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

[Uri Lublin]

On 06/21/2013 04:50 PM, Yonit Halperin wrote:
> 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__));

This DEBUG_PRINT should be deleted or marked and postpone to
after pdev->io_sem is released below.

>           }
>           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));