linux-kernel - Re: [PATCH v4] gpio: sim: fix an invalid _

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Date:   Tue, 19 Sep 2023 00:31:36 -0700
From:   brgl@...ev.pl
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        akpm@...ux-foundation.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: [PATCH v4] gpio: sim: fix an invalid __free() usage

On Mon, 18 Sep 2023 17:31:36 +0200, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> said:
> On Mon, Sep 18, 2023 at 04:55:33PM +0200, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>>
>> gpio_sim_make_line_names() returns NULL or ERR_PTR() so we must not use
>> __free(kfree) on the returned address. Split this function into two, one
>> that determines the size of the "gpio-line-names" array to allocate and
>> one that actually sets the names at correct offsets. The allocation and
>> assignment of the managed pointer happens in between.
>
> ...
>
>> +	unsigned int size = 0;
>>
>>  	list_for_each_entry(line, &bank->line_list, siblings) {
>> +		if (!line->name || (line->offset >= bank->num_lines))
>>  			continue;
>>
>> +		size = line->offset + 1;
>>  	}
>>
>> +	return size;
>
> So, now the function iterates over all lines and returns the size of the last
> match, correct?
>
> Why not
>
> 	list_for_each_entry_reversed() {
> 		if (line->name && ())
> 			break;
> 	}
>
> 	return size;
>
> ?

Because the line objects are not sorted by offset. They are added at the end
of the list in the order the user creates their corresponding configfs groups.

>
> ...
>
>> +static void
>> +gpio_sim_set_line_names(struct gpio_sim_bank *bank, char **line_names)
>> +{
>> +	struct gpio_sim_line *line;
>>
>>  	list_for_each_entry(line, &bank->line_list, siblings) {
>> -		if (line->offset >= bank->num_lines)
>> +		if (!line->name || (line->offset >= bank->num_lines))
>>  			continue;
>>
>> -		if (line->name && (line->offset <= max_offset))
>> -			line_names[line->offset] = line->name;
>> +		line_names[line->offset] = line->name;
>>  	}
>> -
>> -	return line_names;
>>  }
>
> Can be done in the similar (I see the difference) way for the consistency with
> above.
>
> ...
>
>> +	line_names_size = gpio_sim_get_line_names_size(bank);
>
>> +	if (line_names_size) {
>
> Of course this can be replace with...
>
>> +		line_names = kcalloc(line_names_size, sizeof(*line_names),
>> +				     GFP_KERNEL);
>
>> +		if (!line_names)
>
> ZERO_OR_NULL_PTR() check here, but I assume we discourage use of it.

Why? There are less than 40 instances of using it in the kernel. kmalloc()
returns NULL on failure.

Bart

>
>> +			return ERR_PTR(-ENOMEM);
>> +
>> +		gpio_sim_set_line_names(bank, line_names);
>>
>> -	if (line_names)
>>  		properties[prop_idx++] = PROPERTY_ENTRY_STRING_ARRAY_LEN(
>>  						"gpio-line-names",
>>  						line_names, line_names_size);
>> +	}
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
>