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Message-ID: <20250430124758.1159480-12-bigeasy@linutronix.de>
Date: Wed, 30 Apr 2025 14:47:51 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: netdev@...r.kernel.org,
linux-rt-devel@...ts.linux.dev
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Aaron Conole <aconole@...hat.com>,
Eelco Chaudron <echaudro@...hat.com>,
Ilya Maximets <i.maximets@....org>,
dev@...nvswitch.org
Subject: [PATCH net-next v3 11/18] openvswitch: Use nested-BH locking for ovs_pcpu_storage
ovs_pcpu_storage is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
this data structure requires explicit locking.
The data structure can be referenced recursive and there is a recursion
counter to avoid too many recursions.
Add a local_lock_t to the data structure and use
local_lock_nested_bh() for locking. Add an owner of the struct which is
the current task and acquire the lock only if the structure is not owned
by the current task.
Cc: Aaron Conole <aconole@...hat.com>
Cc: Eelco Chaudron <echaudro@...hat.com>
Cc: Ilya Maximets <i.maximets@....org>
Cc: dev@...nvswitch.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
net/openvswitch/actions.c | 31 ++-----------------------------
net/openvswitch/datapath.c | 24 ++++++++++++++++++++++++
net/openvswitch/datapath.h | 33 +++++++++++++++++++++++++++++++++
3 files changed, 59 insertions(+), 29 deletions(-)
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index bebaf16ba8af6..f4996c11aefac 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -39,15 +39,6 @@
#include "flow_netlink.h"
#include "openvswitch_trace.h"
-struct deferred_action {
- struct sk_buff *skb;
- const struct nlattr *actions;
- int actions_len;
-
- /* Store pkt_key clone when creating deferred action. */
- struct sw_flow_key pkt_key;
-};
-
#define MAX_L2_LEN (VLAN_ETH_HLEN + 3 * MPLS_HLEN)
struct ovs_frag_data {
unsigned long dst;
@@ -64,28 +55,10 @@ struct ovs_frag_data {
static DEFINE_PER_CPU(struct ovs_frag_data, ovs_frag_data_storage);
-#define DEFERRED_ACTION_FIFO_SIZE 10
-#define OVS_RECURSION_LIMIT 5
-#define OVS_DEFERRED_ACTION_THRESHOLD (OVS_RECURSION_LIMIT - 2)
-struct action_fifo {
- int head;
- int tail;
- /* Deferred action fifo queue storage. */
- struct deferred_action fifo[DEFERRED_ACTION_FIFO_SIZE];
+DEFINE_PER_CPU(struct ovs_pcpu_storage, ovs_pcpu_storage) = {
+ .bh_lock = INIT_LOCAL_LOCK(bh_lock),
};
-struct action_flow_keys {
- struct sw_flow_key key[OVS_DEFERRED_ACTION_THRESHOLD];
-};
-
-struct ovs_pcpu_storage {
- struct action_fifo action_fifos;
- struct action_flow_keys flow_keys;
- int exec_level;
-};
-
-static DEFINE_PER_CPU(struct ovs_pcpu_storage, ovs_pcpu_storage);
-
/* Make a clone of the 'key', using the pre-allocated percpu 'flow_keys'
* space. Return NULL if out of key spaces.
*/
diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index aaa6277bb49c2..b8f766978466d 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -244,11 +244,13 @@ void ovs_dp_detach_port(struct vport *p)
/* Must be called with rcu_read_lock. */
void ovs_dp_process_packet(struct sk_buff *skb, struct sw_flow_key *key)
{
+ struct ovs_pcpu_storage *ovs_pcpu = this_cpu_ptr(&ovs_pcpu_storage);
const struct vport *p = OVS_CB(skb)->input_vport;
struct datapath *dp = p->dp;
struct sw_flow *flow;
struct sw_flow_actions *sf_acts;
struct dp_stats_percpu *stats;
+ bool ovs_pcpu_locked = false;
u64 *stats_counter;
u32 n_mask_hit;
u32 n_cache_hit;
@@ -290,10 +292,26 @@ void ovs_dp_process_packet(struct sk_buff *skb, struct sw_flow_key *key)
ovs_flow_stats_update(flow, key->tp.flags, skb);
sf_acts = rcu_dereference(flow->sf_acts);
+ /* This path can be invoked recursively: Use the current task to
+ * identify recursive invocation - the lock must be acquired only once.
+ * Even with disabled bottom halves this can be preempted on PREEMPT_RT.
+ * Limit the provecc to RT to avoid assigning `owner' if it can be
+ * avoided.
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && ovs_pcpu->owner != current) {
+ local_lock_nested_bh(&ovs_pcpu_storage.bh_lock);
+ ovs_pcpu->owner = current;
+ ovs_pcpu_locked = true;
+ }
+
error = ovs_execute_actions(dp, skb, sf_acts, key);
if (unlikely(error))
net_dbg_ratelimited("ovs: action execution error on datapath %s: %d\n",
ovs_dp_name(dp), error);
+ if (ovs_pcpu_locked) {
+ ovs_pcpu->owner = NULL;
+ local_unlock_nested_bh(&ovs_pcpu_storage.bh_lock);
+ }
stats_counter = &stats->n_hit;
@@ -671,7 +689,13 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
sf_acts = rcu_dereference(flow->sf_acts);
local_bh_disable();
+ local_lock_nested_bh(&ovs_pcpu_storage.bh_lock);
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ this_cpu_write(ovs_pcpu_storage.owner, current);
err = ovs_execute_actions(dp, packet, sf_acts, &flow->key);
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ this_cpu_write(ovs_pcpu_storage.owner, NULL);
+ local_unlock_nested_bh(&ovs_pcpu_storage.bh_lock);
local_bh_enable();
rcu_read_unlock();
diff --git a/net/openvswitch/datapath.h b/net/openvswitch/datapath.h
index a126407926058..4a665c3cfa906 100644
--- a/net/openvswitch/datapath.h
+++ b/net/openvswitch/datapath.h
@@ -173,6 +173,39 @@ struct ovs_net {
bool xt_label;
};
+struct deferred_action {
+ struct sk_buff *skb;
+ const struct nlattr *actions;
+ int actions_len;
+
+ /* Store pkt_key clone when creating deferred action. */
+ struct sw_flow_key pkt_key;
+};
+
+#define DEFERRED_ACTION_FIFO_SIZE 10
+#define OVS_RECURSION_LIMIT 5
+#define OVS_DEFERRED_ACTION_THRESHOLD (OVS_RECURSION_LIMIT - 2)
+
+struct action_fifo {
+ int head;
+ int tail;
+ /* Deferred action fifo queue storage. */
+ struct deferred_action fifo[DEFERRED_ACTION_FIFO_SIZE];
+};
+
+struct action_flow_keys {
+ struct sw_flow_key key[OVS_DEFERRED_ACTION_THRESHOLD];
+};
+
+struct ovs_pcpu_storage {
+ struct action_fifo action_fifos;
+ struct action_flow_keys flow_keys;
+ int exec_level;
+ struct task_struct *owner;
+ local_lock_t bh_lock;
+};
+DECLARE_PER_CPU(struct ovs_pcpu_storage, ovs_pcpu_storage);
+
/**
* enum ovs_pkt_hash_types - hash info to include with a packet
* to send to userspace.
--
2.49.0
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