Re: [PATCH 20/22] gpio: protect the pointer to gpio_chip in gpio_device with SRCU

[Dan Carpenter]

Hi Bartosz,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Bartosz-Golaszewski/gpio-protect-the-list-of-GPIO-devices-with-SRCU/20240130-205537
base:   https://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux.git gpio/for-next
patch link:    https://lore.kernel.org/r/20240130124828.14678-21-brgl%40bgdev.pl
patch subject: [PATCH 20/22] gpio: protect the pointer to gpio_chip in gpio_device with SRCU
config: i386-randconfig-141-20240131 (https://download.01.org/0day-ci/archive/20240201/202402010641.idtEaO24-lkp@xxxxxxxxx/config)
compiler: clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
| Closes: https://lore.kernel.org/r/202402010641.idtEaO24-lkp@xxxxxxxxx/

New smatch warnings:
drivers/gpio/gpiolib.c:4776 gpiolib_dbg_show() error: we previously assumed 'gc' could be null (see line 4773)


vim +/gc +4776 drivers/gpio/gpiolib.c

fdeb8e1547cb9d Linus Walleij       2016-02-10  4762  static void gpiolib_dbg_show(struct seq_file *s, struct gpio_device *gdev)
d2876d08d86f22 David Brownell      2008-02-04  4763  {
0338f6a6fb659f Bartosz Golaszewski 2023-12-21  4764  	bool active_low, is_irq, is_out;
0338f6a6fb659f Bartosz Golaszewski 2023-12-21  4765  	unsigned int gpio = gdev->base;
3de69ae1c407da Andy Shevchenko     2022-04-08  4766  	struct gpio_desc *desc;
2796d5332f8ac8 Bartosz Golaszewski 2024-01-30  4767  	struct gpio_chip *gc;
3de69ae1c407da Andy Shevchenko     2022-04-08  4768  	int value;
d2876d08d86f22 David Brownell      2008-02-04  4769  
2796d5332f8ac8 Bartosz Golaszewski 2024-01-30  4770  	guard(srcu)(&gdev->srcu);
2796d5332f8ac8 Bartosz Golaszewski 2024-01-30  4771  
2796d5332f8ac8 Bartosz Golaszewski 2024-01-30  4772  	gc = rcu_dereference(gdev->chip);
2796d5332f8ac8 Bartosz Golaszewski 2024-01-30 @4773  	if (!gc)
                                                            ^^^
The patch adds a NULL check

2796d5332f8ac8 Bartosz Golaszewski 2024-01-30  4774  		seq_puts(s, "Underlying GPIO chip is gone\n");
2796d5332f8ac8 Bartosz Golaszewski 2024-01-30  4775  
3de69ae1c407da Andy Shevchenko     2022-04-08 @4776  	for_each_gpio_desc(gc, desc) {
                                                                           ^^
But this dereference isn't checked...  Probably it should return after
the seq_puts().

bedc56b1695b27 Bartosz Golaszewski 2024-01-30  4777  		guard(srcu)(&desc->srcu);
3de69ae1c407da Andy Shevchenko     2022-04-08  4778  		if (test_bit(FLAG_REQUESTED, &desc->flags)) {
3de69ae1c407da Andy Shevchenko     2022-04-08  4779  			gpiod_get_direction(desc);
3de69ae1c407da Andy Shevchenko     2022-04-08  4780  			is_out = test_bit(FLAG_IS_OUT, &desc->flags);
234c52097ce416 Andy Shevchenko     2022-04-08  4781  			value = gpio_chip_get_value(gc, desc);
3de69ae1c407da Andy Shevchenko     2022-04-08  4782  			is_irq = test_bit(FLAG_USED_AS_IRQ, &desc->flags);
3de69ae1c407da Andy Shevchenko     2022-04-08  4783  			active_low = test_bit(FLAG_ACTIVE_LOW, &desc->flags);
3de69ae1c407da Andy Shevchenko     2022-04-08  4784  			seq_printf(s, " gpio-%-3d (%-20.20s|%-20.20s) %s %s %s%s\n",
32648f473c7f46 Bartosz Golaszewski 2024-01-30  4785  				   gpio, desc->name ?: "", gpiod_get_label(desc),
d2876d08d86f22 David Brownell      2008-02-04  4786  				   is_out ? "out" : "in ",
3de69ae1c407da Andy Shevchenko     2022-04-08  4787  				   value >= 0 ? (value ? "hi" : "lo") : "?  ",
90fd227029a25b Linus Walleij       2018-10-01  4788  				   is_irq ? "IRQ " : "",
90fd227029a25b Linus Walleij       2018-10-01  4789  				   active_low ? "ACTIVE LOW" : "");
3de69ae1c407da Andy Shevchenko     2022-04-08  4790  		} else if (desc->name) {
3de69ae1c407da Andy Shevchenko     2022-04-08  4791  			seq_printf(s, " gpio-%-3d (%-20.20s)\n", gpio, desc->name);
3de69ae1c407da Andy Shevchenko     2022-04-08  4792  		}
3de69ae1c407da Andy Shevchenko     2022-04-08  4793  
3de69ae1c407da Andy Shevchenko     2022-04-08  4794  		gpio++;
d2876d08d86f22 David Brownell      2008-02-04  4795  	}
d2876d08d86f22 David Brownell      2008-02-04  4796  }

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