From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
We're working towards removing the "multi-function" GPIO spinlock that's
implemented terribly wrong. We tried using an RW-semaphore to protect
the list of GPIO devices but it turned out that we still have old code
using legacy GPIO calls that need to translate the global GPIO number to
the address of the associated descriptor and - to that end - traverse
the list while holding the lock. If we change the spinlock to a sleeping
lock then we'll end up with "scheduling while atomic" bugs.
Let's allow lockless traversal of the list using SRCU and only use the
mutex when modyfing the list.
While at it: let's protect the period between when we start the lookup
and when we finally request the descriptor (increasing the reference
count of the GPIO device) with the SRCU read lock.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
drivers/gpio/gpiolib.c | 203 +++++++++++++++++++++--------------------
1 file changed, 104 insertions(+), 99 deletions(-)
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index d50a786f8176..69979de76485 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2,6 +2,7 @@
#include <linux/acpi.h>
#include <linux/bitmap.h>
+#include <linux/cleanup.h>
#include <linux/compat.h>
#include <linux/debugfs.h>
#include <linux/device.h>
@@ -14,12 +15,14 @@
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/list.h>
+#include <linux/lockdep.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/pinctrl/consumer.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
+#include <linux/srcu.h>
#include <linux/string.h>
#include <linux/gpio.h>
@@ -81,7 +84,12 @@ DEFINE_SPINLOCK(gpio_lock);
static DEFINE_MUTEX(gpio_lookup_lock);
static LIST_HEAD(gpio_lookup_list);
+
LIST_HEAD(gpio_devices);
+/* Protects the GPIO device list against concurrent modifications. */
+static DEFINE_MUTEX(gpio_devices_lock);
+/* Ensures coherence during read-only accesses to the list of GPIO devices. */
+DEFINE_STATIC_SRCU(gpio_devices_srcu);
static DEFINE_MUTEX(gpio_machine_hogs_mutex);
static LIST_HEAD(gpio_machine_hogs);
@@ -113,20 +121,16 @@ static inline void desc_set_label(struct gpio_desc *d, const char *label)
struct gpio_desc *gpio_to_desc(unsigned gpio)
{
struct gpio_device *gdev;
- unsigned long flags;
- spin_lock_irqsave(&gpio_lock, flags);
-
- list_for_each_entry(gdev, &gpio_devices, list) {
- if (gdev->base <= gpio &&
- gdev->base + gdev->ngpio > gpio) {
- spin_unlock_irqrestore(&gpio_lock, flags);
- return &gdev->descs[gpio - gdev->base];
+ scoped_guard(srcu, &gpio_devices_srcu) {
+ list_for_each_entry_srcu(gdev, &gpio_devices, list,
+ srcu_read_lock_held(&gpio_devices_srcu)) {
+ if (gdev->base <= gpio &&
+ gdev->base + gdev->ngpio > gpio)
+ return &gdev->descs[gpio - gdev->base];
}
}
- spin_unlock_irqrestore(&gpio_lock, flags);
-
if (!gpio_is_valid(gpio))
pr_warn("invalid GPIO %d\n", gpio);
@@ -282,7 +286,8 @@ static int gpiochip_find_base_unlocked(int ngpio)
struct gpio_device *gdev;
int base = GPIO_DYNAMIC_BASE;
- list_for_each_entry(gdev, &gpio_devices, list) {
+ list_for_each_entry_srcu(gdev, &gpio_devices, list,
+ lockdep_is_held(&gpio_devices_lock)) {
/* found a free space? */
if (gdev->base >= base + ngpio)
break;
@@ -354,23 +359,25 @@ static int gpiodev_add_to_list_unlocked(struct gpio_device *gdev)
{
struct gpio_device *prev, *next;
+ lockdep_assert_held(&gpio_devices_lock);
+
if (list_empty(&gpio_devices)) {
/* initial entry in list */
- list_add_tail(&gdev->list, &gpio_devices);
+ list_add_tail_rcu(&gdev->list, &gpio_devices);
return 0;
}
next = list_first_entry(&gpio_devices, struct gpio_device, list);
