Re: [RFC net-next] openvswitch: add trace points

Aaron Conole
2021-06-14T13:28:58Z

Eelco Chaudron <echaudro@redhat.com> writes:

> On 27 May 2021, at 21:15, Aaron Conole wrote:
>
> This makes openvswitch module use the event tracing framework
> to log the upcall interface and action execution pipeline. When
> using openvswitch as the packet forwarding engine, some types of
> debugging are made possible simply by using the ovs-vswitchd's
> ofproto/trace command. However, such a command has some
> limitations:
>
> 1. When trying to trace packets that go through the CT action,
> the state of the packet can't be determined, and probably
> would be potentially wrong.
>
> 2. Deducing problem packets can sometimes be difficult as well
> even if many of the flows are known
>
> 3. It's possible to use the openvswitch module even without
> the ovs-vswitchd (although, not common use).
>
> Introduce the event tracing points here to make it possible for
> working through these problems in kernel space. The style is
> copied from the mac80211 driver-trace / trace code for
> consistency.
>
> Thanks for doing this Aaron, it will definitely help when trying to debug some customer issues.

Thanks for the review!

> Just to be sure, I did some tests to make sure these changes do not impact performance, and it looks fine! See some
> small nits/comments below, but other than that I would say please re-send as an official patch.
>
> Cheers,
>
> Eelco
>
> Signed-off-by: Aaron Conole <aconole@redhat.com>
> ---
> net/openvswitch/Makefile | 3 +
> net/openvswitch/actions.c | 4 +
> net/openvswitch/datapath.c | 7 ++
> net/openvswitch/openvswitch_trace.c | 10 ++
> net/openvswitch/openvswitch_trace.h | 152 ++++++++++++++++++++++++++++
> 5 files changed, 176 insertions(+)
> create mode 100644 net/openvswitch/openvswitch_trace.c
> create mode 100644 net/openvswitch/openvswitch_trace.h
>
> diff --git a/net/openvswitch/Makefile b/net/openvswitch/Makefile
> index 41109c326f3a..28982630bef3 100644
> --- a/net/openvswitch/Makefile
> +++ b/net/openvswitch/Makefile
> @@ -13,6 +13,7 @@ openvswitch-y := \
> flow_netlink.o \
> flow_table.o \
> meter.o \
> + openvswitch_trace.o \
> vport.o \
> vport-internal_dev.o \
> vport-netdev.o
> @@ -24,3 +25,5 @@ endif
> obj-$(CONFIG_OPENVSWITCH_VXLAN)+= vport-vxlan.o
> obj-$(CONFIG_OPENVSWITCH_GENEVE)+= vport-geneve.o
> obj-$(CONFIG_OPENVSWITCH_GRE) += vport-gre.o
> +
> +CFLAGS_openvswitch_trace.o = -I$(src)
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index d858ea580e43..62285453ca79 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -30,6 +30,7 @@
> #include "conntrack.h"
> #include "vport.h"
> #include "flow_netlink.h"
> +#include "openvswitch_trace.h"
>
> struct deferred_action {
> struct sk_buff *skb;
> @@ -1242,6 +1243,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> a = nla_next(a, &rem)) {
> int err = 0;
>
> + if (trace_openvswitch_probe_action_enabled())
> + trace_openvswitch_probe_action(dp, skb, key, a, rem);
> +
> switch (nla_type(a)) {
> case OVS_ACTION_ATTR_OUTPUT: {
> int port = nla_get_u32(a);
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index 9d6ef6cb9b26..63f19a6ed472 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -43,6 +43,7 @@
> #include "flow_table.h"
> #include "flow_netlink.h"
> #include "meter.h"
> +#include "openvswitch_trace.h"
> #include "vport-internal_dev.h"
> #include "vport-netdev.h"
>
> @@ -275,6 +276,12 @@ int ovs_dp_upcall(struct datapath *dp, struct sk_buff *skb,
> struct dp_stats_percpu *stats;
> int err;
>
> + if (trace_openvswitch_probe_userspace_enabled()) {
> + struct sw_flow_key ukey = *key;
> +
> + trace_openvswitch_probe_userspace(dp, skb, &ukey, upcall_info);
> + }
>
> Rather than work around the const here, can we not fix this in the trace include?

Done.

