mm: memcontrol: do not iterate uninitialized memcgs (2f7dd7a4) · Commits · 戴 / test

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 ("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>

mm/memcontrol.c

+31 −5

Original line number	Diff line number	Diff line
		@@ -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.
		*/
		@@ -1099,10 +1102,21 @@ skip_node:
		* skipping css reference should be safe.
		*/
		if (next_css) {
		if ((next_css == &root->css) \|\|
		((next_css->flags & CSS_ONLINE) &&
		css_tryget_online(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_online(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;
		@@ -5549,6 +5563,7 @@ 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);
		int ret;

		if (css->id > MEM_CGROUP_ID_MAX)
		return -ENOSPC;
		@@ -5585,7 +5600,18 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
		}
		mutex_unlock(&memcg_create_mutex);

		return memcg_init_kmem(memcg, &memory_cgrp_subsys);
		ret = memcg_init_kmem(memcg, &memory_cgrp_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;
		}

		/*

Admin message