if (gdev->base + gdev->ngpio <= next->base) {
/* add before first entry */
- list_add(&gdev->list, &gpio_devices);
+ list_add_rcu(&gdev->list, &gpio_devices);
return 0;
}
prev = list_last_entry(&gpio_devices, struct gpio_device, list);
if (prev->base + prev->ngpio <= gdev->base) {
/* add behind last entry */
- list_add_tail(&gdev->list, &gpio_devices);
+ list_add_tail_rcu(&gdev->list, &gpio_devices);
return 0;
}
@@ -382,11 +389,13 @@ static int gpiodev_add_to_list_unlocked(struct gpio_device *gdev)
/* add between prev and next */
if (prev->base + prev->ngpio <= gdev->base
&& gdev->base + gdev->ngpio <= next->base) {
- list_add(&gdev->list, &prev->list);
+ list_add_rcu(&gdev->list, &prev->list);
return 0;
}
}
+ synchronize_srcu(&gpio_devices_srcu);
+
return -EBUSY;
}
@@ -399,26 +408,21 @@ static int gpiodev_add_to_list_unlocked(struct gpio_device *gdev)
static struct gpio_desc *gpio_name_to_desc(const char * const name)
{
struct gpio_device *gdev;
- unsigned long flags;
+ struct gpio_desc *desc;
if (!name)
return NULL;
- spin_lock_irqsave(&gpio_lock, flags);
-
- list_for_each_entry(gdev, &gpio_devices, list) {
- struct gpio_desc *desc;
+ guard(srcu)(&gpio_devices_srcu);
+ list_for_each_entry_srcu(gdev, &gpio_devices, list,
+ srcu_read_lock_held(&gpio_devices_srcu)) {
for_each_gpio_desc(gdev->chip, desc) {
- if (desc->name && !strcmp(desc->name, name)) {
- spin_unlock_irqrestore(&gpio_lock, flags);
+ if (desc->name && !strcmp(desc->name, name))
return desc;
- }
}
}
- spin_unlock_irqrestore(&gpio_lock, flags);
-
return NULL;
}
@@ -813,7 +817,6 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
struct lock_class_key *request_key)
{
struct gpio_device *gdev;
- unsigned long flags;
unsigned int i;
int base = 0;
int ret = 0;
@@ -878,49 +881,47 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
gdev->ngpio = gc->ngpio;
- spin_lock_irqsave(&gpio_lock, flags);
-
- /*
- * TODO: this allocates a Linux GPIO number base in the global
- * GPIO numberspace for this chip. In the long run we want to
- * get *rid* of this numberspace and use only descriptors, but
- * it may be a pipe dream. It will not happen before we get rid
- * of the sysfs interface anyways.
- */
- base = gc->base;
- if (base < 0) {
- base = gpiochip_find_base_unlocked(gc->ngpio);
+ scoped_guard(mutex, &gpio_devices_lock) {
+ /*
+ * TODO: this allocates a Linux GPIO number base in the global
+ * GPIO numberspace for this chip. In the long run we want to
+ * get *rid* of this numberspace and use only descriptors, but
+ * it may be a pipe dream. It will not happen before we get rid
+ * of the sysfs interface anyways.
+ */
+ base = gc->base;
if (base < 0) {
- spin_unlock_irqrestore(&gpio_lock, flags);
- ret = base;
- base = 0;
+ base = gpiochip_find_base_unlocked(gc->ngpio);
+ if (base < 0) {
+ ret = base;
+ base = 0;
+ goto err_free_label;
+ }
+
+ /*
+ * TODO: it should not be necessary to reflect the
+ * assigned base outside of the GPIO subsystem. Go over
+ * drivers and see if anyone makes use of this, else
+ * drop this and assign a poison instead.
+ */
+ gc->base = base;
+ } else {
+ dev_warn(&gdev->dev,
+ "Static allocation of GPIO base is deprecated, use dynamic allocation.\n");
+ }
+
+ gdev->base = base;
+
+ ret = gpiodev_add_to_list_unlocked(gdev);
+ if (ret) {
+ chip_err(gc, "GPIO integer space overlap, cannot add chip\n");
goto err_free_label;
}
- /*
- * TODO: it should not be necessary to reflect the assigned
- * base outside of the GPIO subsystem. Go over drivers and
- * see if anyone makes use of this, else drop this and assign
- * a poison instead.
