lkml.org 
[lkml]   [2016]   [Aug]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs
On Mon, Aug 15, 2016 at 04:04:39PM +0200, Michal Hocko wrote:
> On Mon 15-08-16 09:37:48, Johannes Weiner wrote:
> > On Mon, Aug 15, 2016 at 02:46:19PM +0200, Michal Hocko wrote:
> > > On Mon 15-08-16 08:34:07, Johannes Weiner wrote:
> > > > Hi Michal, thanks for doing this. There is only one issue I can see:
> > > >
> > > > On Fri, Aug 12, 2016 at 11:56:17AM +0200, Michal Hocko wrote:
> > > > > @@ -4171,17 +4211,27 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
> > > > > if (!memcg)
> > > > > return NULL;
> > > > >
> > > > > + memcg->id.id = idr_alloc(&mem_cgroup_idr, NULL,
> > > > > + 1, MEM_CGROUP_ID_MAX,
> > > > > + GFP_KERNEL);
> > > > > + if (memcg->id.id < 0)
> > > > > + goto out_free;
> > > > > +
> > > > > memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
> > > > > if (!memcg->stat)
> > > > > - goto out_free;
> > > > > + goto out_idr;
> > > > >
> > > > > if (memcg_wb_domain_init(memcg, GFP_KERNEL))
> > > > > goto out_free_stat;
> > > > >
> > > > > + idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
> > > >
> > > > This publishes the memcg object too early. Before 4.5, the memcg is
> > > > not fully initialized in mem_cgroup_alloc(). You have to move the
> > > > idr_replace() down to that function (and idr_remove() on free_out).
> > >
> > > You are right. I am just wondering whether it matters. Nobody should see
> > > the id so nobody will be looking it up, no?
> >
> > Page cache shadow entries refer to these IDs weakly. It's possible to
> > refault with a recently recycled memcg ID and crash. That's why we do
> > the whole alloc(NULL) -> replace(memcg) dance in the first place.
>
> Ahh, OK, you are right. So I have moved the idr_replace into
> mem_cgroup_css_alloc. Does the following incremental diff looks better?

Yep, looks good to me. Thanks!

\
 
 \ /
  Last update: 2016-09-17 09:56    [W:1.142 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site