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SubjectRe: [RFC][PATCH] cgroup: fix permanent wait in rmdir
On Tue, 23 Jun 2009 13:44:20 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Tue, 23 Jun 2009 13:13:33 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
>
> > On Tue, 23 Jun 2009 09:22:23 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > > On Mon, 22 Jun 2009 18:37:07 +0900
> > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > >
> > > > previous discussion was this => http://marc.info/?t=124478543600001&r=1&w=2
> > > >
> > > > I think this is a minimum fix (in code size and behavior) and because
> > > > we can take a BIG LOCK, this kind of check is necessary, anyway.
> > > > Any comments are welcome.
> > >
> > > I'll split this into 2 patches...and I found I should check page-migration, too.
> > I'll wait a new version, but can you explain in advance this page-migration case ?
> >
>
> Not far from swap-in case.
>
> Assume cgroup "A" which includes file caches. A task in other group mmap file caches
> and do page migration and rmdir against "A" is called at the same time.
>
> In mem_cgroup_prepare_migration(), following check is used.
>
> ==
> lock_page_cgroup(pc);
> if (PageCgroupUsed(pc)) {
> mem = pc->mem_cgroup;
> css_get(&mem->css);
> }
> unlock_page_cgroup(pc);
> <======================================(*)
> if (mem) {
> <==============================(**)
> try_charge();
> ...
> }
> ==
>
> At (*), we grab css refcnt which can be under pre_destroy() and
> At (**), pre_destroy may returns 0 but charge may be done after the end of pre_destroy().
>
Ah I see, you're right.

Thank you for your clarification.

Daisuke Nishimura.

>
> > > > +static int mem_cgroup_retry_rmdir(struct cgroup_subsys *ss,
> > > > + struct cgroup *cont)
> > > > +{
> > > > + struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
> > > > +
> > > > + if (res_counter_read_u64(&memcg->res, RES_USAGE))
> > It should be &mem->res.
> >
> yes.
> too many typos in my patches in these days..
>
> Thanks,
> -Kame
>


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