napi_synchronize: waiting for NAPI

Some drivers with shared NAPI need a synchronization barrier.
Also suggested by Benjamin Herrenschmidt for EMAC.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 39dd83b183a9..a5e2dc1f0d98 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -407,6 +407,24 @@ static inline void napi_enable(struct napi_struct *n)
         clear_bit(NAPI_STATE_SCHED, &n->state);
 }
 
+#ifdef CONFIG_SMP
+/**
+ *      napi_synchronize - wait until NAPI is not running
+ *      @n: napi context
+ *
+ * Wait until NAPI is done being scheduled on this context.
+ * Waits till any outstanding processing completes but
+ * does not disable future activations.
+ */
+static inline void napi_synchronize(const struct napi_struct *n)
+{
+        while (test_bit(NAPI_STATE_SCHED, &n->state))
+                msleep(1);
+}
+#else
+# define napi_synchronize(n)    barrier()
+#endif
+
 /*
  *      The DEVICE structure.
  *      Actually, this whole structure is a big mistake.  It mixes I/O