netdev - [PATCH] sfq: deadlock in error path

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Message-ID: <20110202171951.09b89d92@nehalam>
Date:	Wed, 2 Feb 2011 17:19:51 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>
Cc:	netdev@...r.kernel.org
Subject: [PATCH] sfq: deadlock in error path

The change to allow divisor to be a parameter (in 2.6.38-rc1)
 commit 817fb15dfd988d8dda916ee04fa506f0c466b9d6
introduced a possible deadlock caught by sparse.

The scheduler tree lock was left locked in the case of an incorrect
divisor value. Simplest fix is to move test outside of lock
which also solves problem of partial update.

Signed-off-by: Stephen Hemminger <shemminger@...tta.com>

--- a/net/sched/sch_sfq.c	2011-02-02 17:12:06.338204106 -0800
+++ b/net/sched/sch_sfq.c	2011-02-02 17:13:39.127205019 -0800
@@ -491,17 +491,18 @@ static int sfq_change(struct Qdisc *sch,
 	if (opt->nla_len < nla_attr_size(sizeof(*ctl)))
 		return -EINVAL;
 
+	if (ctl->divisor &&
+	    (!is_power_of_2(ctl->divisor) || ctl->divisor > 65536))
+		return -EINVAL;
+
 	sch_tree_lock(sch);
 	q->quantum = ctl->quantum ? : psched_mtu(qdisc_dev(sch));
 	q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
 	q->perturb_period = ctl->perturb_period * HZ;
 	if (ctl->limit)
 		q->limit = min_t(u32, ctl->limit, SFQ_DEPTH - 1);
-	if (ctl->divisor) {
-		if (!is_power_of_2(ctl->divisor) || ctl->divisor > 65536)
-			return -EINVAL;
+	if (ctl->divisor)
 		q->divisor = ctl->divisor;
-	}
 	qlen = sch->q.qlen;
 	while (sch->q.qlen > q->limit)
 		sfq_drop(sch);
--
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