[NET_SCHED] sch_api: fix qdisc_tree_decrease_qlen() loop

TC_H_MAJ(parentid) for root classes is the same as for ingress, and if
ingress qdisc is created qdisc_lookup() returns its pointer (without
ingress NULL is returned). After this all qdisc_lookups give the same,
and we get endless loop. (I don't know how this could hide for so long
- it should trigger with every leaf class deleted if it's qdisc isn't
empty.)

After this fix qdisc_lookup() is omitted both for ingress and root
parents, but looking for root is only wasting a little time here...
Many thanks to Enrico Demarin for finding a test for catching this
bug, which probably bothered quite a lot of admins.

Reported-by: Enrico Demarin <enrico@superclick.com>,
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 7e3c048..fc8708a 100644 (file)
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -386,6 +386,9 @@ void qdisc_tree_decrease_qlen(struct Qdisc *sch, unsigned int n)
        if (n == 0)
                return;
        while ((parentid = sch->parent)) {
+               if (TC_H_MAJ(parentid) == TC_H_MAJ(TC_H_INGRESS))
+                       return;
+
                sch = qdisc_lookup(sch->dev, TC_H_MAJ(parentid));
                if (sch == NULL) {
                        WARN_ON(parentid != TC_H_ROOT);