net_sched: qdisc_alloc_handle() can be too slow
authorEric Dumazet <eric.dumazet@gmail.com>
Tue, 3 Jan 2012 00:00:11 +0000 (00:00 +0000)
committerDavid S. Miller <davem@davemloft.net>
Tue, 3 Jan 2012 18:03:20 +0000 (13:03 -0500)
commitfa0f5aa74316c636427ac92dad0bc5714c34ca17
tree64fcb6a7f4043cdaea4a13b730a1ca651190e314
parentd32ae76f2b776347051cf821ebe690602e38dfc7
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>
net/sched/sch_api.c