diff -Nru qemu-2.5+dfsg/debian/changelog qemu-2.5+dfsg/debian/changelog
--- qemu-2.5+dfsg/debian/changelog	2018-12-12 10:18:01.000000000 -0200
+++ qemu-2.5+dfsg/debian/changelog	2019-03-01 15:59:01.000000000 -0300
@@ -1,3 +1,12 @@
+qemu (1:2.5+dfsg-5ubuntu10.35) xenial; urgency=medium
+
+  * Fix deadlock when detaching network interface (LP: #1818880)
+    Fixed by upstream patch:
+    - d/p/lp-1818880-rcu-disable-atfork.patch: rcu: completely disable
+      pthread_atfork callbacks as soon as possible
+
+ -- Heitor R. Alves de Siqueira <halves@canonical.com>  Fri, 01 Mar 2019 15:59:01 -0300
+
 qemu (1:2.5+dfsg-5ubuntu10.34) xenial; urgency=medium
 
   * d/p/ubuntu/lp1807743-linux-user-timerfd.patch: fix define for
diff -Nru qemu-2.5+dfsg/debian/patches/lp-1818880-rcu-disable-atfork.patch qemu-2.5+dfsg/debian/patches/lp-1818880-rcu-disable-atfork.patch
--- qemu-2.5+dfsg/debian/patches/lp-1818880-rcu-disable-atfork.patch	1969-12-31 21:00:00.000000000 -0300
+++ qemu-2.5+dfsg/debian/patches/lp-1818880-rcu-disable-atfork.patch	2019-03-01 15:59:01.000000000 -0300
@@ -0,0 +1,107 @@
+From 73c6e4013b4cd92d3d531bc22cc29e6036ef42e0 Mon Sep 17 00:00:00 2001
+From: Paolo Bonzini <pbonzini@redhat.com>
+Date: Wed, 27 Jan 2016 08:49:21 +0100
+Subject: [PATCH 1/1] rcu: completely disable pthread_atfork callbacks as soon as possible
+
+Because of -daemonize, system mode QEMU sometimes needs to fork() and
+keep RCU enabled in the child.  However, there is a possible deadlock
+with synchronize_rcu:
+
+- the CPU thread is inside a RCU critical section and wants to take
+  the BQL in order to do MMIO
+
+- the monitor thread, which is owning the BQL, calls rcu_init_lock
+  which tries to take the rcu_sync_lock
+
+- the call_rcu thread has taken rcu_sync_lock in synchronize_rcu, but
+  synchronize_rcu needs the CPU thread to end the critical section
+  before returning.
+
+This cannot happen for user-mode emulation, because it does not have
+a BQL.
+
+To fix it, assume that system mode QEMU only forks in preparation for
+exec (except when daemonizing) and disable pthread_atfork as soon as
+the double fork has happened.
+
+Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
+Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
+Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
+
+Origin: upstream, https://git.qemu.org/?p=qemu.git;a=commit;h=73c6e4013b4c
+Bug-Ubuntu: https://bugs.launchpad.net/cloud-archive/+bug/1818880
+---
+ include/qemu/rcu.h |  6 ++++++
+ util/rcu.c         | 20 ++++++++++++++++++++
+ vl.c               |  1 +
+ 3 files changed, 27 insertions(+)
+
+Index: qemu-2.5+dfsg/include/qemu/rcu.h
+===================================================================
+--- qemu-2.5+dfsg.orig/include/qemu/rcu.h
++++ qemu-2.5+dfsg/include/qemu/rcu.h
+@@ -117,6 +117,12 @@ extern void synchronize_rcu(void);
+  */
+ extern void rcu_register_thread(void);
+ extern void rcu_unregister_thread(void);
++
++/*
++ * Support for fork().  fork() support is enabled at startup.
++ */
++extern void rcu_enable_atfork(void);
++extern void rcu_disable_atfork(void);
+ extern void rcu_after_fork(void);
+ 
+ struct rcu_head;
+Index: qemu-2.5+dfsg/util/rcu.c
+===================================================================
+--- qemu-2.5+dfsg.orig/util/rcu.c
++++ qemu-2.5+dfsg/util/rcu.c
+@@ -323,15 +323,35 @@ static void rcu_init_complete(void)
+     rcu_register_thread();
+ }
+ 
++static int atfork_depth = 1;
++
++void rcu_enable_atfork(void)
++{
++    atfork_depth++;
++}
++
++void rcu_disable_atfork(void)
++{
++    atfork_depth--;
++}
++
+ #ifdef CONFIG_POSIX
+ static void rcu_init_lock(void)
+ {
++    if (atfork_depth < 1) {
++        return;
++    }
++
+     qemu_mutex_lock(&rcu_sync_lock);
+     qemu_mutex_lock(&rcu_registry_lock);
+ }
+ 
+ static void rcu_init_unlock(void)
+ {
++    if (atfork_depth < 1) {
++        return;
++    }
++
+     qemu_mutex_unlock(&rcu_registry_lock);
+     qemu_mutex_unlock(&rcu_sync_lock);
+ }
+Index: qemu-2.5+dfsg/vl.c
+===================================================================
+--- qemu-2.5+dfsg.orig/vl.c
++++ qemu-2.5+dfsg/vl.c
+@@ -4046,6 +4046,7 @@ int main(int argc, char **argv, char **e
+     loc_set_none();
+ 
+     os_daemonize();
++    rcu_disable_atfork();
+ 
+     if (qemu_init_main_loop(&main_loop_err)) {
+         error_report_err(main_loop_err);
diff -Nru qemu-2.5+dfsg/debian/patches/series qemu-2.5+dfsg/debian/patches/series
--- qemu-2.5+dfsg/debian/patches/series	2018-12-12 10:18:01.000000000 -0200
+++ qemu-2.5+dfsg/debian/patches/series	2019-03-01 15:59:01.000000000 -0300
@@ -250,3 +250,4 @@
 CVE-2018-19364-1.patch
 CVE-2018-19364-2.patch
 ubuntu/lp1807743-linux-user-timerfd.patch
+lp-1818880-rcu-disable-atfork.patch
--- 
-2.17.1
-