net_sched: qdisc_alloc_handle() can be too slow
When trying to allocate ~32768 qdiscs using autohandle mechanism, we can
fill the space managed by kernel (handles in [8000-FFFF]:0000 range)
But O(N^2) qdisc_alloc_handle() loops 0x10000 times instead of 0x8000
time tc add qdisc add dev eth0 parent 10:7fff pfifo limit 10
RTNETLINK answers: Cannot allocate memory
real 1m54.826s
user 0m0.000s
sys 0m0.004s
INFO: rcu_sched_state detected stall on CPU 0 (t=60000 jiffies)
Half number of loops, and add a cond_resched() call.
We hold rtnl at this point.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Dave Taht <dave.taht@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index dca6c1a5..3d8981f 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -618,20 +618,24 @@
}
EXPORT_SYMBOL(qdisc_class_hash_remove);
-/* Allocate an unique handle from space managed by kernel */
-
+/* Allocate an unique handle from space managed by kernel
+ * Possible range is [8000-FFFF]:0000 (0x8000 values)
+ */
static u32 qdisc_alloc_handle(struct net_device *dev)
{
- int i = 0x10000;
+ int i = 0x8000;
static u32 autohandle = TC_H_MAKE(0x80000000U, 0);
do {
autohandle += TC_H_MAKE(0x10000U, 0);
if (autohandle == TC_H_MAKE(TC_H_ROOT, 0))
autohandle = TC_H_MAKE(0x80000000U, 0);
- } while (qdisc_lookup(dev, autohandle) && --i > 0);
+ if (!qdisc_lookup(dev, autohandle))
+ return autohandle;
+ cond_resched();
+ } while (--i > 0);
- return i > 0 ? autohandle : 0;
+ return 0;
}
void qdisc_tree_decrease_qlen(struct Qdisc *sch, unsigned int n)
