From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] dropmon: add ability to detect when hardware drops rx packets Date: Sat, 09 May 2009 08:30:35 +0200 Message-ID: <4A05230B.6070806@cosmosbay.com> References: <20090508195026.GB13017@hmsreliant.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org, davem@davemloft.net To: Neil Horman Return-path: Received: from gw1.cosmosbay.com ([212.99.114.194]:47757 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931AbZEIGau convert rfc822-to-8bit (ORCPT ); Sat, 9 May 2009 02:30:50 -0400 In-Reply-To: <20090508195026.GB13017@hmsreliant.think-freely.org> Sender: netdev-owner@vger.kernel.org List-ID: Neil Horman a =E9crit : > Hey all- > A few weeks back I sent out an RFC in which I proposed that I could > extend dropwatch to detect drops in hardware by adding a napi poll tr= acepoint, > using that as an indicator that I should periodically check the stats= to see if > the rx drop counter had changed. Having not had any negative feedbac= k to that > proposal, heres the patch. I've tested it and it seems to work fairl= y well. > Neil >=20 >=20 > Patch to add the ability to detect drops in hardware interfaces via d= ropwatch. > Adds a tracepoint to net_rx_action to signal everytime a napi instanc= e is > polled. The dropmon code then periodically checks to see if the rx_f= rames > counter has changed, and if so, adds a drop notification to the netli= nk > protocol, using the reserved all-0's vector to indicate the drop loca= tion was in > hardware, rather than somewhere in the code. >=20 > Signed-off-by: Neil Horman >=20 Hi Neil I dont fully understand your patch, but at least have some questions about rcu stuff. >=20 > include/linux/net_dropmon.h | 7 ++ > include/trace/napi.h | 11 ++++ > net/core/dev.c | 5 +- > net/core/drop_monitor.c | 107 +++++++++++++++++++++++++++++++++= +++++++++-- > net/core/net-traces.c | 4 + > net/core/netpoll.c | 2=20 > 6 files changed, 131 insertions(+), 5 deletions(-) >=20 > diff --git a/include/linux/net_dropmon.h b/include/linux/net_dropmon.= h > index 0217fb8..9addc62 100644 > --- a/include/linux/net_dropmon.h > +++ b/include/linux/net_dropmon.h > @@ -8,6 +8,13 @@ struct net_dm_drop_point { > __u32 count; > }; > =20 > +#define is_drop_point_hw(x) do {\ > + int ____i, ____j;\ > + for (____i =3D 0; ____i < 8; i ____i++)\ > + ____j |=3D x[____i];\ > + ____j;\ > +} while (0) > + > #define NET_DM_CFG_VERSION 0 > #define NET_DM_CFG_ALERT_COUNT 1 > #define NET_DM_CFG_ALERT_DELAY 2 > diff --git a/include/trace/napi.h b/include/trace/napi.h > new file mode 100644 > index 0000000..7c39eb7 > --- /dev/null > +++ b/include/trace/napi.h > @@ -0,0 +1,11 @@ > +#ifndef _TRACE_NAPI_H_ > +#define _TRACE_NAPI_H_ > + > +#include > +#include > + > +DECLARE_TRACE(napi_poll, > + TP_PROTO(struct napi_struct *napi), > + TP_ARGS(napi)); > + > +#endif > diff --git a/net/core/dev.c b/net/core/dev.c > index 637ea71..165979c 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -126,6 +126,7 @@ > #include > #include > #include > +#include > =20 > #include "net-sysfs.h" > =20 > @@ -2763,8 +2764,10 @@ static void net_rx_action(struct softirq_actio= n *h) > * accidently calling ->poll() when NAPI is not scheduled. > */ > work =3D 0; > - if (test_bit(NAPI_STATE_SCHED, &n->state)) > + if (test_bit(NAPI_STATE_SCHED, &n->state)) { > work =3D n->poll(n, weight); > + trace_napi_poll(n); > + } > =20 > WARN_ON_ONCE(work > weight); > =20 > diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c > index 2797b71..538c1d4 100644 > --- a/net/core/drop_monitor.c > +++ b/net/core/drop_monitor.c > @@ -22,8 +22,10 @@ > #include > #include > #include > +#include > =20 > #include > +#include > =20 > #include > =20 > @@ -38,7 +40,7 @@ static void send_dm_alert(struct work_struct *unuse= d); > * and the work handle that will send up > * netlink alerts > */ > -struct sock *dm_sock; > +static int trace_state =3D TRACE_OFF; > =20 > struct per_cpu_dm_data { > struct work_struct dm_alert_work; > @@ -47,6 +49,12 @@ struct per_cpu_dm_data { > struct timer_list send_timer; > }; > =20 > +struct dm_hw_stat_delta { > + struct net_device *dev; > + struct list_head list; > + unsigned long last_drop_val; > +}; > + > static struct genl_family net_drop_monitor_family =3D { > .id =3D GENL_ID_GENERATE, > .hdrsize =3D 0, > @@ -59,7 +67,8 @@ static DEFINE_PER_CPU(struct per_cpu_dm_data, dm_cp= u_data); > =20 > static int dm_hit_limit =3D 64; > static int dm_delay =3D 1; > - > +static unsigned long dm_hw_check_delta =3D 2*HZ; > +static LIST_HEAD(hw_stats_list); > =20 > static void reset_per_cpu_data(struct per_cpu_dm_data *data) > { > @@ -115,7 +124,7 @@ static void sched_send_work(unsigned long unused) > schedule_work(&data->dm_alert_work); > } > =20 > -static void trace_kfree_skb_hit(struct sk_buff *skb, void *location) > +static void trace_drop_common(struct sk_buff *skb, void *location) > { > struct net_dm_alert_msg *msg; > struct nlmsghdr *nlh; > @@ -159,18 +168,59 @@ out: > return; > } > =20 > +static void trace_kfree_skb_hit(struct sk_buff *skb, void *location) > +{ > + trace_drop_common(skb, location); > +} > + > +static void trace_napi_poll_hit(struct napi_struct *napi) > +{ > + struct dm_hw_stat_delta *new_stat; > + > + /* > + * Ratelimit our check time to dm_hw_check_delta jiffies > + */ > + if (!time_after(jiffies, napi->dev->last_rx + dm_hw_check_delta)) > + return; > + > + list_for_each_entry_rcu(new_stat, &hw_stats_list, list) { > + if ((new_stat->dev =3D=3D napi->dev) && > + (napi->dev->stats.rx_dropped !=3D new_stat->last_drop_val)) { > + trace_drop_common(NULL, NULL); > + new_stat->last_drop_val =3D napi->dev->stats.rx_dropped; > + break; > + } > + } > +} > + > + > static int set_all_monitor_traces(int state) > { > int rc =3D 0; > + struct dm_hw_stat_delta *new_stat =3D NULL; > =20 > switch (state) { > case TRACE_ON: > rc |=3D register_trace_kfree_skb(trace_kfree_skb_hit); > + rc |=3D register_trace_napi_poll(trace_napi_poll_hit); > break; > case TRACE_OFF: > rc |=3D unregister_trace_kfree_skb(trace_kfree_skb_hit); > + rc |=3D unregister_trace_napi_poll(trace_napi_poll_hit); > =20 > tracepoint_synchronize_unregister(); > + > + /* > + * Clean the device list > + */ > + rcu_read_lock(); > + list_for_each_entry_rcu(new_stat, &hw_stats_list, list) { > + if (new_stat->dev =3D=3D NULL) { > + list_del_rcu(&new_stat->list); > + kfree(new_stat); I can't see how list_del_rcu(&new_stat->list) can be followed by kfree= (new_stat) safely. You need a grace period between two operations. That can be don= e with call_rcu() helper. Also, rcu_read_lock()/rcu_read_unlock() is not the proper locking pragm= as needed here. multiple writers are/should be forbidden here. If caller a= lready does a locking, then no additional