devip: dont hold ifc wlock during medium bind/unbind

Wlock()'ing the ifc causes a deadlock with Medium
bind/unbind as the routine can walk /net, while
ndb/dns or ndb/cs are currently blocked enumerating
/net/ipifc/*.

The fix is to have a fake medium, called "unbound",
that is set temporarily during the call of Medium
bind and unbind.

That way, the interface rwlock can be released while
bind/unbind is in progress.

The ipifcunbind() routine will refuse to unbind a
ifc that is currently assigned to the "unbound"
medium, preventing any accidents.

1 files changed, 0 insertions, 10 deletions

diff --git a/sys/src/9/ip/netdevmedium.c b/sys/src/9/ip/netdevmedium.c
index 9e265d19b..f60d43b3a 100644
--- a/sys/src/9/ip/netdevmedium.c
+++ b/sys/src/9/ip/netdevmedium.c
@@ -35,7 +35,6 @@ Medium netdevmedium =
 
 /*
  *  called to bind an IP ifc to a generic network device
- *  called with ifc qlock'd
  */
 static void
 netdevbind(Ipifc *ifc, int argc, char **argv)
@@ -58,9 +57,6 @@ netdevbind(Ipifc *ifc, int argc, char **argv)
 	kproc("netdevread", netdevread, ifc);
 }
 
-/*
- *  called with ifc wlock'd
- */
 static void
 netdevunbind(Ipifc *ifc)
 {
@@ -68,26 +64,20 @@ netdevunbind(Ipifc *ifc)
 
 	while(waserror())
 		;
-
 	/* wait for reader to start */
 	while(er->readp == (void*)-1)
 		tsleep(&up->sleep, return0, 0, 300);
 
 	if(er->readp != nil)
 		postnote(er->readp, 1, "unbind", 0);
-
 	poperror();
 
-	wunlock(ifc);
 	while(waserror())
 		;
-
 	/* wait for reader to die */
 	while(er->readp != nil)
 		tsleep(&up->sleep, return0, 0, 300);
-
 	poperror();
-	wlock(ifc);
 
 	if(er->mchan != nil)
 		cclose(er->mchan);