On 10/08/2014, 04:00 PM, Johannes Weiner wrote: > This is for 3.12. smp_store_release() and smp_load_acquire() were > introduced only later, so this backport uses basic r/w barriers:
Thanks. Applied to 3.12. > --- > > From 3c2bc304874d63d2c35924a66b0985f623eac8fb Mon Sep 17 00:00:00 2001 > From: Johannes Weiner <[email protected]> > Date: Thu, 2 Oct 2014 16:16:57 -0700 > Subject: [patch] mm: memcontrol: do not iterate uninitialized memcgs > > commit 2f7dd7a4100ad4affcb141605bef178ab98ccb18 upstream. > > The cgroup iterators yield css objects that have not yet gone through > css_online(), but they are not complete memcgs at this point and so the > memcg iterators should not return them. Commit d8ad30559715 ("mm/memcg: > iteration skip memcgs not yet fully initialized") set out to implement > exactly this, but it uses CSS_ONLINE, a cgroup-internal flag that does > not meet the ordering requirements for memcg, and so the iterator may > skip over initialized groups, or return partially initialized memcgs. > > The cgroup core can not reasonably provide a clear answer on whether the > object around the css has been fully initialized, as that depends on > controller-specific locking and lifetime rules. Thus, introduce a > memcg-specific flag that is set after the memcg has been initialized in > css_online(), and read before mem_cgroup_iter() callers access the memcg > members. > > Signed-off-by: Johannes Weiner <[email protected]> > Cc: Tejun Heo <[email protected]> > Acked-by: Michal Hocko <[email protected]> > Cc: Hugh Dickins <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: <[email protected]> [3.12+] > Signed-off-by: Andrew Morton <[email protected]> > Signed-off-by: Linus Torvalds <[email protected]> > --- > mm/memcontrol.c | 33 ++++++++++++++++++++++++++++++--- > 1 file changed, 30 insertions(+), 3 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4e705ed74b81..ff648969e402 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -250,6 +250,9 @@ struct mem_cgroup { > /* vmpressure notifications */ > struct vmpressure vmpressure; > > + /* css_online() has been completed */ > + int initialized; > + > /* > * the counter to account for mem+swap usage. > */ > @@ -1089,9 +1092,23 @@ skip_node: > * skipping css reference should be safe. > */ > if (next_css) { > - if ((next_css == &root->css) || > - ((next_css->flags & CSS_ONLINE) && css_tryget(next_css))) > - return mem_cgroup_from_css(next_css); > + struct mem_cgroup *memcg = mem_cgroup_from_css(next_css); > + > + if (next_css == &root->css) > + return memcg; > + > + if (css_tryget(next_css)) { > + if (memcg->initialized) { > + /* > + * Make sure the memcg is initialized: > + * mem_cgroup_css_online() orders the the > + * initialization against setting the flag. > + */ > + smp_rmb(); > + return memcg; > + } > + css_put(next_css); > + } > > prev_css = next_css; > goto skip_node; > @@ -6331,6 +6348,16 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css) > > error = memcg_init_kmem(memcg, &mem_cgroup_subsys); > mutex_unlock(&memcg_create_mutex); > + > + if (!error) { > + /* > + * Make sure the memcg is initialized: mem_cgroup_iter() > + * orders reading memcg->initialized against its callers > + * reading the memcg members. > + */ > + smp_wmb(); > + memcg->initialized = 1; > + } > return error; > } > > -- js suse labs -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
