On Fri, May 29, 2020 at 01:40:32AM +0200, Frederic Weisbecker wrote:
> On Tue, May 26, 2020 at 06:11:02PM +0200, Peter Zijlstra wrote:
> > +/*
> > + * structure shares layout with single_call_data_t.
> > + */
> > struct irq_work {
> > - atomic_t flags;
> > struct llist_node llnode;
> > + atomic_t flags;
>
>
> We should probably have:
>
> struct csd_node {
> atomic_t flags;
> struct llist_node;
> }
>
> embed inside struct irq_work and struct __call_single_data. Relying on
> structure layout for things to work doesn't really clarify things :-)
Yes I know, but changing those structures is going to cause an aweful
lot of churn, and I didn't want to do that just now.. :-(
Also, there's more fun..
CSD_TYPE_SYNC/ASYNC:
struct {
struct llist_node node;
unsigned int flags;
smp_call_func_t func;
void *info;
};
CSD_TYPE_IRQ_WORK:
struct {
struct llist_node node;
atomic_t flags;
void (*func)(struct irq_work *);
};
CSD_TYPE_TTWU:
struct {
struct llist_node node;
unsigned int flags;
};
So while they all have a 'u32' sized @flags, irq_work wants it atomic.
Also, if we were to actually have the struct csd_node {}, you get a 4
byte hole when you embed it in task_struct.
This is all entirely fugly. No doubt about it.
But I failed to find a 'sane' way to express it and needed to get these
patches out because things were broken.
Maybe I can anonymous-union my way around it, dunno. I'll think about
it. I'm certainly not proud of this. But at least the BUILD_BUG_ON()s
should catch the more blatant breakage here.
