On 03.01.19 14:15, Thomas Huth wrote:
> On 2019-01-03 14:13, Janosch Frank wrote:
>> On 03.01.19 13:58, Thomas Huth wrote:
>>> On 2019-01-03 11:08, Janosch Frank wrote:
>>>> We need to properly implement interrupt handling for SCLP, because on
>>>> z/VM and LPAR SCLP calls are not synchronous!
>>>>
>>>> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>> [...]
>>>> +
>>>> static void sclp_read_scp_info(ReadInfo *ri, int length)
>>>> {
>>>> unsigned int commands[] = { SCLP_CMDW_READ_SCP_INFO_FORCED,
>>>> SCLP_CMDW_READ_SCP_INFO };
>>>> - int i;
>>>> + int i, cc;
>>>>
>>>> for (i = 0; i < ARRAY_SIZE(commands); i++) {
>>>> memset(&ri->h, 0, sizeof(ri->h));
>>>> ri->h.length = length;
>>>>
>>>> - if (sclp_service_call(commands[i], ri))
>>>> + sclp_mark_busy();
>>>> + cc = sclp_service_call(commands[i], ri);
>>>> + sclp_wait_busy();
>>>
>>> You already do the sclp_wait_busy() in sclp_service_call now, so I think
>>> you don't need the sclp_wait_busy() here anymore?
>>
>> Yeah, that has to go.
>>
>>>
>>> Also, what about moving the sclp_mark_busy() calls to the beginning of
>>> sclp_service_call() instead?
>>
>> Wouldn't that create a race on the data of __sccb and we could end with
>> garbled scb commands?
>
> Since there is a sclp_wait_busy in sclp_service_call already, you can be
> sure that the previous command already finished, can't you?
I mean before calling sclp_service_call.
That's only a problem for smp, but before calling sclp, we prepare the
data in the shared __sccb page and that is currently protected by the
busy mark. If it's not, then two threads could write to __sccb at the
same time and the first that succeeds to call sclp will get a mix of
data of both threads.
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