[PATCH net] net_sched: prio: properly report out of memory errors

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

At Qdisc creation or change time, prio_tune() creates missing
pfifo qdiscs but does not return an error code if one
qdisc could not be allocated.

Leaving a qdisc in non operational state without telling user
anything about this problem is not good.

Also, testing if we replace something different than noop_qdisc
a second time makes no sense so I removed useless code.

Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 net/sched/sch_prio.c |   32 ++++++++++++--------------------
 1 file changed, 12 insertions(+), 20 deletions(-)

diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c
index 4b0a82191bc4..071718bccdab 100644
--- a/net/sched/sch_prio.c
+++ b/net/sched/sch_prio.c
@@ -202,26 +202,18 @@ static int prio_tune(struct Qdisc *sch, struct nlattr 
*opt)
        sch_tree_unlock(sch);
 
        for (i = 0; i < q->bands; i++) {
-               if (q->queues[i] == &noop_qdisc) {
-                       struct Qdisc *child, *old;
-
-                       child = qdisc_create_dflt(sch->dev_queue,
-                                                 &pfifo_qdisc_ops,
-                                                 TC_H_MAKE(sch->handle, i + 
1));
-                       if (child) {
-                               sch_tree_lock(sch);
-                               old = q->queues[i];
-                               q->queues[i] = child;
-
-                               if (old != &noop_qdisc) {
-                                       qdisc_tree_reduce_backlog(old,
-                                                                 old->q.qlen,
-                                                                 
old->qstats.backlog);
-                                       qdisc_destroy(old);
-                               }
-                               sch_tree_unlock(sch);
-                       }
-               }
+               struct Qdisc *child;
+
+               if (q->queues[i] != &noop_qdisc)
+                       continue;
+
+               child = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
+                                         TC_H_MAKE(sch->handle, i + 1));
+               if (!child)
+                       return -ENOMEM;
+               sch_tree_lock(sch);
+               q->queues[i] = child;
+               sch_tree_unlock(sch);
        }
        return 0;
 }