The em_compute_cost() is going to be re-used in runtime modified EM
code path. Thus, make sure that this common code is safe and won't
try to use the NULL pointer. The former em_compute_cost() didn't have to
care about runtime modification code path. The upcoming changes introduce
such option, but with different callback. Those two paths which use
get_cost() (during first EM registration) or update_power() (during
runtime modification) need to be safely handled in em_compute_costs().
Signed-off-by: Lukasz Luba <[email protected]>
---
kernel/power/energy_model.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
index 7ea882401833..35e07933b34a 100644
--- a/kernel/power/energy_model.c
+++ b/kernel/power/energy_model.c
@@ -116,7 +116,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
for (i = nr_states - 1; i >= 0; i--) {
unsigned long power_res, cost;
- if (flags & EM_PERF_DOMAIN_ARTIFICIAL) {
+ if (flags & EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost) {
ret = cb->get_cost(dev, table[i].frequency, &cost);
if (ret || !cost || cost > EM_MAX_POWER) {
dev_err(dev, "EM: invalid cost %lu %d\n",
--
2.25.1
On Mon, Sep 25, 2023 at 10:11 AM Lukasz Luba <[email protected]> wrote:
>
> The em_compute_cost() is going to be re-used in runtime modified EM
> code path. Thus, make sure that this common code is safe and won't
> try to use the NULL pointer. The former em_compute_cost() didn't have to
> care about runtime modification code path. The upcoming changes introduce
> such option, but with different callback. Those two paths which use
> get_cost() (during first EM registration) or update_power() (during
> runtime modification) need to be safely handled in em_compute_costs().
I would just say something like this:
"Subsequent changes will introduce a case in which cb->get_cost may
not be set in em_compute_costs(), so add a check to ensure that it is
not NULL before attempting to dereference it."
The rest of the changelog is just redundant IMO.
>
> Signed-off-by: Lukasz Luba <[email protected]>
> ---
> kernel/power/energy_model.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index 7ea882401833..35e07933b34a 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -116,7 +116,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
> for (i = nr_states - 1; i >= 0; i--) {
> unsigned long power_res, cost;
>
> - if (flags & EM_PERF_DOMAIN_ARTIFICIAL) {
> + if (flags & EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost) {
> ret = cb->get_cost(dev, table[i].frequency, &cost);
> if (ret || !cost || cost > EM_MAX_POWER) {
> dev_err(dev, "EM: invalid cost %lu %d\n",
> --
> 2.25.1
>
On 9/26/23 19:46, Rafael J. Wysocki wrote:
> On Mon, Sep 25, 2023 at 10:11 AM Lukasz Luba <[email protected]> wrote:
>>
>> The em_compute_cost() is going to be re-used in runtime modified EM
>> code path. Thus, make sure that this common code is safe and won't
>> try to use the NULL pointer. The former em_compute_cost() didn't have to
>> care about runtime modification code path. The upcoming changes introduce
>> such option, but with different callback. Those two paths which use
>> get_cost() (during first EM registration) or update_power() (during
>> runtime modification) need to be safely handled in em_compute_costs().
>
> I would just say something like this:
>
> "Subsequent changes will introduce a case in which cb->get_cost may
> not be set in em_compute_costs(), so add a check to ensure that it is
> not NULL before attempting to dereference it."
>
> The rest of the changelog is just redundant IMO.
>
Make sense, thanks, I'll change that.
On 25/09/2023 10:11, Lukasz Luba wrote:
> The em_compute_cost() is going to be re-used in runtime modified EM
> code path. Thus, make sure that this common code is safe and won't
> try to use the NULL pointer. The former em_compute_cost() didn't have to
> care about runtime modification code path. The upcoming changes introduce
> such option, but with different callback. Those two paths which use
> get_cost() (during first EM registration) or update_power() (during
> runtime modification) need to be safely handled in em_compute_costs().
>
> Signed-off-by: Lukasz Luba <[email protected]>
> ---
> kernel/power/energy_model.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index 7ea882401833..35e07933b34a 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -116,7 +116,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
> for (i = nr_states - 1; i >= 0; i--) {
> unsigned long power_res, cost;
>
> - if (flags & EM_PERF_DOMAIN_ARTIFICIAL) {
> + if (flags & EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost) {
> ret = cb->get_cost(dev, table[i].frequency, &cost);
> if (ret || !cost || cost > EM_MAX_POWER) {
> dev_err(dev, "EM: invalid cost %lu %d\n",
I do believe & operator has lower precedence than && operator, thus the
test is actually:
(flags & (EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost))
but it should be
((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost)
Right ?
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On 10/23/23 19:23, Daniel Lezcano wrote:
> On 25/09/2023 10:11, Lukasz Luba wrote:
>> The em_compute_cost() is going to be re-used in runtime modified EM
>> code path. Thus, make sure that this common code is safe and won't
>> try to use the NULL pointer. The former em_compute_cost() didn't have to
>> care about runtime modification code path. The upcoming changes introduce
>> such option, but with different callback. Those two paths which use
>> get_cost() (during first EM registration) or update_power() (during
>> runtime modification) need to be safely handled in em_compute_costs().
>>
>> Signed-off-by: Lukasz Luba <[email protected]>
>> ---
>> kernel/power/energy_model.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index 7ea882401833..35e07933b34a 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -116,7 +116,7 @@ static int em_compute_costs(struct device *dev,
>> struct em_perf_state *table,
>> for (i = nr_states - 1; i >= 0; i--) {
>> unsigned long power_res, cost;
>> - if (flags & EM_PERF_DOMAIN_ARTIFICIAL) {
>> + if (flags & EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost) {
>> ret = cb->get_cost(dev, table[i].frequency, &cost);
>> if (ret || !cost || cost > EM_MAX_POWER) {
>> dev_err(dev, "EM: invalid cost %lu %d\n",
>
> I do believe & operator has lower precedence than && operator, thus the
> test is actually:
>
> (flags & (EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost))
>
> but it should be
>
> ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost)
>
> Right ?
>
The bitwise '&' is stronger than logical '&&', so the code will
work as in your 2nd example. Although, I will change it and add
parentheses for better reading.
Thanks!