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SubjectRe: [RFC PATCH v1] devres: align devres.data strictly only for devm_kmalloc()
On Fri, Dec 20, 2019 at 03:06:55PM +0100, Peter Zijlstra wrote:
> On Fri, Dec 20, 2019 at 11:19:27AM +0100, Marc Gonzalez wrote:
> > Would anyone else have any suggestions, comments, insights, recommendations,
> > improvements, guidance, or wisdom? :-)
>
> Flip devres upside down!
>
> **WARNING, wear protective glasses when reading the below**
>
>
> struct devres {
> struct devres_node node;
> void *data;
> };
>
> /*
> * We place struct devres at the tail of the memory allocation
> * such that data retains the ARCH_KMALLOC_MINALIGN alignment.
> * struct devres itself is just 4 pointers and should therefore
> * only require trivial alignment.
> */
> static inline struct devres *data2devres(void *data)
> {
> return (struct devres *)(data + ksize(data) - sizeof(struct devres));
> }
>
> void *alloc_dr(...)
> {
> struct devres *dr;
> void *data;
>
> data = kmalloc(size + sizeof(struct devres), GFP_KERNEL);
> dr = data2devres(data);
> WARN_ON((unsigned long)dr & __alignof(*dr)-1);
> INIT_LIST_HEAD(&dr->node.entry);
> dr->node.release = release;
> dr->data = data;
>
> return dr;
> }
>
> void devres_free(void *data)
> {
> if (data) {
> struct devres *dr = data2devres(data);
> BUG_ON(!list_empty(dr->node.entry));
> kfree(data);
> }
> }
>
> static int release_nodes(...)
> {
> ...
> list_for_each_entry_safe_reverse(dr, ...) {
> ...
> kfree(dr->data);
> }
> }
>

Ok, that's my queue to walk away from the keyboard and start drinking, I
think the holiday season has now officially started.

ugh. crazy.

but brilliant :)

greg k-h

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