Rework global locks for interface list and index management, correcting

several critical bugs, including race conditions and lock order issues:

Replace the single rwlock, ifnet_lock, with two locks, an rwlock and an
sxlock.  Either can be held to stablize the lists and indexes, but both
are required to write.  This allows the list to be held stable in both
network interrupt contexts and sleepable user threads across sleeping
memory allocations or device driver interactions.  As before, writes to
the interface list must occur from sleepable contexts.

Reviewed by:	bz, julian
MFC after:	3 days

1 files changed, 34 insertions, 8 deletions

diff --git a/sys/net/if_var.h b/sys/net/if_var.h
index aa83161..0bfd9f1 100644
--- a/sys/net/if_var.h
+++ b/sys/net/if_var.h
@@ -85,6 +85,7 @@ struct	vnet;
 #include <sys/lock.h>		/* XXX */
 #include <sys/mutex.h>		/* XXX */
 #include <sys/rwlock.h>		/* XXX */
+#include <sys/sx.h>		/* XXX */
 #include <sys/event.h>		/* XXX */
 #include <sys/_task.h>
 
@@ -754,14 +755,39 @@ struct ifmultiaddr {
 
 #ifdef _KERNEL
 
-extern	struct rwlock ifnet_lock;
-#define	IFNET_LOCK_INIT() \
-   rw_init_flags(&ifnet_lock, "ifnet",  RW_RECURSE)
-#define	IFNET_WLOCK()		rw_wlock(&ifnet_lock)
-#define	IFNET_WUNLOCK()		rw_wunlock(&ifnet_lock)
-#define	IFNET_WLOCK_ASSERT()	rw_assert(&ifnet_lock, RA_LOCKED)
-#define	IFNET_RLOCK()		rw_rlock(&ifnet_lock)
-#define	IFNET_RUNLOCK()		rw_runlock(&ifnet_lock)	
+extern	struct rwlock ifnet_rwlock;
+extern	struct sx ifnet_sxlock;
+
+#define	IFNET_LOCK_INIT() do {						\
+	rw_init_flags(&ifnet_rwlock, "ifnet_rw",  RW_RECURSE);		\
+	sx_init_flags(&ifnet_sxlock, "ifnet_sx",  SX_RECURSE);		\
+} while(0)
+
+#define	IFNET_WLOCK() do {						\
+	sx_xlock(&ifnet_sxlock);					\
+	rw_wlock(&ifnet_rwlock);					\
+} while (0)
+
+#define	IFNET_WUNLOCK() do {						\
+	rw_wunlock(&ifnet_rwlock);					\
+	sx_xunlock(&ifnet_sxlock);					\
+} while (0)
+
+/*
+ * To assert the ifnet lock, you must know not only whether it's for read or
+ * write, but also whether it was acquired with sleep support or not.
+ */
+#define	IFNET_RLOCK_ASSERT()		sx_assert(&ifnet_sxlock, SA_SLOCKED)
+#define	IFNET_RLOCK_NOSLEEP_ASSERT()	rw_assert(&ifnet_rwlock, RA_RLOCKED)
+#define	IFNET_WLOCK_ASSERT() do {					\
+	sx_assert(&ifnet_sxlock, SA_XLOCKED);				\
+	rw_assert(&ifnet_rwlock, RA_WLOCKED);				\
+} while (0)
+
+#define	IFNET_RLOCK()		sx_slock(&ifnet_sxlock)
+#define	IFNET_RLOCK_NOSLEEP()	rw_rlock(&ifnet_rwlock)
+#define	IFNET_RUNLOCK()		sx_sunlock(&ifnet_sxlock)
+#define	IFNET_RUNLOCK_NOSLEEP()	rw_runlock(&ifnet_rwlock)
 
 /*
  * Look up an ifnet given its index; the _ref variant also acquires a