[Spice-devel] [qxl-win PATCH 2/2] display: fix deadlock when dbg_level >= 15

[Yonit Halperin]

DebugPrintV first locks print_sem, and then locks io_sem.
async_io, locks io_sem.
In ordr to avoid a deadlock, DebugPrintV MUSTN'T be called when
io_sem is locked.

Also notice, that locking io_sem during DebugPrintV limits our ability
to use the log_port for debugging concurrency problems related to ios.
---
 xddm/display/qxldd.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xddm/display/qxldd.h b/xddm/display/qxldd.h
index 1a1b5d5..362c293 100644
--- a/xddm/display/qxldd.h
+++ b/xddm/display/qxldd.h
@@ -474,6 +474,7 @@ static _inline void async_io(PDev *pdev, asyncable_t op, UCHAR val)
     ULONG64 millis;
 
     if (pdev->use_async) {
+        DEBUG_PRINT((pdev, 3, "%s: start async %d\n", __FUNCTION__, (int)op));
         EngAcquireSemaphore(pdev->io_sem);
         WRITE_PORT_UCHAR(pdev->asyncable[op][ASYNC], val);
         /* Our Interrupt may be taken from us unexpectedly, by a surprise removal.
@@ -482,7 +483,6 @@ static _inline void async_io(PDev *pdev, asyncable_t op, UCHAR val)
          * we get reset. We use EngQueryLocalTime because there is no way to differentiate a return on
          * timeout from a return on event set otherwise. */
         timeout.QuadPart = -INTERRUPT_NOT_PRESENT_TIMEOUT_100NS; // negative  => relative
-        DEBUG_PRINT((pdev, 15, "WAIT_FOR_EVENT %d\n", (int)op));
         EngQueryLocalTime(&start);
         WAIT_FOR_EVENT(pdev, pdev->io_cmd_event, &timeout);
         EngQueryLocalTime(&finish);
@@ -492,7 +492,7 @@ static _inline void async_io(PDev *pdev, asyncable_t op, UCHAR val)
             DEBUG_PRINT((pdev, 0, "%s: timeout reached, disabling async io!\n", __FUNCTION__));
         }
         EngReleaseSemaphore(pdev->io_sem);
-        DEBUG_PRINT((pdev, 3, "finished async %d\n", (int)op));
+        DEBUG_PRINT((pdev, 3, "%s: finished async %d\n", __FUNCTION__, (int)op));
     } else {
         if (pdev->asyncable[op][SYNC] == NULL) {
             DEBUG_PRINT((pdev, 0, "ERROR: trying calling sync io on NULL port %d\n", op));
-- 
1.8.1.4