svn commit: r292604 - head/sys/net

[Bjoern A. Zeeb]

Author: bz
Date: Tue Dec 22 15:03:45 2015
New Revision: 292604
URL: https://svnweb.freebsd.org/changeset/base/292604

Log:
  If vnets are torn down while ifconfig runs an ioctl to say, destroy an
  epair(4), we may hit if_detach_internal() without holding a lock and by
  the time we aquire it the interface might be gone.
  We should not panic() in this case as it is our fault for not holding
  the lock all the way. It is not ideal to return silently without error
  to user space, but other callers will all ignore the return values so
  do not change the entire KPI for little benefit for now.
  The ifp will be dealt with one way or another still.
  
  Sponsored by:		The FreeBSD Foundation
  MFC after:		2 weeks
  Reviewed by:		gnn
  Differential Revision:	https://reviews.freebsd.org/D4529

Modified:
  head/sys/net/if.c

Modified: head/sys/net/if.c
==============================================================================
--- head/sys/net/if.c	Tue Dec 22 15:00:04 2015	(r292603)
+++ head/sys/net/if.c	Tue Dec 22 15:03:45 2015	(r292604)
@@ -173,7 +173,7 @@ static int	if_getgroup(struct ifgroupreq
 static int	if_getgroupmembers(struct ifgroupreq *);
 static void	if_delgroups(struct ifnet *);
 static void	if_attach_internal(struct ifnet *, int, struct if_clone *);
-static void	if_detach_internal(struct ifnet *, int, struct if_clone **);
+static int	if_detach_internal(struct ifnet *, int, struct if_clone **);
 
 #ifdef INET6
 /*
@@ -884,7 +884,7 @@ if_detach(struct ifnet *ifp)
 	CURVNET_RESTORE();
 }
 
-static void
+static int
 if_detach_internal(struct ifnet *ifp, int vmove, struct if_clone **ifcp)
 {
 	struct ifaddr *ifa;
@@ -906,11 +906,19 @@ if_detach_internal(struct ifnet *ifp, in
 #endif
 	IFNET_WUNLOCK();
 	if (!found) {
+		/*
+		 * While we would want to panic here, we cannot
+		 * guarantee that the interface is indeed still on
+		 * the list given we don't hold locks all the way.
+		 */
+		return (ENOENT);
+#if 0
 		if (vmove)
 			panic("%s: ifp=%p not on the ifnet tailq %p",
 			    __func__, ifp, &V_ifnet);
 		else
 			return; /* XXX this should panic as well? */
+#endif
 	}
 
 	/* Check if this is a cloned interface or not. */
@@ -993,6 +1001,8 @@ if_detach_internal(struct ifnet *ifp, in
 			(*dp->dom_ifdetach)(ifp,
 			    ifp->if_afdata[dp->dom_family]);
 	}
+
+	return (0);
 }
 
 #ifdef VIMAGE
@@ -1007,12 +1017,16 @@ void
 if_vmove(struct ifnet *ifp, struct vnet *new_vnet)
 {
 	struct if_clone *ifc;
+	int rc;
 
 	/*
 	 * Detach from current vnet, but preserve LLADDR info, do not
 	 * mark as dead etc. so that the ifnet can be reattached later.
+	 * If we cannot find it, we lost the race to someone else.
 	 */
-	if_detach_internal(ifp, 1, &ifc);
+	rc = if_detach_internal(ifp, 1, &ifc);
+	if (rc != 0)
+		return;
 
 	/*
 	 * Unlink the ifnet from ifindex_table[] in current vnet, and shrink