On Thu, Dec 21, 2017 at 09:31:23AM -0800, Rao Shoaib wrote:
>
>
> On 12/21/2017 04:36 AM, Matthew Wilcox wrote:
> >On Thu, Dec 21, 2017 at 12:19:47AM -0800, rao.shoaib@xxxxxxxxxx wrote:
> >>This patch moves kfree_call_rcu() and related macros out of rcu code. A new
> >>function __call_rcu_lazy() is created for calling __call_rcu() with the lazy
> >>flag.
> >Something you probably didn't know ... there are two RCU implementations
> >in the kernel; Tree and Tiny. It looks like you've only added
> >__call_rcu_lazy() to Tree and you'll also need to add it to Tiny.
> I left it out on purpose because the call in tiny is a little different
>
> rcutiny.h:
>
> static inline void kfree_call_rcu(struct rcu_head *head,
> void (*func)(struct rcu_head *rcu))
> {
> call_rcu(head, func);
> }
>
> tree.c:
>
> void kfree_call_rcu(struct rcu_head *head,
> void (*func)(struct rcu_head *rcu))
> {
> __call_rcu(head, func, rcu_state_p, -1, 1);
> }
> EXPORT_SYMBOL_GPL(kfree_call_rcu);
>
> If we want the code to be exactly same I can create a lazy version
> for tiny as well. However, I don not know where to move
> kfree_call_rcu() from it's current home in rcutiny.h though. Any
> thoughts ?
I might be missing something subtle here, but in case I am not, my
suggestion is to simply rename rcutiny.h's kfree_call_rcu() and otherwise
leave it as is. If you want to update the type of the second argument,
which got missed back in the day, there is always this:
static inline void call_rcu_lazy(struct rcu_head *head, rcu_callback_t func)
{
call_rcu(head, func);
}
The reason that Tiny RCU doesn't handle laziness specially is because
Tree RCU's handling of laziness is a big no-op on the single CPU systems
on which Tiny RCU runs. So Tiny RCU need do nothing special to support
laziness.
Thanx, Paul
> >>Also moving macros generated following checkpatch noise. I do not know
> >>how to silence checkpatch as there is nothing wrong.
> >>
> >>CHECK: Macro argument reuse 'offset' - possible side-effects?
> >>#91: FILE: include/linux/slab.h:348:
> >>+#define __kfree_rcu(head, offset) \
> >>+ do { \
> >>+ BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
> >>+ kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
> >>+ } while (0)
> >What checkpatch is warning you about here is that somebody might call
> >
> >__kfree_rcu(p, a++);
> >
> >and this would expand into
> >
> > do { \
> > BUILD_BUG_ON(!__is_kfree_rcu_offset(a++)); \
> > kfree_call_rcu(p, (rcu_callback_t)(unsigned long)(a++)); \
> > } while (0)
> >
> >which would increment 'a' twice, and cause pain and suffering.
> >
> >That's pretty unlikely usage of __kfree_rcu(), but I suppose it's not
> >impossible. We have various hacks to get around this kind of thing;
> >for example I might do this as::
> >
> >#define __kfree_rcu(head, offset) \
> > do { \
> > unsigned long __o = offset;
> > BUILD_BUG_ON(!__is_kfree_rcu_offset(__o)); \
> > kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(__o)); \
> > } while (0)
> >
> >Now offset is only evaluated once per invocation of the macro. The other
> >two warnings are the same problem.
> >
> Thanks. I was not sure if I was required to fix the noise or based
> on inspection the noise could be ignored. I will make the change and
> resubmit.
>
> Shoaib
>
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