- */
- gc->base = base;
- } else {
- dev_warn(&gdev->dev,
- "Static allocation of GPIO base is deprecated, use dynamic allocation.\n");
- }
- gdev->base = base;
-
- ret = gpiodev_add_to_list_unlocked(gdev);
- if (ret) {
- spin_unlock_irqrestore(&gpio_lock, flags);
- chip_err(gc, "GPIO integer space overlap, cannot add chip\n");
- goto err_free_label;
}
for (i = 0; i < gc->ngpio; i++)
gdev->descs[i].gdev = gdev;
- spin_unlock_irqrestore(&gpio_lock, flags);
-
BLOCKING_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier);
init_rwsem(&gdev->sem);
@@ -1011,9 +1012,9 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
goto err_print_message;
}
err_remove_from_list:
- spin_lock_irqsave(&gpio_lock, flags);
- list_del(&gdev->list);
- spin_unlock_irqrestore(&gpio_lock, flags);
+ scoped_guard(mutex, &gpio_devices_lock)
+ list_del_rcu(&gdev->list);
+ synchronize_srcu(&gpio_devices_srcu);
err_free_label:
kfree_const(gdev->label);
err_free_descs:
@@ -1076,8 +1077,9 @@ void gpiochip_remove(struct gpio_chip *gc)
dev_crit(&gdev->dev,
"REMOVING GPIOCHIP WITH GPIOS STILL REQUESTED\n");
- scoped_guard(spinlock_irqsave, &gpio_lock)
- list_del(&gdev->list);
+ scoped_guard(mutex, &gpio_devices_lock)
+ list_del_rcu(&gdev->list);
+ synchronize_srcu(&gpio_devices_srcu);
/*
* The gpiochip side puts its use of the device to rest here:
@@ -1125,7 +1127,7 @@ struct gpio_device *gpio_device_find(void *data,
*/
might_sleep();
- guard(spinlock_irqsave)(&gpio_lock);
+ guard(srcu)(&gpio_devices_srcu);
list_for_each_entry(gdev, &gpio_devices, list) {
if (gdev->chip && match(gdev->chip, data))
@@ -4136,27 +4138,32 @@ static struct gpio_desc *gpiod_find_and_request(struct device *consumer,
struct gpio_desc *desc;
int ret;
- desc = gpiod_find_by_fwnode(fwnode, consumer, con_id, idx, &flags, &lookupflags);
- if (gpiod_not_found(desc) && platform_lookup_allowed) {
+ scoped_guard(srcu, &gpio_devices_srcu) {
+ desc = gpiod_find_by_fwnode(fwnode, consumer, con_id, idx,
+ &flags, &lookupflags);
+ if (gpiod_not_found(desc) && platform_lookup_allowed) {
+ /*
+ * Either we are not using DT or ACPI, or their lookup
+ * did not return a result. In that case, use platform
+ * lookup as a fallback.
+ */
+ dev_dbg(consumer,
+ "using lookup tables for GPIO lookup\n");
+ desc = gpiod_find(consumer, con_id, idx, &lookupflags);
+ }
+
+ if (IS_ERR(desc)) {
+ dev_dbg(consumer, "No GPIO consumer %s found\n",
+ con_id);
+ return desc;
+ }
+
/*
- * Either we are not using DT or ACPI, or their lookup did not
- * return a result. In that case, use platform lookup as a
- * fallback.
+ * If a connection label was passed use that, else attempt to use
+ * the device name as label
*/
- dev_dbg(consumer, "using lookup tables for GPIO lookup\n");
- desc = gpiod_find(consumer, con_id, idx, &lookupflags);
+ ret = gpiod_request(desc, label);
}
-
- if (IS_ERR(desc)) {
- dev_dbg(consumer, "No GPIO consumer %s found\n", con_id);
- return desc;
- }
-
- /*
- * If a connection label was passed use that, else attempt to use
- * the device name as label
- */
- ret = gpiod_request(desc, label);
if (ret) {
if (!(ret == -EBUSY && flags & GPIOD_FLAGS_BIT_NONEXCLUSIVE))
return ERR_PTR(ret);
@@ -4727,35 +4734,33 @@ static void gpiolib_dbg_show(struct seq_file *s, struct gpio_device *gdev)
static void *gpiolib_seq_start(struct seq_file *s, loff_t *pos)
{
- unsigned long flags;
struct gpio_device *gdev = NULL;
loff_t index = *pos;
s->private = "";
- spin_lock_irqsave(&gpio_lock, flags);
- list_for_each_entry(gdev, &gpio_devices, list)
- if (index-- == 0) {
- spin_unlock_irqrestore(&gpio_lock, flags);
+ guard(srcu)(&gpio_devices_srcu);
+
+ list_for_each_entry(gdev, &gpio_devices, list) {
+ if (index-- == 0)
return gdev;
- }
- spin_unlock_irqrestore(&gpio_lock, flags);
+ }
return NULL;
}
static void *gpiolib_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
- unsigned long flags;
struct gpio_device *gdev = v;
void *ret = NULL;
- spin_lock_irqsave(&gpio_lock, flags);
- if (list_is_last(&gdev->list, &gpio_devices))
- ret = NULL;
- else
- ret = list_first_entry(&gdev->list, struct gpio_device, list);
- spin_unlock_irqrestore(&gpio_lock, flags);
+ scoped_guard(srcu, &gpio_devices_srcu) {
+ if (list_is_last(&gdev->list, &gpio_devices))
+ ret = NULL;
+ else
+ ret = list_first_entry(&gdev->list, struct gpio_device,
+ list);
+ }
s->private = "\n";
++*pos;
--
2.40.1On Tue, Jan 30, 2024 at 1:48 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote: > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > We're working towards removing the "multi-function" GPIO spinlock that's > implemented terribly wrong. We tried using an RW-semaphore to protect > the list of GPIO devices but it turned out that we still have old code > using legacy GPIO calls that need to translate the global GPIO number to > the address of the associated descriptor and - to that end - traverse > the list while holding the lock. If we change the spinlock to a sleeping > lock then we'll end up with "scheduling while atomic" bugs. > > Let's allow lockless traversal of the list using SRCU and only use the > mutex when modyfing the list. > > While at it: let's protect the period between when we start the lookup > and when we finally request the descriptor (increasing the reference > count of the GPIO device) with the SRCU read lock. > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> This looks to be doing the right thing to my RCU-untrained eye, so: Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Yours, Linus Walleij
