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Date: Fri, 21 Aug 2020 18:00:02 +0200 From: Bartosz Golaszewski <brgl@...ev.pl> To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Cc: Jonathan Cameron <jic23@...nel.org>, Hartmut Knaack <knaack.h@....de>, Lars-Peter Clausen <lars@...afoo.de>, Peter Meerwald-Stadler <pmeerw@...erw.net>, Michal Simek <michal.simek@...inx.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Guenter Roeck <linux@...ck-us.net>, linux-iio <linux-iio@...r.kernel.org>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Bartosz Golaszewski <bgolaszewski@...libre.com> Subject: Re: [PATCH v8 1/3] devres: provide devm_krealloc() On Fri, Aug 21, 2020 at 1:04 PM Andy Shevchenko <andriy.shevchenko@...ux.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@...ux.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
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