| Message ID | 20230925081139.1305766-7-lukasz.luba@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Introduce runtime modifiable Energy Model | expand |
On Mon, Sep 25, 2023 at 10:11 AM Lukasz Luba <lukasz.luba@arm.com> 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 <lukasz.luba@arm.com> > --- > 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 <lukasz.luba@arm.com> 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 <lukasz.luba@arm.com> > --- > 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 ?
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 <lukasz.luba@arm.com> >> --- >> 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!
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",
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 <lukasz.luba@arm.com> --- kernel/power/energy_model.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)