Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm()

[Tejun Heo]

On Fri, Nov 15, 2019 at 06:47:21PM +0100, Michal Hocko wrote:
> s@online@offline@
> 
> And reading after myself it turned out to sound differently than I
> meant. What I wanted to say really is, what is the difference that
> css_tryget_online really guarantee when the css might go offline right
> after the call suceeds so more specifically what is the difference
> between
> 	if (css_tryget()) {
> 		if (online)
> 			DO_SOMETHING
> 	}
> and
> 	if (css_tryget_online()) {
> 		DO_SOMETHING
> 	}
> 
> both of them are racy and do not provide any guarantee wrt. online
> state.

It's about not giving new reference when the object is known to be
delted to the user.  Can you please think more about how file
deletions work?

Thanks.

-- 
tejun