock;
 
 	struct list_head	ls_toss;
 	struct list_head	ls_keep;