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-20240131]
[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/20240130124828.14678-2-brgl%40bgdev.pl
patch subject: [PATCH 01/22] gpio: protect the list of GPIO devices with SRCU
config: i386-randconfig-141-20240131 (https://download.01.org/0day-ci/archive/20240131/202401311746.be3dlVTg-lkp@intel.com/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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202401311746.be3dlVTg-lkp@intel.com/
New smatch warnings:
drivers/gpio/gpiolib.c:4167 gpiod_find_and_request() error: uninitialized symbol 'ret'.
drivers/gpio/gpiolib.c:4181 gpiod_find_and_request() error: uninitialized symbol 'desc'.
Old smatch warnings:
drivers/gpio/gpiolib.c:4184 gpiod_find_and_request() error: uninitialized symbol 'desc'.
vim +/ret +4167 drivers/gpio/gpiolib.c
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4128
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4129 static struct gpio_desc *gpiod_find_and_request(struct device *consumer,
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4130 struct fwnode_handle *fwnode,
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4131 const char *con_id,
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4132 unsigned int idx,
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4133 enum gpiod_flags flags,
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4134 const char *label,
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4135 bool platform_lookup_allowed)
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4136 {
ba2dc1cb5491712 Hans de Goede 2022-12-29 4137 unsigned long lookupflags = GPIO_LOOKUP_FLAGS_DEFAULT;
c122f461ccac0e7 Andy Shevchenko 2023-03-09 4138 struct gpio_desc *desc;
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4139 int ret;
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4140
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4141 scoped_guard(srcu, &gpio_devices_srcu) {
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4142 desc = gpiod_find_by_fwnode(fwnode, consumer, con_id, idx,
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4143 &flags, &lookupflags);
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4144 if (gpiod_not_found(desc) && platform_lookup_allowed) {
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4145 /*
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4146 * Either we are not using DT or ACPI, or their lookup
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4147 * did not return a result. In that case, use platform
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4148 * lookup as a fallback.
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4149 */
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4150 dev_dbg(consumer,
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4151 "using lookup tables for GPIO lookup\n");
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4152 desc = gpiod_find(consumer, con_id, idx, &lookupflags);
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4153 }
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4154
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4155 if (IS_ERR(desc)) {
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4156 dev_dbg(consumer, "No GPIO consumer %s found\n",
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4157 con_id);
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4158 return desc;
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4159 }
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4160
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4161 /*
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4162 * If a connection label was passed use that, else attempt to use
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4163 * the device name as label
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4164 */
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4165 ret = gpiod_request(desc, label);
1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4166 }
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 @4167 if (ret) {
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4168 if (!(ret == -EBUSY && flags & GPIOD_FLAGS_BIT_NONEXCLUSIVE))
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4169 return ERR_PTR(ret);
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4170
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4171 /*
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4172 * This happens when there are several consumers for
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4173 * the same GPIO line: we just return here without
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4174 * further initialization. It is a bit of a hack.
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4175 * This is necessary to support fixed regulators.
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4176 *
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4177 * FIXME: Make this more sane and safe.
