Re: [PATCH v4] ACPI: processor_idle: Fix invalid comparison with insertion sort for latency

Mario Limonciello
2024-07-02T13:00:07Z

On 7/2/2024 2:28, Julian Sikorski wrote:
> Am 01.07.24 um 22:56 schrieb Kuan-Wei Chiu:
>> The acpi_cst_latency_cmp comparison function currently used for sorting
>> C-state latencies does not satisfy transitivity, causing incorrect
>> sorting results. Specifically, if there are two valid acpi_processor_cx
>> elements A and B and one invalid element C, it may occur that A < B,
>> A = C, and B = C. Sorting algorithms assume that if A < B and A = C,
>> then C < B, leading to incorrect ordering.
>>
>> Given the small size of the array (<=8), we replace the library sort
>> function with a simple insertion sort that properly ignores invalid
>> elements and sorts valid ones based on latency. This change ensures
>> correct ordering of the C-state latencies.
>>
>> Fixes: 65ea8f2c6e23 ("ACPI: processor idle: Fix up C-state latency if
>> not ordered")
>> Cc: stable@vger.kernel.org
>> Reported-by: Julian Sikorski <belegdol@gmail.com>
>> Closes:
>> https://lore.kernel.org/lkml/70674dc7-5586-4183-8953-8095567e73df@gmail.com/
>> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
>> ---
>> v3 -> v4:
>> - Rename the parameter 'arr' to 'states'.
>> - Add empty lines to enhance readability.
>>
>> Note: I only performed a build test and a simple unit test to ensure
>>        the latency of valid elements is correctly sorted in the randomly
>>        generated data.
>>
>
> Hello,
>
> thanks for the patch. I have tested this applied on top of Fedora 6.9.7
> kernel on my Asus laptop and the message about suspend not reaching the
> deepest state is gone. Thank you.

That's great news.

> I wonder whether this will also fix random S3 suspend issues I have been
> seeing on my 5600x since 6.9 kernel too. I will definitely try.

Does your 5600x also sort C states? You'll see message in the logs. If
so yes it could help. If not; you probably will need to bisect that
separately.

>
> Best regards,
> Julian
>
> Tested-by: Julian Sikorski <belegdol@gmail.com>
>
>>   drivers/acpi/processor_idle.c | 37 +++++++++++++++--------------------
>>   1 file changed, 16 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/acpi/processor_idle.c
>> b/drivers/acpi/processor_idle.c
>> index bd6a7857ce05..831fa4a12159 100644
>> --- a/drivers/acpi/processor_idle.c
>> +++ b/drivers/acpi/processor_idle.c
>> @@ -16,7 +16,6 @@
>>   #include <linux/acpi.h>
>>   #include <linux/dmi.h>
>>   #include <linux/sched.h>       /* need_resched() */
>> -#include <linux/sort.h>
>>   #include <linux/tick.h>
>>   #include <linux/cpuidle.h>
>>   #include <linux/cpu.h>
>> @@ -386,25 +385,24 @@ static void
>> acpi_processor_power_verify_c3(struct acpi_processor *pr,
>>       acpi_write_bit_register(ACPI_BITREG_BUS_MASTER_RLD, 1);
>>   }
>> -static int acpi_cst_latency_cmp(const void *a, const void *b)
>> +static void acpi_cst_latency_sort(struct acpi_processor_cx *states,
>> size_t length)
>>   {
>> -    const struct acpi_processor_cx *x = a, *y = b;
>> +    int i, j, k;
>> -    if (!(x->valid && y->valid))
>> -        return 0;
>> -    if (x->latency > y->latency)
>> -        return 1;
>> -    if (x->latency < y->latency)
>> -        return -1;
>> -    return 0;
>> -}
>> -static void acpi_cst_latency_swap(void *a, void *b, int n)
>> -{
>> -    struct acpi_processor_cx *x = a, *y = b;
>> +    for (i = 1; i < length; i++) {
>> +        if (!states[i].valid)
>> +            continue;
>> -    if (!(x->valid && y->valid))
>> -        return;
>> -    swap(x->latency, y->latency);
>> +        for (j = i - 1, k = i; j >= 0; j--) {
>> +            if (!states[j].valid)
>> +                continue;
>> +
>> +            if (states[j].latency > states[k].latency)
>> +                swap(states[j].latency, states[k].latency);
>> +
>> +            k = j;
>> +        }
>> +    }
>>   }
>>   static int acpi_processor_power_verify(struct acpi_processor *pr)
>> @@ -449,10 +447,7 @@ static int acpi_processor_power_verify(struct
>> acpi_processor *pr)
>>       if (buggy_latency) {
>>           pr_notice("FW issue: working around C-state latencies out of
>> order\n");
>> -        sort(&pr->power.states[1], max_cstate,
>> -             sizeof(struct acpi_processor_cx),
>> -             acpi_cst_latency_cmp,
>> -             acpi_cst_latency_swap);
>> +        acpi_cst_latency_sort(&pr->power.states[1], max_cstate);
>>       }
>>       lapic_timer_propagate_broadcast(pr);
>