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    SubjectRe: [PATCH 20/22] gpio: protect the pointer to gpio_chip in gpio_device with SRCU
    On Wed, Jan 31, 2024 at 10:02:40AM +0100, Bartosz Golaszewski wrote:
    > On Wed, Jan 31, 2024 at 3:21 AM kernel test robot <lkp@intel.com> wrote:
    > >
    > > Hi Bartosz,
    > >
    > > kernel test robot noticed the following build warnings:
    > >
    > > [auto build test WARNING on brgl/gpio/for-next]
    > > [also build test WARNING on linus/master v6.8-rc2 next-20240130]
    > > [If your patch is applied to the wrong git tree, kindly drop us a note.
    > > And when submitting patch, we suggest to use '--base' as documented in
    > > 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: x86_64-randconfig-122-20240131 (https://download.01.org/0day-ci/archive/20240131/202401311050.YNdm98Hv-lkp@intel.com/config)
    > > compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
    > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240131/202401311050.YNdm98Hv-lkp@intel.com/reproduce)
    > >
    > > 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@intel.com>
    > > | Closes: https://lore.kernel.org/oe-kbuild-all/202401311050.YNdm98Hv-lkp@intel.com/
    > >
    > > sparse warnings: (new ones prefixed by >>)
    > > >> drivers/gpio/gpiolib.c:444:22: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:444:22: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:444:22: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c:1103:9: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:1103:9: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:1103:9: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c:1182:22: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:1182:22: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:1182:22: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c:2970:14: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:2970:14: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:2970:14: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c:3004:22: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:3004:22: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:3004:22: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c:3585:14: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:3585:14: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:3585:14: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c:4772:14: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:4772:14: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:4772:14: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c:4846:14: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.c:4846:14: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.c:4846:14: sparse: struct gpio_chip *
    > > drivers/gpio/gpiolib.c: note: in included file:
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > > >> drivers/gpio/gpiolib.h:202:1: sparse: sparse: incompatible types in comparison expression (different address spaces):
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip [noderef] __rcu *
    > > drivers/gpio/gpiolib.h:202:1: sparse: struct gpio_chip *
    > >
    > > vim +444 drivers/gpio/gpiolib.c
    > >
    > > 422
    > > 423 /*
    > > 424 * Convert a GPIO name to its descriptor
    > > 425 * Note that there is no guarantee that GPIO names are globally unique!
    > > 426 * Hence this function will return, if it exists, a reference to the first GPIO
    > > 427 * line found that matches the given name.
    > > 428 */
    > > 429 static struct gpio_desc *gpio_name_to_desc(const char * const name)
    > > 430 {
    > > 431 struct gpio_device *gdev;
    > > 432 struct gpio_desc *desc;
    > > 433 struct gpio_chip *gc;
    > > 434
    > > 435 if (!name)
    > > 436 return NULL;
    > > 437
    > > 438 guard(srcu)(&gpio_devices_srcu);
    > > 439
    > > 440 list_for_each_entry_srcu(gdev, &gpio_devices, list,
    > > 441 srcu_read_lock_held(&gpio_devices_srcu)) {
    > > 442 guard(srcu)(&gdev->srcu);
    > > 443
    > > > 444 gc = rcu_dereference(gdev->chip);
    > > 445 if (!gc)
    > > 446 continue;
    > > 447
    > > 448 for_each_gpio_desc(gc, desc) {
    > > 449 if (desc->name && !strcmp(desc->name, name))
    > > 450 return desc;
    > > 451 }
    > > 452 }
    > > 453
    > > 454 return NULL;
    > > 455 }
    > > 456
    > >
    > > --
    > > 0-DAY CI Kernel Test Service
    > > https://github.com/intel/lkp-tests/wiki
    >
    > Paul,
    >
    > Should I care about these warnings? They seem to be emitted for a lot
    > of RCU code already upstream. I'm not even sure how I'd go about
    > addressing them honestly.

    This is maintainer's choice.

    The fix would be to apply __rcu to the definition of ->chip. The benefit
    is that it finds bugs where rcu-protected pointers are used without RCU
    primitives and vice versa.

    Thanx, Paul

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