rhashtable: add schedule points

BugLink: https://bugs.launchpad.net/bugs/1818806

commit ae6da1f5 upstream.

Rehashing and destroying large hash table takes a lot of time,
and happens in process context. It is safe to add cond_resched()
in rhashtable_rehash_table() and rhashtable_free_and_destroy()
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

lib/rhashtable.c

@@ -250,8 +250,10 @@ static int rhashtable_rehash_table(struct rhashtable *ht)
 	if (!new_tbl)
 		return 0;
 
-	for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
+	for (old_hash = 0; old_hash < old_tbl->size; old_hash++) {
 		rhashtable_rehash_chain(ht, old_hash);
+		cond_resched();
+	}
 
 	/* Publish the new table pointer. */
 	rcu_assign_pointer(ht->tbl, new_tbl);
@@ -842,6 +844,7 @@ void rhashtable_free_and_destroy(struct rhashtable *ht,
 		for (i = 0; i < tbl->size; i++) {
 			struct rhash_head *pos, *next;
 
+			cond_resched();
 			for (pos = rht_dereference(tbl->buckets[i], ht),
 			     next = !rht_is_a_nulls(pos) ?
 					rht_dereference(pos->next, ht) : NULL;