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4178 */
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4179 dev_info(consumer,
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4180 "nonexclusive access to GPIO for %s\n", con_id);
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 @4181 return desc;
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4182 }
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4183
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4184 ret = gpiod_configure_flags(desc, con_id, lookupflags, flags);
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4185 if (ret < 0) {
8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4186 dev_dbg(consumer, "setup of GPIO %s failed\n", con_id);
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4187 gpiod_put(desc);
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4188 return ERR_PTR(ret);
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4189 }
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4190
9ce4ed5b4db1363 Bartosz Golaszewski 2023-08-21 4191 gpiod_line_state_notify(desc, GPIOLINE_CHANGED_REQUESTED);
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4192
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4193 return desc;
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4194 }
0eadd36d9123745 Dmitry Torokhov 2022-09-03 4195
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On Wed, Jan 31, 2024 at 10:37 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-20240131]
> [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/20240130124828.14678-2-brgl%40bgdev.pl
> patch subject: [PATCH 01/22] gpio: protect the list of GPIO devices with SRCU
> config: i386-randconfig-141-20240131 (https://download.01.org/0day-ci/archive/20240131/202401311746.be3dlVTg-lkp@intel.com/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@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202401311746.be3dlVTg-lkp@intel.com/
>
> New smatch warnings:
> drivers/gpio/gpiolib.c:4167 gpiod_find_and_request() error: uninitialized symbol 'ret'.
> drivers/gpio/gpiolib.c:4181 gpiod_find_and_request() error: uninitialized symbol 'desc'.
>
> Old smatch warnings:
> drivers/gpio/gpiolib.c:4184 gpiod_find_and_request() error: uninitialized symbol 'desc'.
>
> vim +/ret +4167 drivers/gpio/gpiolib.c
>
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4128
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4129 static struct gpio_desc *gpiod_find_and_request(struct device *consumer,
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4130 struct fwnode_handle *fwnode,
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4131 const char *con_id,
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4132 unsigned int idx,
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4133 enum gpiod_flags flags,
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4134 const char *label,
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4135 bool platform_lookup_allowed)
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4136 {
> ba2dc1cb5491712 Hans de Goede 2022-12-29 4137 unsigned long lookupflags = GPIO_LOOKUP_FLAGS_DEFAULT;
> c122f461ccac0e7 Andy Shevchenko 2023-03-09 4138 struct gpio_desc *desc;
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4139 int ret;
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4140
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4141 scoped_guard(srcu, &gpio_devices_srcu) {
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4142 desc = gpiod_find_by_fwnode(fwnode, consumer, con_id, idx,
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4143 &flags, &lookupflags);
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4144 if (gpiod_not_found(desc) && platform_lookup_allowed) {
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4145 /*
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4146 * Either we are not using DT or ACPI, or their lookup
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4147 * did not return a result. In that case, use platform
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4148 * lookup as a fallback.
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4149 */
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4150 dev_dbg(consumer,
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4151 "using lookup tables for GPIO lookup\n");
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4152 desc = gpiod_find(consumer, con_id, idx, &lookupflags);
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4153 }
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4154
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4155 if (IS_ERR(desc)) {
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4156 dev_dbg(consumer, "No GPIO consumer %s found\n",
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4157 con_id);
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4158 return desc;
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4159 }
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4160
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4161 /*
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4162 * If a connection label was passed use that, else attempt to use
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4163 * the device name as label
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4164 */
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4165 ret = gpiod_request(desc, label);
> 1fe5210a1bfba00 Bartosz Golaszewski 2024-01-30 4166 }
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 @4167 if (ret) {
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4168 if (!(ret == -EBUSY && flags & GPIOD_FLAGS_BIT_NONEXCLUSIVE))
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4169 return ERR_PTR(ret);
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4170
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4171 /*
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4172 * This happens when there are several consumers for
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4173 * the same GPIO line: we just return here without
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4174 * further initialization. It is a bit of a hack.
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4175 * This is necessary to support fixed regulators.
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4176 *
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4177 * FIXME: Make this more sane and safe.
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4178 */
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4179 dev_info(consumer,
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4180 "nonexclusive access to GPIO for %s\n", con_id);
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 @4181 return desc;
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4182 }
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4183
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4184 ret = gpiod_configure_flags(desc, con_id, lookupflags, flags);
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4185 if (ret < 0) {
> 8eb1f71e7acca4f Dmitry Torokhov 2022-11-11 4186 dev_dbg(consumer, "setup of GPIO %s failed\n", con_id);
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4187 gpiod_put(desc);
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4188 return ERR_PTR(ret);
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4189 }
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4190
> 9ce4ed5b4db1363 Bartosz Golaszewski 2023-08-21 4191 gpiod_line_state_notify(desc, GPIOLINE_CHANGED_REQUESTED);
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4192
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4193 return desc;
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4194 }
> 0eadd36d9123745 Dmitry Torokhov 2022-09-03 4195
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
This is a false-positive coming from the fact the scoped_guard() is
implemented as a for loop. I will initialize the variables anyway to
make smatch happy.
Bart
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