[PATCH v8 0/3] devres: provide and use devm_krealloc()

[PATCH v8 0/3] devres: provide and use devm_krealloc()

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Regular krealloc() obviously can't work with managed memory. This series
implements devm_krealloc() and adds two first users with hope that this
helper will be adopted by other drivers currently using non-managed
krealloc().

v1 -> v2:
- remove leftover call to hwmon_device_unregister() from pmbus_core.c
- add a patch extending devm_kmalloc() to handle zero size case
- use WARN_ON() instead of WARN_ONCE() in devm_krealloc() when passed
  a pointer to non-managed memory
- correctly handle the case when devm_krealloc() is passed a pointer to
  memory in .rodata (potentially returned by devm_kstrdup_const())
- correctly handle ZERO_SIZE_PTR passed as the ptr argument in devm_krealloc()

v2 -> v3:
- drop already applied patches
- collect Acks
- add an additional user in iio

v3 -> v4:
- add the kerneldoc for devm_krealloc()
- WARN() outside of spinlock
- rename local variable

v4 -> v5:
- tweak the kerneldoc

v5 -> v6:
- tweak the devres_lock handling in devm_krealloc()

v6 -> v7:
- rework devm_krealloc() to avoid calling krealloc() with spinlock taken

v7 -> v8:
- drop unnecessary explicit pointer casting in to_devres()
- check the return value of ksize() to make sure the pointer actually
  points to a dynamically allocated chunk
- add more comments to explain the locking strategy and resource handling

Bartosz Golaszewski (3):
  devres: provide devm_krealloc()
  hwmon: pmbus: use more devres helpers
  iio: adc: xilinx-xadc: use devm_krealloc()

 .../driver-api/driver-model/devres.rst        |   1 +
 drivers/base/devres.c                         | 114 ++++++++++++++++++
 drivers/hwmon/pmbus/pmbus_core.c              |  28 ++---
 drivers/iio/adc/xilinx-xadc-core.c            |  16 +--
 include/linux/device.h                        |   2 +
 5 files changed, 134 insertions(+), 27 deletions(-)

-- 
2.26.1

[PATCH v8 1/3] devres: provide devm_krealloc()

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Implement the managed variant of krealloc(). This function works with
all memory allocated by devm_kmalloc() (or devres functions using it
implicitly like devm_kmemdup(), devm_kstrdup() etc.).

Managed realloc'ed chunks can be manually released with devm_kfree().

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 .../driver-api/driver-model/devres.rst        |   1 +
 drivers/base/devres.c                         | 114 ++++++++++++++++++
 include/linux/device.h                        |   2 +
 3 files changed, 117 insertions(+)

diff --git a/Documentation/driver-api/driver-model/devres.rst b/Documentation/driver-api/driver-model/devres.rst
index eaaaafc21134..f318a5c0033c 100644
--- a/Documentation/driver-api/driver-model/devres.rst
+++ b/Documentation/driver-api/driver-model/devres.rst
@@ -354,6 +354,7 @@ MEM
   devm_kmalloc()
   devm_kmalloc_array()
   devm_kmemdup()
+  devm_krealloc()
   devm_kstrdup()
   devm_kvasprintf()
   devm_kzalloc()
diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index ed615d3b9cf1..55f3abb966ee 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -36,6 +36,16 @@ struct devres {
 	u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
 };
 
+static struct devres *to_devres(void *data)
+{
+	return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
+}
+
+static size_t devres_data_size(size_t total_size)
+{
+	return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
+}
+
 struct devres_group {
 	struct devres_node		node[2];
 	void				*id;
@@ -126,6 +136,14 @@ static void add_dr(struct device *dev, struct devres_node *node)
 	list_add_tail(&node->entry, &dev->devres_head);
 }
 
+static void replace_dr(struct device *dev,
+		       struct devres_node *old, struct devres_node *new)
+{
+	devres_log(dev, old, "REPLACE");
+	BUG_ON(!list_empty(&new->entry));
+	list_replace(&old->entry, &new->entry);
+}
+
 #ifdef CONFIG_DEBUG_DEVRES
 void * __devres_alloc_node(dr_release_t release, size_t size, gfp_t gfp, int nid,
 		      const char *name)
@@ -837,6 +855,102 @@ void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp)
 }
 EXPORT_SYMBOL_GPL(devm_kmalloc);
 
