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 <hannes@xxxxxxxxxxx>
> 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 <hannes@xxxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> [3.12+]
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> ---
> 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
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