> TP_PROTO(struct datapath *dp, struct sk_buff *skb,
>
> * struct sw_flow_key *key,
>
> * const struct sw_flow_key *key,
> const struct dp_upcall_info *upcall_info),
>
> @@ -97,7 +97,7 @@ TRACE_EVENT(openvswitch_probe_userspace,
> __field( u16, gso_type )
> __field( u32, ovs_flow_hash )
> __field( u32, recirc_id )
>
> * __field( void *, keyaddr )
>
> * __field( const void *, keyaddr )
> __field( u16, key_eth_type )
>
> +
> if (upcall_info->portid == 0) {
> err = -ENOTCONN;
> goto err;
> diff --git a/net/openvswitch/openvswitch_trace.c b/net/openvswitch/openvswitch_trace.c
> new file mode 100644
> index 000000000000..62c5f7d6f023
> --- /dev/null
> +++ b/net/openvswitch/openvswitch_trace.c
> @@ -0,0 +1,10 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* bug in tracepoint.h, it should include this */
> +#include <linux/module.h>
> +
> +/* sparse isn't too happy with all macros... */
> +#ifndef __CHECKER__
> +#define CREATE_TRACE_POINTS
> +#include "openvswitch_trace.h"
> +
> +#endif
> diff --git a/net/openvswitch/openvswitch_trace.h b/net/openvswitch/openvswitch_trace.h
> new file mode 100644
> index 000000000000..1b350306f622
> --- /dev/null
> +++ b/net/openvswitch/openvswitch_trace.h
> @@ -0,0 +1,152 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM openvswitch
> +
> +#if !defined(_TRACE_OPENVSWITCH_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_OPENVSWITCH_H
> +
> +#include <linux/tracepoint.h>
> +
> +#include "datapath.h"
> +
>
> I guess the naming of the events can be a long debate :) But I think just adding the word “probe” doesn’t help much.
>
> Maybe for just for function entry/exit, we could do something like <subsys>_<function_name>_entry/exit. I’ve seen
> this used in other components. For example:
>
> openvswitch_probe_userspace -> openvswitch_ovs_dp_upcall_entry
>
> For none entry/exit trace macros, we could either use a specific name, as we have:
>
> openvswitch_probe_action -> openvswitch_execute_action
>
> Or maybe even prepended by the function name to easily locate it. For example:
>
> openvswitch_probe_action -> openvswitch_do_execute_actions__execute_action
>
> I like the double underscore to differentiate, so it might even be nice for the __entry, so
> openvswitch_ovs_dp_upcall__entry.
>
> Maybe we should also change openvswitch to ovs for both system and events? Or is this too short and might cause
> confusion?

I agree that we can make these more descriptive, and that 'probe'
doesn't add much. OTOH, if I use
"openvswitch_do_execute_actions__execute_action" or the corresponding
upcall trace point name, the line lengths balloon. I don't see that
it's as useful to say both 'do_execute_actions' and '__execute_action' -
I don't think there will ever be a reason to add an additional
tracepoint here since the bulk of processing happens during the action
loop. But maybe something like:

'openvswitch_execute_action'

and

'openvswitch_dp_upcall'

?

Just want to get this part right.

> +TRACE_EVENT(openvswitch_probe_action,
> +
> + TP_PROTO(struct datapath *dp, struct sk_buff *skb,
> + struct sw_flow_key *key, const struct nlattr *a, int rem),
> +
> + TP_ARGS(dp, skb, key, a, rem),
> +
> + TP_STRUCT__entry(
> + __field( void *, dpaddr )
> + __string( dp_name, ovs_dp_name(dp) )
> + __string( dev_name, skb->dev->name )
> + __field( void *, skbaddr )
> + __field( unsigned int, len )
> + __field( unsigned int, data_len )
> + __field( unsigned int, truesize )
> + __field( u8, nr_frags )
> + __field( u16, gso_size )
> + __field( u16, gso_type )
> + __field( u32, ovs_flow_hash )
> + __field( u32, recirc_id )
> + __field( void *, keyaddr )
> + __field( u16, key_eth_type )
> + __field( u8, key_ct_state )
> + __field( u8, key_ct_orig_proto )
> + __field( unsigned int, flow_key_valid )
> + __field( u8, action_type )
> + __field( unsigned int, action_len )
> + __field( void *, action_data )
> + __field( u8, is_last )
> + ),
> +
> + TP_fast_assign(
> + __entry->dpaddr = dp;
> + __assign_str(dp_name, ovs_dp_name(dp));
> + __assign_str(dev_name, skb->dev->name);
> + __entry->skbaddr = skb;
> + __entry->len = skb->len;
> + __entry->data_len = skb->data_len;
> + __entry->truesize = skb->truesize;
> + __entry->nr_frags = skb_shinfo(skb)->nr_frags;
> + __entry->gso_size = skb_shinfo(skb)->gso_size;
> + __entry->gso_type = skb_shinfo(skb)->gso_type;
> + __entry->ovs_flow_hash = key->ovs_flow_hash;
> + __entry->recirc_id = key->recirc_id;
> + __entry->keyaddr = key;
> + __entry->key_eth_type = key->eth.type;
> + __entry->key_ct_state = key->ct_state;
> + __entry->key_ct_orig_proto = key->ct_orig_proto;
> + __entry->flow_key_valid = !(key->mac_proto & SW_FLOW_KEY_INVALID);
> + __entry->action_type = nla_type(a);
> + __entry->action_len = nla_len(a);
> + __entry->action_data = nla_data(a);
> + __entry->is_last = nla_is_last(a, rem);
> + ),
> +
> + TP_printk("dpaddr=%p dp_name=%s dev=%s skbaddr=%p len=%u data_len=%u truesize=%u nr_frags=%d
> gso_size=%d gso_type=%#x ovs_flow_hash=0x%08x recirc_id=0x%08x keyaddr=%p eth_type=0x%04x
> ct_state=%02x ct_orig_proto=%02x flow_key_valid=%d action_type=%u action_len=%u action_data=%p
> is_last=%d",
>
> I guess %p will be good enough here, as I see no other trace modules use %px. But I guess, for some of the values
> %*ph might be useful, as it will dump the bytes, i.e., action_data.

