datapath: Enable RT Kernel supportHEADmaster

I found these files where there can be some issues on RT kernel:
- datapath/datapath.c
- datapath/vport.c
- datapath/linux/compat/workqueue.c

Important calls here are (that doesn't fit well with RT are):
- spin_lock_irq{save}()
- spin_lock_bh()
- local_bh_disable()

1- spin_lock_irq{save}()

These are simply converted to spin_lock() in RT and so access to critical
sections is guaranteed to be serialized.. And so nothing is required to be fixed
for it..

2- spin_lock_bh()

It guarantees code to be serialized and hence shouldn't be a problem..

2- local_bh_disable()

This is how it is implemented:

	+void local_bh_disable(void)
	+{
	+       migrate_disable();
	+       current->softirq_nestcnt++;
	+}
	+EXPORT_SYMBOL(local_bh_disable);

And here is the problem: Code currently using local_bh_disable() isn't
guaranteed to be serialized and so that is required to be fixed.

A simple solution would be to add a spin_lock_bh() for this case which will make
it work (efficiently) for both RT and non-RT cases.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

2 files changed, 5 insertions, 2 deletions

diff --git a/datapath/actions.c b/datapath/actions.c
index 30ea1d23..3550a00a 100644
--- a/datapath/actions.c
+++ b/datapath/actions.c
@@ -28,6 +28,7 @@
 #include <linux/in6.h>
 #include <linux/if_arp.h>
 #include <linux/if_vlan.h>
+#include <linux/spinlock.h>
 #include <net/ip.h>
 #include <net/ipv6.h>
 #include <net/checksum.h>
@@ -38,6 +39,8 @@
 #include "vlan.h"
 #include "vport.h"
 
+static DEFINE_SPINLOCK(action_lock);
+
 static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			      const struct nlattr *attr, int len, bool keep_skb);
 
@@ -600,6 +603,7 @@ int ovs_execute_actions(struct datapath *dp, struct sk_buff *skb)
 	int error;
 
 	/* Check whether we've looped too much. */
+	spin_lock_bh(&action_lock);
 	loop = &__get_cpu_var(loop_counters);
 	if (unlikely(++loop->count > MAX_LOOPS))
 		loop->looping = true;
@@ -622,5 +626,6 @@ out_loop:
 	if (!--loop->count)
 		loop->looping = false;
 
+	spin_unlock_bh(&action_lock);
 	return error;
 }
diff --git a/datapath/datapath.c b/datapath/datapath.c
index 50ee6cd3..6b7298a6 100644
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -528,9 +528,7 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
 	if (!dp)
 		goto err_unlock;
 
-	local_bh_disable();
 	err = ovs_execute_actions(dp, packet);
-	local_bh_enable();
 	rcu_read_unlock();
 
 	ovs_flow_free(flow, false);