net: napi: use READ_ONCE()/WRITE_ONCE()

gro_flush_timeout and napi_defer_hard_irqs can be read
from napi_complete_done() while other cpus write the value,
whithout explicit synchronization.

Use READ_ONCE()/WRITE_ONCE() to annotate the races.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -6242,12 +6242,12 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 
 	if (work_done) {
 		if (n->gro_bitmask)
-			timeout = n->dev->gro_flush_timeout;
-		n->defer_hard_irqs_count = n->dev->napi_defer_hard_irqs;
+			timeout = READ_ONCE(n->dev->gro_flush_timeout);
+		n->defer_hard_irqs_count = READ_ONCE(n->dev->napi_defer_hard_irqs);
 	}
 	if (n->defer_hard_irqs_count > 0) {
 		n->defer_hard_irqs_count--;
-		timeout = n->dev->gro_flush_timeout;
+		timeout = READ_ONCE(n->dev->gro_flush_timeout);
 		if (timeout)
 			ret = false;
 	}

net/core/net-sysfs.c

@@ -367,7 +367,7 @@ NETDEVICE_SHOW_RW(tx_queue_len, fmt_dec);
 
 static int change_gro_flush_timeout(struct net_device *dev, unsigned long val)
 {
-	dev->gro_flush_timeout = val;
+	WRITE_ONCE(dev->gro_flush_timeout, val);
 	return 0;
 }
 
@@ -384,7 +384,7 @@ NETDEVICE_SHOW_RW(gro_flush_timeout, fmt_ulong);
 
 static int change_napi_defer_hard_irqs(struct net_device *dev, unsigned long val)
 {
-	dev->napi_defer_hard_irqs = val;
+	WRITE_ONCE(dev->napi_defer_hard_irqs, val);
 	return 0;
 }