+/**
+ * devm_krealloc - Resource-managed krealloc()
+ * @dev: Device to re-allocate memory for
+ * @ptr: Pointer to the memory chunk to re-allocate
+ * @new_size: New allocation size
+ * @gfp: Allocation gfp flags
+ *
+ * Managed krealloc(). Resizes the memory chunk allocated with devm_kmalloc().
+ * Behaves similarly to regular krealloc(): if @ptr is NULL or ZERO_SIZE_PTR,
+ * it's the equivalent of devm_kmalloc(). If new_size is zero, it frees the
+ * previously allocated memory and returns ZERO_SIZE_PTR. This function doesn't
+ * change the order in which the release callback for the re-alloc'ed devres
+ * will be called (except when falling back to devm_kmalloc() or when freeing
+ * resources when new_size is zero). The contents of the memory are preserved
+ * up to the lesser of new and old sizes.
+ */
+void *devm_krealloc(struct device *dev, void *ptr, size_t new_size, gfp_t gfp)
+{
+	size_t total_new_size, total_old_size;
+	struct devres *old_dr, *new_dr;
+	unsigned long flags;
+
+	if (unlikely(!new_size)) {
+		devm_kfree(dev, ptr);
+		return ZERO_SIZE_PTR;
+	}
+
+	if (unlikely(ZERO_OR_NULL_PTR(ptr)))
+		return devm_kmalloc(dev, new_size, gfp);
+
+	if (WARN_ON(is_kernel_rodata((unsigned long)ptr)))
+		/*
+		 * We cannot reliably realloc a const string returned by
+		 * devm_kstrdup_const().
+		 */
+		return NULL;
+
+	if (!check_dr_size(new_size, &total_new_size))
+		return NULL;
+
+	total_old_size = ksize(to_devres(ptr));
+	if (total_old_size == 0) {
+		WARN(1, "Pointer doesn't point to dynamically allocated memory.");
+		return NULL;
+	}
+
+	/*
+	 * If new size is smaller or equal to the actual number of bytes
+	 * allocated previously - just return the same pointer.
+	 */
+	if (total_new_size <= total_old_size)
+		return ptr;
+
+	/*
+	 * Otherwise: allocate new, larger chunk. We need to allocate before
+	 * taking the lock as most probably the caller uses GFP_KERNEL.
+	 */
+	new_dr = alloc_dr(devm_kmalloc_release,
+			  total_new_size, gfp, dev_to_node(dev));
+	if (!new_dr)
+		return NULL;
+
+	/*
+	 * The spinlock protects the linked list against concurrent
+	 * modifications but not the resource itself.
+	 */
+	spin_lock_irqsave(&dev->devres_lock, flags);
+
+	old_dr = find_dr(dev, devm_kmalloc_release, devm_kmalloc_match, ptr);
+	if (!old_dr) {
+		spin_unlock_irqrestore(&dev->devres_lock, flags);
+		devres_free(new_dr);
+		WARN(1, "Memory chunk not managed or managed by a different device.");
+		return NULL;
+	}
+
+	replace_dr(dev, &old_dr->node, &new_dr->node);
+
+	spin_unlock_irqrestore(&dev->devres_lock, flags);
+
+	/*
+	 * We can copy the memory contents after releasing the lock as we're
+	 * no longer modyfing the list links.
+	 */
+	memcpy(new_dr->data, old_dr->data, devres_data_size(total_old_size));
+	/*
+	 * Same for releasing the old devres - it's now been removed from the
+	 * list. This is also the reason why we must not use devm_kfree() - the
+	 * links are no longer valid.
+	 */
+	kfree(old_dr);
+
+	return new_dr->data;
+}
+EXPORT_SYMBOL_GPL(devm_krealloc);
+
 /**
  * devm_kstrdup - Allocate resource managed space and
  *                copy an existing string into that.
diff --git a/include/linux/device.h b/include/linux/device.h
index ca18da4768e3..5da7d5f0a7ff 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -206,6 +206,8 @@ int devres_release_group(struct device *dev, void *id);
 
