linux-kernel - Re: [PATCH v2 1/1] device property: Allow error pointer to be passed to fwnode APIs

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Date:   Sat, 05 Mar 2022 13:46:56 +0100
From:   Nuno Sá <noname.nuno@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Nuno Sá <nuno.sa@...log.com>
Subject: Re: [PATCH v2 1/1] device property: Allow error pointer to be
 passed to fwnode APIs

On Fri, 2022-03-04 at 19:32 +0200, Andy Shevchenko wrote:
> Some of the fwnode APIs might return an error pointer instead of NULL
> or valid fwnode handle. The result of such API call may be considered
> optional and hence the test for it is usually done in a form of
> 
>         fwnode = fwnode_find_reference(...);
>         if (IS_ERR_OR_NULL(fwnode))
>                 ...error handling...
> 
> Nevertheless the resulting fwnode may have bumped reference count and
> hence caller of the above API is obliged to call fwnode_handle_put().
> Since fwnode may be not valid either as NULL or error pointer the
> check
> has to be performed there. This approach uglifies the code and adds
> a point of making a mistake, i.e. forgetting about error point case.
> 
> To prevent this allow error pointer to be passed to the fwnode APIs.
> 
> Fixes: 83b34afb6b79 ("device property: Introduce
> fwnode_find_reference()")
> Reported-by: Nuno Sá <nuno.sa@...log.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> 
> v2: adjusted the entire fwnode API (Sakari)
> 
> Nuno, can you test this with the ltc2983 series, including the
> IS_ERR_OR_NULL()
> fix to it?
> 

Sure... I will test that series together with this patch.
>  drivers/base/property.c | 45 +++++++++++++++++++++++++--------------
> --
>  include/linux/fwnode.h  | 10 ++++-----
>  2 files changed, 33 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/base/property.c b/drivers/base/property.c
> index c0e94cce9c29..1922818470b0 100644
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/acpi.h>
>  #include <linux/export.h>
> +#include <linux/fwnode.h>
>  #include <linux/kernel.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
> @@ -45,14 +46,16 @@ EXPORT_SYMBOL_GPL(device_property_present);
>  bool fwnode_property_present(const struct fwnode_handle *fwnode,
>                              const char *propname)
>  {
> -       bool ret;
> +       if (IS_ERR_OR_NULL(fwnode))
> +               return false;
>  
> -       ret = fwnode_call_bool_op(fwnode, property_present,
> propname);
> -       if (ret == false && !IS_ERR_OR_NULL(fwnode) &&
> -           !IS_ERR_OR_NULL(fwnode->secondary))
> -               ret = fwnode_call_bool_op(fwnode->secondary,
> property_present,
> -                                        propname);
> -       return ret;
> +       if (fwnode_call_bool_op(fwnode, property_present, propname))
> +               return true;
> +
> +       if (IS_ERR_OR_NULL(fwnode->secondary))
> +               return false;
> +
> +       return fwnode_call_bool_op(fwnode->secondary,
> property_present, propname);
>  }
>  EXPORT_SYMBOL_GPL(fwnode_property_present);
>  
> @@ -232,10 +235,12 @@ static int fwnode_property_read_int_array(const
> struct fwnode_handle *fwnode,
>  {
>         int ret;
>  
> +       if (IS_ERR_OR_NULL(fwnode))
> +               return -EINVAL;
> +
>         ret = fwnode_call_int_op(fwnode, property_read_int_array,
> propname,
>                                  elem_size, val, nval);
> -       if (ret == -EINVAL && !IS_ERR_OR_NULL(fwnode) &&
> -           !IS_ERR_OR_NULL(fwnode->secondary))
> +       if (ret == -EINVAL && !IS_ERR_OR_NULL(fwnode->secondary))
>                 ret = fwnode_call_int_op(
>                         fwnode->secondary, property_read_int_array,
> propname,
>                         elem_size, val, nval);
> @@ -371,10 +376,12 @@ int fwnode_property_read_string_array(const
> struct fwnode_handle *fwnode,
>  {
>         int ret;
>  
> +       if (IS_ERR_OR_NULL(fwnode))
> +               return -EINVAL;
> +
>         ret = fwnode_call_int_op(fwnode, property_read_string_array,
> propname,
>                                  val, nval);
> -       if (ret == -EINVAL && !IS_ERR_OR_NULL(fwnode) &&
> -           !IS_ERR_OR_NULL(fwnode->secondary))
> +       if (ret == -EINVAL && !IS_ERR_OR_NULL(fwnode->secondary))
>                 ret = fwnode_call_int_op(fwnode->secondary,
>                                          property_read_string_array,

Isn't !IS_ERR_OR_NULL(fwnode->secondary)) redundant? AFAIU,
fwnode_call_int_op() will already check the fwnode and only call the op
if the pointer is valid... 

- Nuno Sá