locking is needed here. > + } > + } > + rcu_read_unlock(); > break; > default: > rc =3D 1; > @@ -179,6 +229,7 @@ static int set_all_monitor_traces(int state) > =20 > if (rc) > return -EINPROGRESS; > + trace_state =3D state; > return rc; > } > =20 > @@ -204,6 +255,43 @@ static int net_dm_cmd_trace(struct sk_buff *skb, > return -ENOTSUPP; > } > =20 > +int dropmon_net_event(struct notifier_block *ev_block, > + unsigned long event, void *ptr) > +{ > + struct net_device *dev =3D ptr; > + struct dm_hw_stat_delta *new_stat =3D NULL; > + > + > + switch (event) { > + case NETDEV_REGISTER: > + new_stat =3D kzalloc(sizeof(struct dm_hw_stat_delta), GFP_KERNEL); > + > + if (!new_stat) > + goto out; > + > + new_stat->dev =3D dev; > + rcu_read_lock(); same point here, rcu_read_lock is not the proper way to protect the lis= t. > + list_add_rcu(&new_stat->list, &hw_stats_list); > + rcu_read_unlock(); > + break; > + case NETDEV_UNREGISTER: > + list_for_each_entry_rcu(new_stat, &hw_stats_list, list) { > + if (new_stat->dev =3D=3D dev) > + new_stat->dev =3D NULL; > + break; > + } > + > + if (trace_state =3D=3D TRACE_OFF) { > + rcu_read_lock(); > + list_del_rcu(&new_stat->list); > + rcu_read_unlock(); > + kfree(new_stat); same probleme here. If rcu is used, then you need a grace period. > + } > + break; > + } > +out: > + return NOTIFY_DONE; > +} > =20 > static struct genl_ops dropmon_ops[] =3D { > { > @@ -220,6 +308,10 @@ static struct genl_ops dropmon_ops[] =3D { > }, > }; > =20 > +static struct notifier_block dropmon_net_notifier =3D { > + .notifier_call =3D dropmon_net_event > +}; > + > static int __init init_net_drop_monitor(void) > { > int cpu; > @@ -243,12 +335,18 @@ static int __init init_net_drop_monitor(void) > ret =3D genl_register_ops(&net_drop_monitor_family, > &dropmon_ops[i]); > if (ret) { > - printk(KERN_CRIT "failed to register operation %d\n", > + printk(KERN_CRIT "Failed to register operation %d\n", > dropmon_ops[i].cmd); > goto out_unreg; > } > } > =20 > + rc =3D register_netdevice_notifier(&dropmon_net_notifier); > + if (rc < 0) { > + printk(KERN_CRIT "Failed to register netdevice notifier\n"); > + goto out_unreg; > + } > + > rc =3D 0; > =20 > for_each_present_cpu(cpu) { > @@ -259,6 +357,7 @@ static int __init init_net_drop_monitor(void) > data->send_timer.data =3D cpu; > data->send_timer.function =3D sched_send_work; > } > + > goto out; > =20 > out_unreg: > diff --git a/net/core/net-traces.c b/net/core/net-traces.c > index c8fb456..b07b25b 100644 > --- a/net/core/net-traces.c > +++ b/net/core/net-traces.c > @@ -20,6 +20,7 @@ > #include > #include > #include > +#include > =20 > #include > #include > @@ -27,3 +28,6 @@ > =20 > DEFINE_TRACE(kfree_skb); > EXPORT_TRACEPOINT_SYMBOL_GPL(kfree_skb); > + > +DEFINE_TRACE(napi_poll); > +EXPORT_TRACEPOINT_SYMBOL_GPL(napi_poll); > diff --git a/net/core/netpoll.c b/net/core/netpoll.c > index b5873bd..446d3ba 100644 > --- a/net/core/netpoll.c > +++ b/net/core/netpoll.c > @@ -24,6 +24,7 @@ > #include > #include > #include > +#include > =20 > /* > * We maintain a small pool of fully-sized skbs, to make sure the > @@ -137,6 +138,7 @@ static int poll_one_napi(struct netpoll_info *npi= nfo, > set_bit(NAPI_STATE_NPSVC, &napi->state); > =20 > work =3D napi->poll(napi, budget); > + trace_napi_poll(napi->dev); > =20 > clear_bit(NAPI_STATE_NPSVC, &napi->state); > atomic_dec(&trapped); >=20