On Tue, Jul 16, 2024 at 11:29:41PM +0800, Kuan-Wei Chiu wrote:

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") 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 Tested-by: Julian Sikorski belegdol@gmail.com Cc: All applicable stable@vger.kernel.org Link: https://patch.msgid.link/20240701205639.117194-1-visitorckw@gmail.com Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com (cherry picked from commit 233323f9b9f828cd7cd5145ad811c1990b692542) Signed-off-by: Kuan-Wei Chiu visitorckw@gmail.com

Please ignore this patch. I accidentally sent it to the wrong email. Sorry for any noise.

Resent to: https://lore.kernel.org/all/20240716153031.159989-1-visitorckw@gmail.com/

Thanks, Kuan-Wei

---

drivers/acpi/processor_idle.c | 40 ++++++++++++++--------------------- 1 file changed, 16 insertions(+), 24 deletions(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index 4cb44d80bf52..5289c344de90 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> @@ -385,28 +384,24 @@ static void acpi_processor_power_verify_c3(struct acpi_processor *pr, return; } -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;
• u32 tmp;

• for (i = 1; i < length; i++) {

• if (!states[i].valid)
  

• 	continue;
  

• if (!(x->valid && y->valid))

• return;
  

• tmp = x->latency;
• x->latency = y->latency;
• y->latency = tmp;

• 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) @@ -451,10 +446,7 @@ 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); -- 2.34.1