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net_sched: qdisc_alloc_handle() can be too slow

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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>
This commit is contained in:
Eric Dumazet
2012-01-03 00:00:11 +00:00
committed by David S. Miller
parent d32ae76f2b
commit fa0f5aa743
1 changed files with 9 additions and 5 deletions
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14
net/sched/sch_api.c
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@@ -618,20 +618,24 @@ void qdisc_class_hash_remove(struct Qdisc_class_hash *clhash,
} }
EXPORT_SYMBOL(qdisc_class_hash_remove); 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) static u32 qdisc_alloc_handle(struct net_device *dev)
{ {
int i = 0x10000; int i = 0x8000;
static u32 autohandle = TC_H_MAKE(0x80000000U, 0); static u32 autohandle = TC_H_MAKE(0x80000000U, 0);
do { do {
autohandle += TC_H_MAKE(0x10000U, 0); autohandle += TC_H_MAKE(0x10000U, 0);
if (autohandle == TC_H_MAKE(TC_H_ROOT, 0)) if (autohandle == TC_H_MAKE(TC_H_ROOT, 0))
autohandle = TC_H_MAKE(0x80000000U, 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) void qdisc_tree_decrease_qlen(struct Qdisc *sch, unsigned int n)