Re: [PATCH v2 2/4] cxl/region: Prevent device_find_child() from modifying caller's match data

Greg Kroah-Hartman
2024-08-24T05:18:38Z

On Tue, Aug 20, 2024 at 08:59:18AM -0500, Ira Weiny wrote:
> Zijun Hu wrote:
> > From: Zijun Hu <quic_zijuhu@quicinc.com>
> >
> > To prepare for constifying the following old driver core API:
> >
> > struct device *device_find_child(struct device *dev, void *data,
> > int (*match)(struct device *dev, void *data));
> > to new:
> > struct device *device_find_child(struct device *dev, const void *data,
> > int (*match)(struct device *dev, const void *data));
> >
> > The new API does not allow its match function (*match)() to modify
> > caller's match data @*data, but match_free_decoder() as the old API's
> > match function indeed modifies relevant match data, so it is not
> > suitable for the new API any more, fixed by implementing a equivalent
> > cxl_device_find_child() instead of the old API usage.
>
> Generally it seems ok but I think some name changes will make this more
> clear. See below.
>
> Also for those working on CXL I'm questioning the use of ID here and the
> dependence on the id's being added to the parent in order. Is that a
> guarantee?
>
> >
> > Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
> > ---
> > drivers/cxl/core/region.c | 36 +++++++++++++++++++++++++++++++++++-
> > 1 file changed, 35 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index 21ad5f242875..8d8f0637f7ac 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -134,6 +134,39 @@ static const struct attribute_group *get_cxl_region_access1_group(void)
> > return &cxl_region_access1_coordinate_group;
> > }
> >
> > +struct cxl_dfc_data {
>
> struct cxld_match_data
>
> 'cxld' == cxl decoder in our world.
>
> > + int (*match)(struct device *dev, void *data);
> > + void *data;
> > + struct device *target_device;
> > +};
> > +
> > +static int cxl_dfc_match_modify(struct device *dev, void *data)
>
> Why not just put this logic into match_free_decoder?
>
> > +{
> > + struct cxl_dfc_data *dfc_data = data;
> > + int res;
> > +
> > + res = dfc_data->match(dev, dfc_data->data);
> > + if (res && get_device(dev)) {
> > + dfc_data->target_device = dev;
> > + return res;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +/*
> > + * I have the same function as device_find_child() but allow to modify
> > + * caller's match data @*data.
> > + */
>
> No need for this comment after the new API is established.
>
> > +static struct device *cxl_device_find_child(struct device *parent, void *data,
> > + int (*match)(struct device *dev, void *data))
> > +{
> > + struct cxl_dfc_data dfc_data = {match, data, NULL};
> > +
> > + device_for_each_child(parent, &dfc_data, cxl_dfc_match_modify);
> > + return dfc_data.target_device;
> > +}
> > +
> > static ssize_t uuid_show(struct device *dev, struct device_attribute *attr,
> > char *buf)
> > {
> > @@ -849,7 +882,8 @@ cxl_region_find_decoder(struct cxl_port *port,
> > dev = device_find_child(&port->dev, &cxlr->params,
> > match_auto_decoder);
> > else
> > - dev = device_find_child(&port->dev, &id, match_free_decoder);
> > + dev = cxl_device_find_child(&port->dev, &id,
> > + match_free_decoder);
>
> This is too literal. How about the following (passes basic cxl-tests).
>
> Ira
>
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 21ad5f242875..c1e46254efb8 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -794,10 +794,15 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
> return rc;
> }
>
> +struct cxld_match_data {
> + int id;
> + struct device *target_device;
> +};
> +
> static int match_free_decoder(struct device *dev, void *data)
> {
> + struct cxld_match_data *match_data = data;
> struct cxl_decoder *cxld;
> - int *id = data;
>
> if (!is_switch_decoder(dev))
> return 0;
> @@ -805,17 +810,30 @@ static int match_free_decoder(struct device *dev, void *data)
> cxld = to_cxl_decoder(dev);
>
> /* enforce ordered allocation */
> - if (cxld->id != *id)
> + if (cxld->id != match_data->id)
> return 0;
>
> - if (!cxld->region)
> + if (!cxld->region && get_device(dev)) {
> + match_data->target_device = dev;
> return 1;
> + }
>
> - (*id)++;
> + match_data->id++;
>
> return 0;
> }
>
> +static struct device *find_free_decoder(struct device *parent)
> +{
> + struct cxld_match_data match_data = {
> + .id = 0,
> + .target_device = NULL,
> + };
> +
> + device_for_each_child(parent, &match_data, match_free_decoder);
> + return match_data.target_device;
> +}

I like this type of re-write much better, thanks!

greg k-h