 /* managed devm_k.alloc/kfree for device drivers */
 void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) __malloc;
+void *devm_krealloc(struct device *dev, void *ptr, size_t size,
+		    gfp_t gfp) __must_check;
 __printf(3, 0) char *devm_kvasprintf(struct device *dev, gfp_t gfp,
 				     const char *fmt, va_list ap) __malloc;
 __printf(3, 4) char *devm_kasprintf(struct device *dev, gfp_t gfp,
-- 
2.26.1

[PATCH v8 2/3] hwmon: pmbus: use more devres helpers

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Shrink pmbus code by using devm_hwmon_device_register_with_groups()
and devm_krealloc() instead of their non-managed variants.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/pmbus/pmbus_core.c | 28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 44535add3a4a..91839979cf6c 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -1018,9 +1018,9 @@ static int pmbus_add_attribute(struct pmbus_data *data, struct attribute *attr)
 {
 	if (data->num_attributes >= data->max_attributes - 1) {
 		int new_max_attrs = data->max_attributes + PMBUS_ATTR_ALLOC_SIZE;
-		void *new_attrs = krealloc(data->group.attrs,
-					   new_max_attrs * sizeof(void *),
-					   GFP_KERNEL);
+		void *new_attrs = devm_krealloc(data->dev, data->group.attrs,
+						new_max_attrs * sizeof(void *),
+						GFP_KERNEL);
 		if (!new_attrs)
 			return -ENOMEM;
 		data->group.attrs = new_attrs;
@@ -2534,7 +2534,7 @@ int pmbus_do_probe(struct i2c_client *client, const struct i2c_device_id *id,
 
 	ret = pmbus_find_attributes(client, data);
 	if (ret)
-		goto out_kfree;
+		return ret;
 
 	/*
 	 * If there are no attributes, something is wrong.
@@ -2542,35 +2542,27 @@ int pmbus_do_probe(struct i2c_client *client, const struct i2c_device_id *id,
 	 */
 	if (!data->num_attributes) {
 		dev_err(dev, "No attributes found\n");
-		ret = -ENODEV;
-		goto out_kfree;
+		return -ENODEV;
 	}
 
 	data->groups[0] = &data->group;
 	memcpy(data->groups + 1, info->groups, sizeof(void *) * groups_num);
-	data->hwmon_dev = hwmon_device_register_with_groups(dev, client->name,
-							    data, data->groups);
+	data->hwmon_dev = devm_hwmon_device_register_with_groups(dev,
+					client->name, data, data->groups);
 	if (IS_ERR(data->hwmon_dev)) {
-		ret = PTR_ERR(data->hwmon_dev);
 		dev_err(dev, "Failed to register hwmon device\n");
-		goto out_kfree;
+		return PTR_ERR(data->hwmon_dev);
 	}
 
 	ret = pmbus_regulator_register(data);
 	if (ret)
-		goto out_unregister;
+		return ret;
 
 	ret = pmbus_init_debugfs(client, data);
 	if (ret)
 		dev_warn(dev, "Failed to register debugfs\n");
 
 	return 0;
-
-out_unregister:
-	hwmon_device_unregister(data->hwmon_dev);
-out_kfree:
-	kfree(data->group.attrs);
-	return ret;
 }
 EXPORT_SYMBOL_GPL(pmbus_do_probe);
 
@@ -2580,8 +2572,6 @@ int pmbus_do_remove(struct i2c_client *client)
 
 	debugfs_remove_recursive(data->debugfs);
 
-	hwmon_device_unregister(data->hwmon_dev);
-	kfree(data->group.attrs);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(pmbus_do_remove);
-- 
2.26.1

[PATCH v8 3/3] iio: adc: xilinx-xadc: use devm_krealloc()

