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

[Yonit Halperin]

On 06/23/2013 06:30 AM, Uri Lublin wrote:
> 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.
>
You are right, and probably we should better lock io_sem before testing 
pdev->use_async...
>>           }
>>           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));
>