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Date:      Mon, 15 Oct 2018 10:29:30 +0000 (UTC)
From:      Hans Petter Selasky <hselasky@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r339358 - head/sys/net
Message-ID:  <201810151029.w9FATU8r068148@repo.freebsd.org>
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Author: hselasky
Date: Mon Oct 15 10:29:29 2018
New Revision: 339358
URL: https://svnweb.freebsd.org/changeset/base/339358

Log:
  Fix deadlock when destroying VLANs.
  
  Synchronizing the epoch before freeing the multicast addresses while holding
  the VLAN_XLOCK() might lead to a deadlock. Use deferred freeing of the VLAN
  multicast addresses to resolve deadlock. Backtrace:
  
  Thread1:
  epoch_block_handler_preempt()
  ck_epoch_synchronize_wait()
  epoch_wait_preempt()
  vlan_setmulti()
  vlan_ioctl()
  in6m_release_task()
  gtaskqueue_run_locked()
  gtaskqueue_thread_loop()
  fork_exit()
  fork_trampoline()
  
  Thread2:
  sleepq_switch()
  sleepq_wait()
  _sx_xlock_hard()
  _sx_xlock()
  in6_leavegroup()
  in6_purgeaddr()
  if_purgeaddrs()
  if_detach_internal()
  if_detach()
  vlan_clone_destroy()
  if_clone_destroyif()
  if_clone_destroy()
  ifioctl()
  kern_ioctl()
  sys_ioctl()
  amd64_syscall()
  fast_syscall_common()
  syscall()
  
  Differential revision:	https://reviews.freebsd.org/D17496
  Reviewed by:		slavash, mmacy
  Approved by:		re (kib)
  Sponsored by:		Mellanox Technologies

Modified:
  head/sys/net/if_vlan.c

Modified: head/sys/net/if_vlan.c
==============================================================================
--- head/sys/net/if_vlan.c	Mon Oct 15 10:25:34 2018	(r339357)
+++ head/sys/net/if_vlan.c	Mon Oct 15 10:29:29 2018	(r339358)
@@ -153,6 +153,7 @@ struct ifvlantrunk {
 struct vlan_mc_entry {
 	struct sockaddr_dl		mc_addr;
 	CK_SLIST_ENTRY(vlan_mc_entry)	mc_entries;
+	struct epoch_context		mc_epoch_ctx;
 };
 
 struct	ifvlan {
@@ -317,6 +318,13 @@ VNET_DEFINE_STATIC(struct if_clone *, vlan_cloner);
 #define HASH(n, m)	((((n) >> 8) ^ ((n) >> 4) ^ (n)) & (m))
 
 static void
+vlan_mc_free(struct epoch_context *ctx)
+{
+	struct vlan_mc_entry *mc = __containerof(ctx, struct vlan_mc_entry, mc_epoch_ctx);
+	free(mc, M_VLAN);
+}
+
+static void
 vlan_inithash(struct ifvlantrunk *trunk)
 {
 	int i, n;
@@ -572,8 +580,7 @@ vlan_setmulti(struct ifnet *ifp)
 	while ((mc = CK_SLIST_FIRST(&sc->vlan_mc_listhead)) != NULL) {
 		CK_SLIST_REMOVE_HEAD(&sc->vlan_mc_listhead, mc_entries);
 		(void)if_delmulti(ifp_p, (struct sockaddr *)&mc->mc_addr);
-		NET_EPOCH_WAIT();
-		free(mc, M_VLAN);
+		epoch_call(net_epoch_preempt, &mc->mc_epoch_ctx, vlan_mc_free);
 	}
 
 	/* Now program new ones. */
@@ -1485,8 +1492,7 @@ vlan_unconfig_locked(struct ifnet *ifp, int departing)
 					    error);
 			}
 			CK_SLIST_REMOVE_HEAD(&ifv->vlan_mc_listhead, mc_entries);
-			NET_EPOCH_WAIT();
-			free(mc, M_VLAN);
+			epoch_call(net_epoch_preempt, &mc->mc_epoch_ctx, vlan_mc_free);
 		}
 
 		vlan_setflags(ifp, 0); /* clear special flags on parent */

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