Re: [RFC PATCH 1/1] epoll: use rwlock in order to reduce ep_poll_callback() contention

[Roman Penyaev]

On 2018-12-05 00:59, Andrea Parri wrote:
> Hi Roman,
>
> On Tue, Dec 04, 2018 at 12:50:58PM +0100, Roman Penyaev wrote:
> > On 2018-12-03 18:34, Linus Torvalds wrote:
>
> > > This also ends up making the memory ordering of "xchg()" very very
> > > important. Yes, we've documented it as being an ordering op, but I'm
> > > not sure we've relied on it this directly before.
> >
> > Seems exit_mm() does exactly the same, the following chunk:
> >
> > 		up_read(&mm->mmap_sem);
> >
> > 		self.task = current;
> > 		self.next = xchg(&core_state->dumper.next, &self);
> >
> >
> > At least code pattern looks similar.
>
> Maybe add a comment on top of (your) xchg() to note/justify these 
> memory
> ordering requirements?  As Paul said: "if there are races, this would
> help force them to happen" (and simplify the review, this/future).

Hi Andrea,

Sure, this path is tricky, so will I cook something up.

--
Roman