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.
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);