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Use the managed variant of krealloc() and shrink the code a bit.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/iio/adc/xilinx-xadc-core.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
index d0b7ef296afb..f93c34fe5873 100644
--- a/drivers/iio/adc/xilinx-xadc-core.c
+++ b/drivers/iio/adc/xilinx-xadc-core.c
@@ -1092,6 +1092,7 @@ MODULE_DEVICE_TABLE(of, xadc_of_match_table);
 static int xadc_parse_dt(struct iio_dev *indio_dev, struct device_node *np,
 	unsigned int *conf)
 {
+	struct device *dev = indio_dev->dev.parent;
 	struct xadc *xadc = iio_priv(indio_dev);
 	struct iio_chan_spec *channels, *chan;
 	struct device_node *chan_node, *child;
@@ -1136,7 +1137,8 @@ static int xadc_parse_dt(struct iio_dev *indio_dev, struct device_node *np,
 		*conf |= XADC_CONF0_MUX | XADC_CONF0_CHAN(ext_mux_chan);
 	}
 
-	channels = kmemdup(xadc_channels, sizeof(xadc_channels), GFP_KERNEL);
+	channels = devm_kmemdup(dev, xadc_channels,
+				sizeof(xadc_channels), GFP_KERNEL);
 	if (!channels)
 		return -ENOMEM;
 
@@ -1172,8 +1174,9 @@ static int xadc_parse_dt(struct iio_dev *indio_dev, struct device_node *np,
 	of_node_put(chan_node);
 
 	indio_dev->num_channels = num_channels;
-	indio_dev->channels = krealloc(channels, sizeof(*channels) *
-					num_channels, GFP_KERNEL);
+	indio_dev->channels = devm_krealloc(dev, channels,
+					    sizeof(*channels) * num_channels,
+					    GFP_KERNEL);
 	/* If we can't resize the channels array, just use the original */
 	if (!indio_dev->channels)
 		indio_dev->channels = channels;
@@ -1225,14 +1228,14 @@ static int xadc_probe(struct platform_device *pdev)
 
 	ret = xadc_parse_dt(indio_dev, pdev->dev.of_node, &conf0);
 	if (ret)
-		goto err_device_free;
+		return ret;
 
 	if (xadc->ops->flags & XADC_FLAGS_BUFFERED) {
 		ret = iio_triggered_buffer_setup(indio_dev,
 			&iio_pollfunc_store_time, &xadc_trigger_handler,
 			&xadc_buffer_ops);
 		if (ret)
-			goto err_device_free;
+			return ret;
 
 		xadc->convst_trigger = xadc_alloc_trigger(indio_dev, "convst");
 		if (IS_ERR(xadc->convst_trigger)) {
@@ -1350,8 +1353,6 @@ static int xadc_probe(struct platform_device *pdev)
 err_triggered_buffer_cleanup:
 	if (xadc->ops->flags & XADC_FLAGS_BUFFERED)
 		iio_triggered_buffer_cleanup(indio_dev);
-err_device_free:
-	kfree(indio_dev->channels);
 
 	return ret;
 }
@@ -1371,7 +1372,6 @@ static int xadc_remove(struct platform_device *pdev)
 	cancel_delayed_work_sync(&xadc->zynq_unmask_work);
 	clk_disable_unprepare(xadc->clk);
 	kfree(xadc->data);
-	kfree(indio_dev->channels);
 
 	return 0;
 }
-- 
2.26.1

Re: [PATCH v8 1/3] devres: provide devm_krealloc()

[Andy Shevchenko]

On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> 
> Implement the managed variant of krealloc(). This function works with
> all memory allocated by devm_kmalloc() (or devres functions using it
> implicitly like devm_kmemdup(), devm_kstrdup() etc.).
> 
> Managed realloc'ed chunks can be manually released with devm_kfree().
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

...

> +static struct devres *to_devres(void *data)
> +{
> +	return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> +}
> +
> +static size_t devres_data_size(size_t total_size)
> +{
> +	return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> +}

I'm fine with above, but here is a side note, perhaps

	offsetof(struct devres,	data)

will be more practical (no duplication of alignment and hence slightly better
maintenance)? (Note, I didn't check if it provides the correct result)

Another side note: do we have existing users of these helpers?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v8 1/3] devres: provide devm_krealloc()

[Andy Shevchenko]

On Fri, Aug 21, 2020 at 11:15:55AM +0300, Andy Shevchenko wrote:
> On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:

...

