Rename NET_PICKUP_GIANT() to NET_LOCK_GIANT(), and NET_DROP_GIANT()

to NET_UNLOCK_GIANT().  While they are used in similar ways, the
semantics are quite different -- NET_LOCK_GIANT() and NET_UNLOCK_GIANT()
directly wrap mutex lock and unlock operations, whereas drop/pickup
special case the handling of Giant recursion.  Add a comment saying
as much.

Add NET_ASSERT_GIANT(), which conditionally asserts Giant based
on the value of debug_mpsafenet.

2 files changed, 11 insertions, 5 deletions

diff --git a/sys/netinet/ip_input.c b/sys/netinet/ip_input.c
index 8100a62..b798092 100644
--- a/sys/netinet/ip_input.c
+++ b/sys/netinet/ip_input.c
@@ -936,9 +936,9 @@ DPRINTF(("ip_input: no SP, packet discarded\n"));/*XXX*/
 		*(struct sockaddr_in **)(mtag+1) = args.next_hop;
 		m_tag_prepend(m, mtag);
 	}
-	NET_PICKUP_GIANT();
+	NET_LOCK_GIANT();
 	(*inetsw[ip_protox[ip->ip_p]].pr_input)(m, hlen);
-	NET_DROP_GIANT();
+	NET_UNLOCK_GIANT();
 	return;
 bad:
 	m_freem(m);
diff --git a/sys/sys/mutex.h b/sys/sys/mutex.h
index 05575b5..f86679d 100644
--- a/sys/sys/mutex.h
+++ b/sys/sys/mutex.h
@@ -345,20 +345,26 @@ do {									\
  * input path and protocols that require Giant must collect it
  * on entry.  When 0 Giant is grabbed in the network interface
  * ISR's and in the netisr path and there is no need to grab
- * the Giant lock.
+ * the Giant lock.  Note that, unlike GIANT_PICKUP() and
+ * GIANT_DROP(), these macros directly wrap mutex operations
+ * without special recursion handling.
  *
  * This mechanism is intended as temporary until everything of
  * importance is properly locked.
  */
 extern	int debug_mpsafenet;		/* defined in net/netisr.c */
-#define	NET_PICKUP_GIANT() do {						\
+#define	NET_LOCK_GIANT() do {						\
 	if (debug_mpsafenet)						\
 		mtx_lock(&Giant);					\
 } while (0)
-#define	NET_DROP_GIANT() do {						\
+#define	NET_UNLOCK_GIANT() do {						\
 	if (debug_mpsafenet)						\
 		mtx_unlock(&Giant);					\
 } while (0)
+#define	NET_ASSERT_GIANT() do {						\
+	if (debug_mpsafenet)						\
+		mtx_assert(&Giant, MA_OWNED);				\
+} while (0)
 
 #define	UGAR(rval) do {							\
 	int _val = (rval);						\