hwc: Fix div_by_0 crash in hwcomposer

Inside sw_vsync generation loop, there is a logic error
while reading the vsync_rate. The vsync_rate should be re-read
after user sets the vsync_rate by calling start_sw_vsync
explicitly. This is guaranteed by re-reading it
ONLY after the vsync_cond is signalled.

Change-Id: I2da97e6cb972cc812f789c7f0fd621503679177d

1 files changed, 7 insertions, 1 deletions

diff --git a/hwc/sw_vsync.c b/hwc/sw_vsync.c
index cf24b31..fce6d37 100644
--- a/hwc/sw_vsync.c
+++ b/hwc/sw_vsync.c
@@ -60,10 +60,16 @@ static void *vsync_loop(void *data)
 
     for (;;) {
         pthread_mutex_lock(&vsync_mutex);
-        period = vsync_rate; /* re-read rate */
         while (!vsync_loop_active) {
             pthread_cond_wait(&vsync_cond, &vsync_mutex);
         }
+        /* the vsync_rate should be re-read after
+        * user sets the vsync_rate by calling start_sw_vsync
+        * explicitly. This is guaranteed by re-reading it
+        * after the vsync_cond is signalled.
+        */
+        period = vsync_rate; /* re-read rate */
+
         pthread_mutex_unlock(&vsync_mutex);
 
         clock_gettime(CLOCK_MONOTONIC, &tp);