The issue with using %*ph for action_data is in the cases where a
netlink attribute doesn't have data. In that case, we don't have any
bytes to print, and I think the behavior would be undefined (see
ct_clear action, or pop_eth action, etc).

> + __entry->dpaddr, __get_str(dp_name), __get_str(dev_name),
> + __entry->skbaddr, __entry->len, __entry->data_len,
> + __entry->truesize, __entry->nr_frags, __entry->gso_size,
> + __entry->gso_type, __entry->ovs_flow_hash,
> + __entry->recirc_id, __entry->keyaddr, __entry->key_eth_type,
> + __entry->key_ct_state, __entry->key_ct_orig_proto,
> + __entry->flow_key_valid,
> + __entry->action_type, __entry->action_len,
> + __entry->action_data, __entry->is_last)
> +);
> +
> +TRACE_EVENT(openvswitch_probe_userspace,
> +
> + TP_PROTO(struct datapath *dp, struct sk_buff *skb,
> + struct sw_flow_key *key,
> + const struct dp_upcall_info *upcall_info),
> +
> + TP_ARGS(dp, skb, key, upcall_info),
> +
> + TP_STRUCT__entry(
> + __field( void *, dpaddr )
> + __string( dp_name, ovs_dp_name(dp) )
> + __string( dev_name, skb->dev->name )
> + __field( void *, skbaddr )
> + __field( unsigned int, len )
> + __field( unsigned int, data_len )
> + __field( unsigned int, truesize )
> + __field( u8, nr_frags )
> + __field( u16, gso_size )
> + __field( u16, gso_type )
> + __field( u32, ovs_flow_hash )
> + __field( u32, recirc_id )
> + __field( void *, keyaddr )
> + __field( u16, key_eth_type )
> + __field( u8, key_ct_state )
> + __field( u8, key_ct_orig_proto )
> + __field( unsigned int, flow_key_valid )
> + __field( u8, upcall_cmd )
> + __field( u32, upcall_port )
> + __field( u16, upcall_mru )
> + ),
> +
> + TP_fast_assign(
> + __entry->dpaddr = dp;
> + __assign_str(dp_name, ovs_dp_name(dp));
> + __assign_str(dev_name, skb->dev->name);
> + __entry->skbaddr = skb;
> + __entry->len = skb->len;
> + __entry->data_len = skb->data_len;
> + __entry->truesize = skb->truesize;
> + __entry->nr_frags = skb_shinfo(skb)->nr_frags;
> + __entry->gso_size = skb_shinfo(skb)->gso_size;
> + __entry->gso_type = skb_shinfo(skb)->gso_type;
> + __entry->ovs_flow_hash = key->ovs_flow_hash;
> + __entry->recirc_id = key->recirc_id;
> + __entry->keyaddr = key;
> + __entry->key_eth_type = key->eth.type;
> + __entry->key_ct_state = key->ct_state;
> + __entry->key_ct_orig_proto = key->ct_orig_proto;
> + __entry->flow_key_valid = !(key->mac_proto & SW_FLOW_KEY_INVALID);
> + __entry->upcall_cmd = upcall_info->cmd;
> + __entry->upcall_port = upcall_info->portid;
> + __entry->upcall_mru = upcall_info->mru;
> + ),
> +
> + TP_printk("dpaddr=%p dp_name=%s dev=%s skbaddr=%p len=%u data_len=%u truesize=%u nr_frags=%d
> gso_size=%d gso_type=%#x ovs_flow_hash=0x%08x recirc_id=0x%08x keyaddr=%p eth_type=0x%04x
> ct_state=%02x ct_orig_proto=%02x flow_key_valid=%d upcall_cmd=%u upcall_port=%u upcall_mru=%u",
>
> See %p comment above.

Same applies.

> + __entry->dpaddr, __get_str(dp_name), __get_str(dev_name),
> + __entry->skbaddr, __entry->len, __entry->data_len,
> + __entry->truesize, __entry->nr_frags, __entry->gso_size,
> + __entry->gso_type, __entry->ovs_flow_hash,
> + __entry->recirc_id, __entry->keyaddr, __entry->key_eth_type,
> + __entry->key_ct_state, __entry->key_ct_orig_proto,
> + __entry->flow_key_valid,
> + __entry->upcall_cmd, __entry->upcall_port,
> + __entry->upcall_mru)
> +);
> +
> +#endif /* _TRACE_OPENVSWITCH_H */
> +
> +/* This part must be outside protection */
> +#undef TRACE_INCLUDE_PATH
> +#define TRACE_INCLUDE_PATH .
> +#undef TRACE_INCLUDE_FILE
> +#define TRACE_INCLUDE_FILE openvswitch_trace
> +#include <trace/define_trace.h>
> --
> 2.31.1