On 2019-01-03 14:23, Janosch Frank wrote:
> 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.
But in that case, you also need to do a sclp_wait_busy() before calling
sclp_mark_busy() in all locations - otherwise the code is also not
thread-safe in its current shape, is it?
Thomas
Attachment:
signature.asc
Description: OpenPGP digital signature
