[PULL 07/31] replay: synchronize on every virtual timer callback

[Paolo Bonzini]

From: Pavel Dovgalyuk <Pavel.Dovgaluk@gmail.com>

Sometimes virtual timer callbacks depend on order
of virtual timer processing and warping of virtual clock.
Therefore every callback should be logged to make replay deterministic.
This patch creates a checkpoint before every virtual timer callback.
With these checkpoints virtual timers processing and clock warping
events order is completely deterministic.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Acked-by: Alex Bennée <alex.bennee@linaro.org>

--

v2:
  - remove mutex lock/unlock for virtual clock checkpoint since it is
    not process any asynchronous events (commit 
ca9759c2a92f528f256fef0e3922416f7bb47bf9)
  - bump record/replay log file version
Message-Id: <159012932716.27256.8854065545365559921.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 replay/replay.c   |  2 +-
 util/qemu-timer.c | 32 +++++++++-----------------------
 2 files changed, 10 insertions(+), 24 deletions(-)

diff --git a/replay/replay.c b/replay/replay.c
index 7d93746c73..83ed9e0e24 100644
--- a/replay/replay.c
+++ b/replay/replay.c
@@ -22,7 +22,7 @@
 
 /* Current version of the replay mechanism.
    Increase it when file format changes. */
-#define REPLAY_VERSION              0xe02009
+#define REPLAY_VERSION              0xe0200a
 /* Size of replay log header */
 #define HEADER_SIZE                 (sizeof(uint32_t) + sizeof(uint64_t))
 
diff --git a/util/qemu-timer.c b/util/qemu-timer.c
index b6575a2cd5..f62b4feecd 100644
--- a/util/qemu-timer.c
+++ b/util/qemu-timer.c
@@ -501,7 +501,6 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
     bool progress = false;
     QEMUTimerCB *cb;
     void *opaque;
-    bool need_replay_checkpoint = false;
 
     if (!atomic_read(&timer_list->active_timers)) {
         return false;
@@ -517,16 +516,6 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
         break;
     default:
     case QEMU_CLOCK_VIRTUAL:
-        if (replay_mode != REPLAY_MODE_NONE) {
-            /* Checkpoint for virtual clock is redundant in cases where
-             * it's being triggered with only non-EXTERNAL timers, because
-             * these timers don't change guest state directly.
-             * Since it has conditional dependence on specific timers, it is
-             * subject to race conditions and requires special handling.
-             * See below.
-             */
-            need_replay_checkpoint = true;
-        }
         break;
     case QEMU_CLOCK_HOST:
         if (!replay_checkpoint(CHECKPOINT_CLOCK_HOST)) {
@@ -559,19 +548,16 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
              */
             break;
         }
-        if (need_replay_checkpoint
-                && !(ts->attributes & QEMU_TIMER_ATTR_EXTERNAL)) {
-            /* once we got here, checkpoint clock only once */
-            need_replay_checkpoint = false;
+        /* Checkpoint for virtual clock is redundant in cases where
+         * it's being triggered with only non-EXTERNAL timers, because
+         * these timers don't change guest state directly.
+         */
+        if (replay_mode != REPLAY_MODE_NONE
+            && timer_list->clock->type == QEMU_CLOCK_VIRTUAL
+            && !(ts->attributes & QEMU_TIMER_ATTR_EXTERNAL)
+            && !replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL)) {
             qemu_mutex_unlock(&timer_list->active_timers_lock);
-            if (!replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL)) {
-                goto out;
-            }
-            qemu_mutex_lock(&timer_list->active_timers_lock);
-            /* The lock was released; start over again in case the list was
-             * modified.
-             */
-            continue;
+            goto out;
         }
 
         /* remove timer from the list before calling the callback */
-- 
2.26.2