On Tue, Nov 19, 2019 at 07:57:04AM -0800, Matthew Wilcox wrote:
> On Tue, Nov 19, 2019 at 08:23:17PM +0800, Alex Shi wrote:
> > +static inline struct lruvec *lock_page_lruvec_irqsave(struct page *page,
> > + struct pglist_data *pgdat, unsigned long *flags)
> > +{
> > + struct lruvec *lruvec = mem_cgroup_page_lruvec(page, pgdat);
> > +
> > + spin_lock_irqsave(&lruvec->lru_lock, *flags);
> > +
> > + return lruvec;
> > +}
>
> This should be a macro, not a function. You basically can't do this;
> spin_lock_irqsave needs to write to a variable which can then be passed
> to spin_unlock_irqrestore(). What you're doing here will dereference the
> pointer in _this_ function, but won't propagate the modified value back to
> the caller. I suppose you could do something like this ...
This works because spin_lock_irqsave and local_irq_save() are
macros. It boils down to '*flags = arch_local_irq_save()' in this
function, and therefor does the right thing.
We exploit that in quite a few places:
$ git grep 'spin_lock_irqsave(.*\*flags' | wc -l
39
