devres: provide and use devm_krealloc()

From: Bartosz Golaszewski <[email protected]>

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 <[email protected]>

Reviewed-by Andy Shevchenko <[email protected]>

On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:

drivers/base/devres.c struct devres { · line 47

Quoted 9 lines

drivers/base/devres.c +9 -0

+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?

Quoted 10 lines · Bartosz Golaszewski

From: Bartosz Golaszewski <[email protected]>

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 <[email protected]>

Reviewed-by Andy Shevchenko <[email protected]>

...

drivers/base/devres.c struct devres { · line 47

Quoted 9 lines

drivers/base/devres.c +9 -0

+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?

Quoted 2 lines · Andy Shevchenko

Quoted 1 line · Bartosz Golaszewski

From: Bartosz Golaszewski <[email protected]>

Quoted 12 lines

drivers/base/devres.c struct devres { · line 47

Quoted 9 lines

drivers/base/devres.c +9 -0

+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

Quoted 5 lines

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.

Quoted 1 line

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. :)

Quoted 3 lines · Bartosz Golaszewski

Quoted 1 line · Andy Shevchenko

On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:

Quoted 12 lines

Quoted 9 lines

drivers/base/devres.c struct devres { · line 47

Quoted 9 lines

drivers/base/devres.c +9 -0

+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:

Quoted 5 lines

    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().

Quoted 4 lines · Andy Shevchenko

Quoted 3 lines · Bartosz Golaszewski

Quoted 1 line · Andy Shevchenko

On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:

...

Quoted 18 lines

Quoted 12 lines

Quoted 9 lines

drivers/base/devres.c struct devres { · line 47

Quoted 9 lines

drivers/base/devres.c +9 -0

+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:

Quoted 5 lines

    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.

Quoted 6 lines

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.

...

Quoted 1 line

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.