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authorEric Dumazet <eric.dumazet@gmail.com>2010-03-31 07:06:04 +0000
committerDavid S. Miller <davem@davemloft.net>2010-04-01 18:38:48 -0700
commit5d944c640b4ae5f37c537acf491c2f0eb89fa0d6 (patch)
tree9195a0135ec21c1c06ff4d46e8cf7924e2c364c0 /net/sched
parentd4fc6dbb5ae51430e35b2005f6d68938861f8d8b (diff)
downloadlinux-5d944c640b4ae5f37c537acf491c2f0eb89fa0d6.tar.bz2
gen_estimator: deadlock fix
One of my test machine got a deadlock during "tc" sessions, adding/deleting classes & filters, using traffic estimators. After some analysis, I believe we have a potential use after free case in est_timer() : spin_lock(e->stats_lock); << HERE >> read_lock(&est_lock); if (e->bstats == NULL) << TEST >> goto skip; Test is done a bit late, because after estimator is killed, and before rcu grace period elapsed, we might already have freed/reuse memory where e->stats_locks points to (some qdisc->q.lock) A possible fix is to respect a rcu grace period at Qdisc dismantle time. On 64bit, sizeof(struct Qdisc) is exactly 192 bytes. Adding 16 bytes to it (for struct rcu_head) is a problem because it might change performance, given QDISC_ALIGNTO is 32 bytes. This is why I also change QDISC_ALIGNTO to 64 bytes, to satisfy most current alignment requirements. Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched')
-rw-r--r--net/sched/sch_generic.c15
1 files changed, 13 insertions, 2 deletions
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 5173c1e1b19c..17513252e83f 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -528,7 +528,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
unsigned int size;
int err = -ENOBUFS;
- /* ensure that the Qdisc and the private data are 32-byte aligned */
+ /* ensure that the Qdisc and the private data are 64-byte aligned */
size = QDISC_ALIGN(sizeof(*sch));
size += ops->priv_size + (QDISC_ALIGNTO - 1);
@@ -590,6 +590,13 @@ void qdisc_reset(struct Qdisc *qdisc)
}
EXPORT_SYMBOL(qdisc_reset);
+static void qdisc_rcu_free(struct rcu_head *head)
+{
+ struct Qdisc *qdisc = container_of(head, struct Qdisc, rcu_head);
+
+ kfree((char *) qdisc - qdisc->padded);
+}
+
void qdisc_destroy(struct Qdisc *qdisc)
{
const struct Qdisc_ops *ops = qdisc->ops;
@@ -613,7 +620,11 @@ void qdisc_destroy(struct Qdisc *qdisc)
dev_put(qdisc_dev(qdisc));
kfree_skb(qdisc->gso_skb);
- kfree((char *) qdisc - qdisc->padded);
+ /*
+ * gen_estimator est_timer() might access qdisc->q.lock,
+ * wait a RCU grace period before freeing qdisc.
+ */
+ call_rcu(&qdisc->rcu_head, qdisc_rcu_free);
}
EXPORT_SYMBOL(qdisc_destroy);