From 5f121b9a83b499a61ed44e5ba619c7de8f7271ad Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Thu, 13 Jun 2013 15:29:38 -0400 Subject: net-rps: fixes for rps flow limit Caught by sparse: - __rcu: missing annotation to sd->flow_limit - __user: direct access in cpumask_scnprintf Also - add endline character when printing bitmap if room in buffer - avoid bucket overflow by reducing FLOW_LIMIT_HISTORY The last item warrants some explanation. The hashtable buckets are subject to overflow if FLOW_LIMIT_HISTORY is larger than or equal to bucket size, since all packets may end up in a single bucket. The current (rather arbitrary) history value of 256 happens to match the buffer size (u8). As a result, with a single flow, the first 128 packets are accepted (correct), the second 128 packets dropped (correct) and then the history[] array has filled, so that each subsequent new packet causes an increment in the bucket for new_flow plus a decrement for old_flow: a steady state. This is fine if packets are dropped, as the steady state goes away as soon as a mix of traffic reappears. But, because the 256th packet overflowed the bucket to 0: no packets are dropped. Instead of explicitly adding an overflow check, this patch changes FLOW_LIMIT_HISTORY to never be able to overflow a single bucket. Reported-by: Fengguang Wu (first item) Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller --- include/linux/netdevice.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index e5d65573b4d6..8c9fcc42502a 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -1840,7 +1840,7 @@ static inline int unregister_gifconf(unsigned int family) } #ifdef CONFIG_NET_FLOW_LIMIT -#define FLOW_LIMIT_HISTORY (1 << 8) /* must be ^2 */ +#define FLOW_LIMIT_HISTORY (1 << 7) /* must be ^2 and !overflow buckets */ struct sd_flow_limit { u64 count; unsigned int num_buckets; @@ -1883,7 +1883,7 @@ struct softnet_data { struct napi_struct backlog; #ifdef CONFIG_NET_FLOW_LIMIT - struct sd_flow_limit *flow_limit; + struct sd_flow_limit __rcu *flow_limit; #endif }; -- cgit v1.2.3