| Message ID | 20240701161039.80008-1-visitorckw@gmail.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v3] ACPI: processor_idle: Fix invalid comparison with insertion sort for latency | expand |
On Mon, Jul 1, 2024 at 6:10 PM Kuan-Wei Chiu <visitorckw@gmail.com> 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") > 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> > --- > v2 -> v3: > - Remove #include <linux/sort.h> > - Cc @stable > > 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 | 36 ++++++++++++++--------------------- > 1 file changed, 14 insertions(+), 22 deletions(-) > > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c > index bd6a7857ce05..17cc81340b4b 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 +385,21 @@ 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) s/arr/states/ please. > { > - 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; Please add an empty line here (and analogously below). > + 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); And here. > + k = j; > + } > + } > } > > static int acpi_processor_power_verify(struct acpi_processor *pr) > @@ -449,10 +444,7 @@ 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); > --
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index bd6a7857ce05..17cc81340b4b 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 +385,21 @@ 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 +444,7 @@ 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);
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> --- v2 -> v3: - Remove #include <linux/sort.h> - Cc @stable 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 | 36 ++++++++++++++--------------------- 1 file changed, 14 insertions(+), 22 deletions(-)