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authorJohannes Weiner <hannes@cmpxchg.org>2014-10-02 16:16:57 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-14 09:00:08 -0800
commitc65fabeffc5e5736465f89f1255c1953c9f60a9d (patch)
tree5f8934f1f9ee01563c7d6da1c51359dfd0df7415
parent3716dc8ceb39d47216059c0d494447d125d2b2f9 (diff)
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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@cmpxchg.org> Cc: Tejun Heo <tj@kernel.org> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: <stable@vger.kernel.org> [3.12+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--mm/memcontrol.c35
1 files changed, 31 insertions, 4 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9b35da28b587..b58d4fbe6c48 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -292,6 +292,9 @@ struct mem_cgroup {
/* vmpressure notifications */
struct vmpressure vmpressure;
+ /* css_online() has been completed */
+ int initialized;
+
/*
* the counter to account for mem+swap usage.
*/
@@ -1127,9 +1130,21 @@ 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)) {
+ /*
+ * Make sure the memcg is initialized:
+ * mem_cgroup_css_online() orders the the
+ * initialization against setting the flag.
+ */
+ if (smp_load_acquire(&memcg->initialized))
+ return memcg;
+ css_put(next_css);
+ }
prev_css = next_css;
goto skip_node;
@@ -6538,6 +6553,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(css));
+ int ret;
if (css->cgroup->id > MEM_CGROUP_ID_MAX)
return -ENOSPC;
@@ -6574,7 +6590,18 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
}
mutex_unlock(&memcg_create_mutex);
- return memcg_init_kmem(memcg, &mem_cgroup_subsys);
+ ret = memcg_init_kmem(memcg, &mem_cgroup_subsys);
+ if (ret)
+ return ret;
+
+ /*
+ * Make sure the memcg is initialized: mem_cgroup_iter()
+ * orders reading memcg->initialized against its callers
+ * reading the memcg members.
+ */
+ smp_store_release(&memcg->initialized, 1);
+
+ return 0;
}
/*