Avoid a potential swapsPending underflow by incrementing it before
ScheduleSwap, which may complete it immediately.  And be sure to
decrement it again in case the schedule failed.

Reported-by: Mario Kleiner <[email protected]>
Signed-off-by: Jesse Barnes <[email protected]>
---
 hw/xfree86/dri2/dri2.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/hw/xfree86/dri2/dri2.c b/hw/xfree86/dri2/dri2.c
index 3fc7f4e..8a67122 100644
--- a/hw/xfree86/dri2/dri2.c
+++ b/hw/xfree86/dri2/dri2.c
@@ -654,15 +654,16 @@ DRI2SwapBuffers(ClientPtr client, DrawablePtr pDraw, 
CARD64 target_msc,
        *swap_target = target_msc;
     }
 
+    pPriv->swapsPending++;
     ret = (*ds->ScheduleSwap)(client, pDraw, pDestBuffer, pSrcBuffer,
                              swap_target, divisor, remainder, func, data);
     if (!ret) {
+       pPriv->swapsPending--; /* didn't schedule */
         xf86DrvMsg(pScreen->myNum, X_ERROR,
                   "[DRI2] %s: driver failed to schedule swap\n", __func__);
        return BadDrawable;
     }
 
-    pPriv->swapsPending++;
     pPriv->last_swap_target = *swap_target;
 
     /* According to spec, return expected swapbuffers count SBC after this swap
-- 
1.6.6.1

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