Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

* KVM run_on_cpu fix (Alex)
* atomic usage fixes (Emilio, me)
* hugetlbfs alignment fix (Haozhong)
* CharBackend refactoring (Marc-André)
* test-i386 fixes (me)
* MemoryListener optimizations (me)
* Miscellaneous bugfixes (me)
* iSER support (Roy)
* --version formatting (Thomas)

# gpg: Signature made Mon 24 Oct 2016 14:46:19 BST
# gpg:                using RSA key 0xBFFBD25F78C7AE83
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>"
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>"
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream: (50 commits)
  exec.c: workaround regression caused by alignment change in d2f39ad
  char: remove explicit_be_open from CharDriverState
  char: use common error path in qmp_chardev_add
  char: replace avail_connections
  char: remove unused qemu_chr_fe_event
  char: use an enum for CHR_EVENT
  char: remove unused CHR_EVENT_FOCUS
  char: move fe_open in CharBackend
  char: remove explicit_fe_open, use a set_handlers argument
  char: rename chr_close/chr_free
  char: move front end handlers in CharBackend
  tests: start chardev unit tests
  char: make some qemu_chr_fe skip if no driver
  char: replace qemu_chr_claim/release with qemu_chr_fe_init/deinit
  vhost-user: only initialize queue 0 CharBackend
  char: fold qemu_chr_set_handlers in qemu_chr_fe_set_handlers
  char: use qemu_chr_fe* functions with CharBackend argument
  colo: claim in find_and_check_chardev
  char: rename some frontend functions
  char: remaining switch to CharBackend in frontend
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/util/rcu.c b/util/rcu.c
index bceb3e4720..9adc5e4a36 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -82,14 +82,16 @@ static void wait_for_readers(void)
         /* Instead of using atomic_mb_set for index->waiting, and
          * atomic_mb_read for index->ctr, memory barriers are placed
          * manually since writes to different threads are independent.
-         * atomic_mb_set has a smp_wmb before...
+         * qemu_event_reset has acquire semantics, so no memory barrier
+         * is needed here.
          */
-        smp_wmb();
         QLIST_FOREACH(index, &registry, node) {
             atomic_set(&index->waiting, true);
         }
 
-        /* ... and a smp_mb after.  */
+        /* Here, order the stores to index->waiting before the
+         * loads of index->ctr.
+         */
         smp_mb();
 
         QLIST_FOREACH_SAFE(index, &registry, node, tmp) {
@@ -104,9 +106,6 @@ static void wait_for_readers(void)
             }
         }
 
-        /* atomic_mb_read has smp_rmb after.  */
-        smp_rmb();
-
         if (QLIST_EMPTY(&registry)) {
             break;
         }