Re: [PATCH v2 08/10] s390x: smp: Wait for sigp completion

Janosch Frank
2020-04-29T09:37:16Z

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On 4/29/20 11:06 AM, David Hildenbrand wrote:
> On 29.04.20 10:57, Janosch Frank wrote:
>> On 4/24/20 1:40 PM, Janosch Frank wrote:
>>> On 4/24/20 12:11 PM, David Hildenbrand wrote:
>>>> On 23.04.20 11:10, Janosch Frank wrote:
>>>>> Sigp orders are not necessarily finished when the processor finished
>>>>> the sigp instruction. We need to poll if the order has been finished
>>>>> before we continue.
>>>>>
>>>>> For (re)start and stop we already use sigp sense running and sigp
>>>>> sense loops. But we still lack completion checks for stop and store
>>>>> status, as well as the cpu resets.
>>>>>
>>>>> Let's add them.
>>>>>
>>>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>>>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>>>>> ---
>>>>> lib/s390x/smp.c | 8 ++++++++
>>>>> lib/s390x/smp.h | 1 +
>>>>> s390x/smp.c | 4 ++++
>>>>> 3 files changed, 13 insertions(+)
>>>>>
>>>>> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
>>>>> index 6ef0335..2555bf4 100644
>>>>> --- a/lib/s390x/smp.c
>>>>> +++ b/lib/s390x/smp.c
>>>>> @@ -154,6 +154,14 @@ int smp_cpu_start(uint16_t addr, struct psw psw)
>>>>> return rc;
>>>>> }
>>>>>
>>>>> +void smp_cpu_wait_for_completion(uint16_t addr)
>>>>> +{
>>>>> + uint32_t status;
>>>>> +
>>>>> + /* Loops when cc == 2, i.e. when the cpu is busy with a sigp order */
>>>>> + sigp_retry(1, SIGP_SENSE, 0, &status);
>>>>> +}
>>>>> +
>>>>> int smp_cpu_destroy(uint16_t addr)
>>>>> {
>>>>> struct cpu *cpu;
>>>>> diff --git a/lib/s390x/smp.h b/lib/s390x/smp.h
>>>>> index ce63a89..a8b98c0 100644
>>>>> --- a/lib/s390x/smp.h
>>>>> +++ b/lib/s390x/smp.h
>>>>> @@ -45,6 +45,7 @@ int smp_cpu_restart(uint16_t addr);
>>>>> int smp_cpu_start(uint16_t addr, struct psw psw);
>>>>> int smp_cpu_stop(uint16_t addr);
>>>>> int smp_cpu_stop_store_status(uint16_t addr);
>>>>> +void smp_cpu_wait_for_completion(uint16_t addr);
>>>>> int smp_cpu_destroy(uint16_t addr);
>>>>> int smp_cpu_setup(uint16_t addr, struct psw psw);
>>>>> void smp_teardown(void);
>>>>> diff --git a/s390x/smp.c b/s390x/smp.c
>>>>> index 7462211..48321f4 100644
>>>>> --- a/s390x/smp.c
>>>>> +++ b/s390x/smp.c
>>>>> @@ -75,6 +75,7 @@ static void test_stop_store_status(void)
>>>>> lc->prefix_sa = 0;
>>>>> lc->grs_sa[15] = 0;
>>>>> smp_cpu_stop_store_status(1);
>>>>> + smp_cpu_wait_for_completion(1);
>>>>> mb();
>>>>> report(lc->prefix_sa == (uint32_t)(uintptr_t)cpu->lowcore, "prefix");
>>>>> report(lc->grs_sa[15], "stack");
>>>>> @@ -85,6 +86,7 @@ static void test_stop_store_status(void)
>>>>> lc->prefix_sa = 0;
>>>>> lc->grs_sa[15] = 0;
>>>>> smp_cpu_stop_store_status(1);
>>>>
>>>> Just curious: Would it make sense to add that inside
>>>> smp_cpu_stop_store_status() instead?
>>>>
>>>
>>> I think so, we also wait for stop and start to finish, so why not for
>>> this order code.
>>>
>>
>> I've moved the waiting into the smp library and now the prefix check for
>> stop and store status fails every so often if executed repeatedly.
>>
>> I've tried making the lc ptr volatile, a print of the prefix before the
>> report seems to fix the issue, a print after the report still shows the
>> issue but according to the print both values are the same.
>>
>> I'm currently at a loss...
>
> Are you missing a barrier() somewhere?
>

Maybe, but the question is where?

There's already one before the report:
smp_cpu_stop_store_status(1);
mb();
report(lc->prefix_sa == (uint32_t)(uintptr_t)cpu->lowcore, "prefix");

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