| Message ID | 20230612165302.1.I24b838a5b4151fb32bccd6f36397998ea2df9fbb@changeid (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/bridge: ti-sn65dsi86: Fix auxiliary bus lifetime | expand |
Quoting Douglas Anderson (2023-06-12 16:53:03) > Memory for the "struct device" for any given device isn't supposed to > be released until the device's release() is called. This is important > because someone might be holding a kobject reference to the "struct > device" and might try to access one of its members even after any > other cleanup/uninitialization has happened. > > Code analysis of ti-sn65dsi86 shows that this isn't quite right. When > the code was written, it was believed that we could rely on the fact > that the child devices would all be freed before the parent devices > and thus we didn't need to worry about a release() function. While I > still believe that the parent's "struct device" is guaranteed to > outlive the child's "struct device" (because the child holds a kobject > reference to the parent), the parent's "devm" allocated memory is a > different story. That appears to be freed much earlier. > > Let's make this better for ti-sn65dsi86 by allocating each auxiliary > with kzalloc and then free that memory in the release(). > > Fixes: bf73537f411b ("drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers") > Suggested-by: Stephen Boyd <swboyd@chromium.org> > Signed-off-by: Douglas Anderson <dianders@chromium.org> > --- Thanks! > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > index 597ceb7024e0..db1461cc3170 100644 > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > @@ -464,27 +464,32 @@ static void ti_sn65dsi86_delete_aux(void *data) > auxiliary_device_delete(data); > } > > -/* > - * AUX bus docs say that a non-NULL release is mandatory, but it makes no > - * sense for the model used here where all of the aux devices are allocated > - * in the single shared structure. We'll use this noop as a workaround. > - */ > -static void ti_sn65dsi86_noop(struct device *dev) {} > +static void ti_sn65dsi86_aux_device_release(struct device *dev) > +{ > + struct auxiliary_device *aux = container_of(dev, struct auxiliary_device, dev); > + > + kfree(aux); > +} > > static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata, > - struct auxiliary_device *aux, > + struct auxiliary_device **aux_out, > const char *name) > { > struct device *dev = pdata->dev; > + struct auxiliary_device *aux; > int ret; > > + aux = kzalloc(sizeof(*aux), GFP_KERNEL); Check for allocation failure? > + > aux->name = name; > aux->dev.parent = dev; > - aux->dev.release = ti_sn65dsi86_noop; > + aux->dev.release = ti_sn65dsi86_aux_device_release; > device_set_of_node_from_dev(&aux->dev, dev); > ret = auxiliary_device_init(aux); > - if (ret) > + if (ret) { > + kfree(aux); > return ret; > + } > ret = devm_add_action_or_reset(dev, ti_sn65dsi86_uninit_aux, aux); > if (ret) > return ret; > @@ -494,6 +499,9 @@ static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata, > return ret; > ret = devm_add_action_or_reset(dev, ti_sn65dsi86_delete_aux, aux); > Nitpick: Stick this if line to the line above > + if (!ret) > + *aux_out = aux; > + > return ret;
diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c index 597ceb7024e0..db1461cc3170 100644 --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c @@ -170,10 +170,10 @@ * @pwm_refclk_freq: Cache for the reference clock input to the PWM. */ struct ti_sn65dsi86 { - struct auxiliary_device bridge_aux; - struct auxiliary_device gpio_aux; - struct auxiliary_device aux_aux; - struct auxiliary_device pwm_aux; + struct auxiliary_device *bridge_aux; + struct auxiliary_device *gpio_aux; + struct auxiliary_device *aux_aux; + struct auxiliary_device *pwm_aux; struct device *dev; struct regmap *regmap; @@ -464,27 +464,32 @@ static void ti_sn65dsi86_delete_aux(void *data) auxiliary_device_delete(data); } -/* - * AUX bus docs say that a non-NULL release is mandatory, but it makes no - * sense for the model used here where all of the aux devices are allocated - * in the single shared structure. We'll use this noop as a workaround. - */ -static void ti_sn65dsi86_noop(struct device *dev) {} +static void ti_sn65dsi86_aux_device_release(struct device *dev) +{ + struct auxiliary_device *aux = container_of(dev, struct auxiliary_device, dev); + + kfree(aux); +} static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata, - struct auxiliary_device *aux, + struct auxiliary_device **aux_out, const char *name) { struct device *dev = pdata->dev; + struct auxiliary_device *aux; int ret; + aux = kzalloc(sizeof(*aux), GFP_KERNEL); + aux->name = name; aux->dev.parent = dev; - aux->dev.release = ti_sn65dsi86_noop; + aux->dev.release = ti_sn65dsi86_aux_device_release; device_set_of_node_from_dev(&aux->dev, dev); ret = auxiliary_device_init(aux); - if (ret) + if (ret) { + kfree(aux); return ret; + } ret = devm_add_action_or_reset(dev, ti_sn65dsi86_uninit_aux, aux); if (ret) return ret; @@ -494,6 +499,9 @@ static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata, return ret; ret = devm_add_action_or_reset(dev, ti_sn65dsi86_delete_aux, aux); + if (!ret) + *aux_out = aux; + return ret; }
Memory for the "struct device" for any given device isn't supposed to be released until the device's release() is called. This is important because someone might be holding a kobject reference to the "struct device" and might try to access one of its members even after any other cleanup/uninitialization has happened. Code analysis of ti-sn65dsi86 shows that this isn't quite right. When the code was written, it was believed that we could rely on the fact that the child devices would all be freed before the parent devices and thus we didn't need to worry about a release() function. While I still believe that the parent's "struct device" is guaranteed to outlive the child's "struct device" (because the child holds a kobject reference to the parent), the parent's "devm" allocated memory is a different story. That appears to be freed much earlier. Let's make this better for ti-sn65dsi86 by allocating each auxiliary with kzalloc and then free that memory in the release(). Fixes: bf73537f411b ("drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers") Suggested-by: Stephen Boyd <swboyd@chromium.org> Signed-off-by: Douglas Anderson <dianders@chromium.org> --- drivers/gpu/drm/bridge/ti-sn65dsi86.c | 34 +++++++++++++++++---------- 1 file changed, 21 insertions(+), 13 deletions(-)