On 6/30/2024 23:42, 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@xxxxxxxxx>
Closes: https://lore.kernel.org/lkml/70674dc7-5586-4183-8953-8095567e73df@xxxxxxxxx/
Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
---
v1 -> v2:
- Avoid swapping if arr[i] is an invalid element.
I do not have the appropriate AMD hardware to reproduce this issue and
test the patch.
Even if you had hardware, the behavior stems from a BIOS bug with the
_CST entries. I know it's been fixed in the BIOS on most platforms in
that era, but if I recall correctly from a few years back Julian's
system was EoL already.
However, if the aforementioned reason is indeed the
source of the problem, I believe this patch might help.
Thanks!
Assuming this patch works for Julian, I believe you can also drop the
#include <linux/sort.h>
from this file as well.
I do think this should be cc to @stable too in that case.
drivers/acpi/processor_idle.c | 35 ++++++++++++++---------------------
1 file changed, 14 insertions(+), 21 deletions(-)
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index bd6a7857ce05..813c718b9108 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -386,25 +386,21 @@ 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 *arr, 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;
-
- if (!(x->valid && y->valid))
- return;
- swap(x->latency, y->latency);
+ for (i = 1; i < length; i++) {
+ if (!arr[i].valid)
+ continue;
+ for (j = i - 1, k = i; j >= 0; j--) {
+ if (!arr[j].valid)
+ continue;
+ if (arr[j].latency > arr[k].latency)
+ swap(arr[j].latency, arr[k].latency);
+ k = j;
+ }
+ }
}
static int acpi_processor_power_verify(struct acpi_processor *pr)
@@ -449,10 +445,7 @@ 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);