> > +static struct devres *to_devres(void *data)
> > +{
> > +	return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > +}
> > +
> > +static size_t devres_data_size(size_t total_size)
> > +{
> > +	return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > +}
> 
> I'm fine with above, but here is a side note, perhaps
> 
> 	offsetof(struct devres,	data)
> 
> will be more practical (no duplication of alignment and hence slightly better
> maintenance)? (Note, I didn't check if it provides the correct result)

And if the result is correct wouldn't be first a simple container_of() after
all?

> Another side note: do we have existing users of these helpers?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v8 1/3] devres: provide devm_krealloc()

[Bartosz Golaszewski]

On Fri, Aug 21, 2020 at 10:35 AM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> >
> > Implement the managed variant of krealloc(). This function works with
> > all memory allocated by devm_kmalloc() (or devres functions using it
> > implicitly like devm_kmemdup(), devm_kstrdup() etc.).
> >
> > Managed realloc'ed chunks can be manually released with devm_kfree().
> >
> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>
> ...
>
> > +static struct devres *to_devres(void *data)
> > +{
> > +     return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > +}
> > +
> > +static size_t devres_data_size(size_t total_size)
> > +{
> > +     return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > +}
>
> I'm fine with above, but here is a side note, perhaps
>
>         offsetof(struct devres, data)
>
> will be more practical (no duplication of alignment and hence slightly better
> maintenance)? (Note, I didn't check if it provides the correct result)
>

Hi Andy,

The data pointer in struct devres is defined as:

    u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];

And this value (assigned the value of ARCH_DMA_MINALIGN) varies from
one arch to another. I wasn't really sure if offsetof() would work for
every case so I went with something very explicit.

> Another side note: do we have existing users of these helpers?
>

Which ones? Because I assume you're not referring to the ones I'm
adding in this patch. :)

Bart

Re: [PATCH v8 1/3] devres: provide devm_krealloc()

[Andy Shevchenko]

On Fri, Aug 21, 2020 at 10:59:19AM +0200, Bartosz Golaszewski wrote:
> On Fri, Aug 21, 2020 at 10:35 AM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

...

> > > +static struct devres *to_devres(void *data)
> > > +{
> > > +     return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > > +}
> > > +
> > > +static size_t devres_data_size(size_t total_size)
> > > +{
> > > +     return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > > +}
> >
> > I'm fine with above, but here is a side note, perhaps
> >
> >         offsetof(struct devres, data)
> >
> > will be more practical (no duplication of alignment and hence slightly better
> > maintenance)? (Note, I didn't check if it provides the correct result)
> >
> 
> Hi Andy,
> 
> The data pointer in struct devres is defined as:
> 
>     u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
> 
> And this value (assigned the value of ARCH_DMA_MINALIGN) varies from
> one arch to another. I wasn't really sure if offsetof() would work for
> every case so I went with something very explicit.

I have checked with a small program simulating to_devres() with your variant,
offsetof() and container_of().

The result is this: if MINALIGN < sizeof(long) and since struct is unpacked the
offsetof(), and thus container_of(), gives correct result, while ALIGN()
approach mistakenly moves pointer too back.

