pkt_sched: fq: do not hold qdisc lock while allocating memory

[ Upstream commit 2d8d40af ]

Resizing fq hash table allocates memory while holding qdisc spinlock,
with BH disabled.

This is definitely not good, as allocation might sleep.

We can drop the lock and get it when needed, we hold RTNL so no other
changes can happen at the same time.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: afe4fd06 ("pkt_sched: fq: Fair Queue packet scheduler")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

net/sched/sch_fq.c

@@ -577,9 +577,11 @@ static void fq_rehash(struct fq_sched_data *q,
 	q->stat_gc_flows += fcnt;
 }
 
-static int fq_resize(struct fq_sched_data *q, u32 log)
+static int fq_resize(struct Qdisc *sch, u32 log)
 {
+	struct fq_sched_data *q = qdisc_priv(sch);
 	struct rb_root *array;
+	void *old_fq_root;
 	u32 idx;
 
 	if (q->fq_root && log == q->fq_trees_log)
@@ -592,13 +594,19 @@ static int fq_resize(struct fq_sched_data *q, u32 log)
 	for (idx = 0; idx < (1U << log); idx++)
 		array[idx] = RB_ROOT;
 
-	if (q->fq_root) {
-		fq_rehash(q, q->fq_root, q->fq_trees_log, array, log);
-		kfree(q->fq_root);
-	}
+	sch_tree_lock(sch);
+
+	old_fq_root = q->fq_root;
+	if (old_fq_root)
+		fq_rehash(q, old_fq_root, q->fq_trees_log, array, log);
+
 	q->fq_root = array;
 	q->fq_trees_log = log;
 
+	sch_tree_unlock(sch);
+
+	kfree(old_fq_root);
+
 	return 0;
 }
 
@@ -674,9 +682,11 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt)
 		q->flow_refill_delay = usecs_to_jiffies(usecs_delay);
 	}
 
-	if (!err)
-		err = fq_resize(q, fq_log);
-
+	if (!err) {
+		sch_tree_unlock(sch);
+		err = fq_resize(sch, fq_log);
+		sch_tree_lock(sch);
+	}
 	while (sch->q.qlen > sch->limit) {
 		struct sk_buff *skb = fq_dequeue(sch);
 
@@ -722,7 +732,7 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt)
 	if (opt)
 		err = fq_change(sch, opt);
 	else
-		err = fq_resize(q, q->fq_trees_log);
+		err = fq_resize(sch, q->fq_trees_log);
 
 	return err;
 }