Messages in this thread | | | Date | Tue, 23 Jun 2009 13:44:20 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RFC][PATCH] cgroup: fix permanent wait in rmdir |
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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().
> > > +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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