net_sched: qdisc_alloc_handle() can be too slow (fa0f5aa7) · Commits · 戴 / test

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>

net/sched/sch_api.c

+9 −5

Original line number	Diff line number	Diff line
		@@ -618,20 +618,24 @@ void qdisc_class_hash_remove(struct Qdisc_class_hash *clhash,
		}
		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)

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