Test results
~~~~~~~~~~~~
sizeof(devres), ALIGN(data), resulting 3 pointers against NULL followed by
actual pointer of allocated struct and 3 pointers against it.

% for i in 1 2 4; do gcc -O2 -Wall -DSZ=$i -o test test.c && ./test | head -n1; done
szof: 24 a: 24 0xffffffffffffffe8 0xffffffffffffffef 0xffffffffffffffef, 0x55a3aa91e2a0: 0x55a3aa91e299 0x55a3aa91e2a0 0x55a3aa91e2a0
szof: 24 a: 24 0xffffffffffffffe8 0xffffffffffffffee 0xffffffffffffffee, 0x563d7b88b2a0: 0x563d7b88b29a 0x563d7b88b2a0 0x563d7b88b2a0
szof: 24 a: 24 0xffffffffffffffe8 0xffffffffffffffec 0xffffffffffffffec, 0x557d08cf82a0: 0x557d08cf829c 0x557d08cf82a0 0x557d08cf82a0

% for i in 1 2 4; do gcc -m32 -O2 -Wall -DSZ=$i -o test test.c && ./test | head -n1; done
szof: 12 a: 12 0xfffffff4 0xfffffff7 0xfffffff7, 0x584301a0: 0x5843019d 0x584301a0 0x584301a0
szof: 12 a: 12 0xfffffff4 0xfffffff6 0xfffffff6, 0x57bd61a0: 0x57bd619e 0x57bd61a0 0x57bd61a0
szof: 12 a: 12 0xfffffff4 0xfffffff4 0xfffffff4, 0x56b491a0: 0x56b491a0 0x56b491a0 0x56b491a0

I think you need to change this to use container_of() and offsetof().

> > Another side note: do we have existing users of these helpers?
> 
> Which ones? Because I assume you're not referring to the ones I'm
> adding in this patch. :)

Opposite, the ones you are introduced here. Meaning that we might convert
existing user(s) in the separate change(s) later on.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v8 1/3] devres: provide devm_krealloc()

[Andy Shevchenko]

On Fri, Aug 21, 2020 at 01:51:19PM +0300, Andy Shevchenko wrote:
> On Fri, Aug 21, 2020 at 10:59:19AM +0200, Bartosz Golaszewski wrote:
> > On Fri, Aug 21, 2020 at 10:35 AM Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> wrote:
> > > On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:

...

> > > > +static struct devres *to_devres(void *data)
> > > > +{
> > > > +     return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > > > +}
> > > > +
> > > > +static size_t devres_data_size(size_t total_size)
> > > > +{
> > > > +     return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > > > +}

> > The data pointer in struct devres is defined as:
> > 
> >     u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
> > 
> > And this value (assigned the value of ARCH_DMA_MINALIGN) varies from
> > one arch to another. I wasn't really sure if offsetof() would work for
> > every case so I went with something very explicit.
> 
> I have checked with a small program simulating to_devres() with your variant,
> offsetof() and container_of().
> 
> The result is this: if MINALIGN < sizeof(long) and since struct is unpacked the
> offsetof(), and thus container_of(), gives correct result, while ALIGN()
> approach mistakenly moves pointer too back.

...

> I think you need to change this to use container_of() and offsetof().

To be clear, there is probably no real problem, except unlikely possible
MINALIGN=4 on 64-bit arch, but for sake of the correctness.


-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v8 1/3] devres: provide devm_krealloc()

[Bartosz Golaszewski]

On Fri, Aug 21, 2020 at 1:04 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Fri, Aug 21, 2020 at 01:51:19PM +0300, Andy Shevchenko wrote:
> > On Fri, Aug 21, 2020 at 10:59:19AM +0200, Bartosz Golaszewski wrote:
> > > On Fri, Aug 21, 2020 at 10:35 AM Andy Shevchenko
> > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:
>
> ...
>
> > > > > +static struct devres *to_devres(void *data)
> > > > > +{
> > > > > +     return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > > > > +}
> > > > > +
> > > > > +static size_t devres_data_size(size_t total_size)
> > > > > +{
> > > > > +     return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > > > > +}
>
> > > The data pointer in struct devres is defined as:
> > >
> > >     u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
> > >
> > > And this value (assigned the value of ARCH_DMA_MINALIGN) varies from
> > > one arch to another. I wasn't really sure if offsetof() would work for
> > > every case so I went with something very explicit.
> >
> > I have checked with a small program simulating to_devres() with your variant,
> > offsetof() and container_of().
> >
> > The result is this: if MINALIGN < sizeof(long) and since struct is unpacked the
> > offsetof(), and thus container_of(), gives correct result, while ALIGN()
> > approach mistakenly moves pointer too back.
>
> ...
>
> > I think you need to change this to use container_of() and offsetof().
>
> To be clear, there is probably no real problem, except unlikely possible
> MINALIGN=4 on 64-bit arch, but for sake of the correctness.
>

Thanks for taking the time to check it. I'll switch to container_of()
for (hopefully) the last iteration.

Bart