Re: [PATCH v3 105/108] pwm: Ensure a struct pwm has the same lifetime as its pwm_chip

[Gustavo A. R. Silva]

On 11/21/23 07:50, Uwe Kleine-König wrote:

It's required to not free the memory underlying a requested PWM
while a consumer still has a reference to it. While currently a pwm_chip
doesn't life long enough in all cases, linking the struct pwm to the
pwm_chip results in the right lifetime as soon as the pwmchip is living
long enough. This happens with the following commits.

Note this is a breaking change for all pwm drivers that don't use
pwmchip_alloc().

Signed-off-by: Uwe Kleine-König <u.kleine-koe...@pengutronix.de>

Reviewed-by: Gustavo A. R. Silva <gustavo...@kernel.org> # for struct_size() 
and __counted_by()

Thanks for including __counted_by(). :)
--
Gustavo

---
  drivers/pwm/core.c  | 26 ++++++++++----------------
  include/linux/pwm.h |  2 +-
  2 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 15942210aa08..029aa1c69591 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -198,7 +198,7 @@ static bool pwm_ops_check(const struct pwm_chip *chip)

void *pwmchip_priv(struct pwm_chip *chip)

  {
-       return (void *)chip + sizeof(*chip);
+       return (void *)chip + struct_size(chip, pwms, chip->npwm);
  }
  EXPORT_SYMBOL_GPL(pwmchip_priv);

@@ -206,8 +206,9 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, si

  {
        struct pwm_chip *chip;
        size_t alloc_size;
+       unsigned int i;

- alloc_size = size_add(sizeof(*chip), sizeof_priv);

+       alloc_size = size_add(struct_size(chip, pwms, npwm), sizeof_priv);

chip = devm_kzalloc(parent, alloc_size, GFP_KERNEL);

        if (!chip)
@@ -217,6 +218,13 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, 
unsigned int npwm, si
        chip->npwm = npwm;
        chip->uses_pwmchip_alloc = true;

+ for (i = 0; i < chip->npwm; i++) {

+               struct pwm_device *pwm = &chip->pwms[i];
+
+               pwm->chip = chip;
+               pwm->hwpwm = i;
+       }
+
        return chip;
  }
  EXPORT_SYMBOL_GPL(devm_pwmchip_alloc);
@@ -234,7 +242,6 @@ EXPORT_SYMBOL_GPL(devm_pwmchip_alloc);
  int __pwmchip_add(struct pwm_chip *chip, struct module *owner)
  {
        int ret;
-       unsigned i;

if (!chip || !chip->dev || !chip->ops || !chip->npwm)

                return -EINVAL;
@@ -253,26 +260,15 @@ int __pwmchip_add(struct pwm_chip *chip, struct module 
*owner)

chip->owner = owner; - chip->pwms = kcalloc(chip->npwm, sizeof(*chip->pwms), GFP_KERNEL);

-       if (!chip->pwms)
-               return -ENOMEM;
-
        mutex_lock(&pwm_lock);

ret = idr_alloc(&pwmchip_idr, chip, 0, 0, GFP_KERNEL);

        if (ret < 0) {
                mutex_unlock(&pwm_lock);
-               kfree(chip->pwms);
                return ret;
        }

chip->id = ret;

-       for (i = 0; i < chip->npwm; i++) {
-               struct pwm_device *pwm = &chip->pwms[i];
-
-               pwm->chip = chip;
-               pwm->hwpwm = i;
-       }

mutex_unlock(&pwm_lock); @@ -303,8 +299,6 @@ void pwmchip_remove(struct pwm_chip *chip)

        idr_remove(&pwmchip_idr, chip->id);

mutex_unlock(&pwm_lock);

-
-       kfree(chip->pwms);
  }
  EXPORT_SYMBOL_GPL(pwmchip_remove);

diff --git a/include/linux/pwm.h b/include/linux/pwm.h

index b8e70ee01d31..a7294ef1495d 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -302,7 +302,7 @@ struct pwm_chip {

/* only used internally by the PWM framework */

        bool uses_pwmchip_alloc;
-       struct pwm_device *pwms;
+       struct pwm_device pwms[] __counted_by(npwm);
  };

static inline struct device *pwmchip_parent(struct pwm_chip *chip)