[Devel] [PATCH RHEL7 COMMIT] mm/memcg: initialize mem_cgroup_per_zone_info earlier.

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.5.1.vz7.84.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.5.1.vz7.84.2
------>
commit 1ab424b4ccb94d15bd35968f836579cf11993b51
Author: Andrey Ryabinin <aryabinin at virtuozzo.com>
Date:   Mon Mar 4 17:52:21 2019 +0300

    mm/memcg: initialize mem_cgroup_per_zone_info earlier.
    
    We are going to have the following piece of code.
    
    memcg = mem_cgroup_from_id(memcgid)
    lruvec = mem_cgroup_zone_lruvec(zone, memcg);
    
    This currently cannot work because mem_cgroup_per_zone_info
    allocated and initialized after memcgid become visible:
    
    mem_cgroup_alloc():
            idr_replace(&mem_cgroup_idr, memcg, memcg->id);
    
    Move per zone info initialization earlier, before idr_replace().
    Same thing was done in upstream commit 0b8f73e1("mm: memcontrol: clean
     up alloc, online, offline, free functions") but I don't want
    to do full backport, hence this patch.
    
    https://jira.sw.ru/browse/PSBM-91933
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/memcontrol.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 052b11501b8e..98cf7b56eaaa 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6260,6 +6260,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	size_t size;
 	int id;
 	int i, ret;
+	int node;
 
 	size = sizeof(struct mem_cgroup);
 	size += nr_node_ids * sizeof(struct mem_cgroup_per_node *);
@@ -6280,6 +6281,10 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	if (!memcg->stat)
 		goto out_free;
 
+	for_each_node(node)
+		if (alloc_mem_cgroup_per_zone_info(memcg, node))
+			goto out_free;
+
 	for (i = 0; i < MEM_CGROUP_STAT2_NSTATS; i++) {
 		ret = percpu_counter_init(&memcg->stat2.counters[i], 0, GFP_KERNEL);
 		if (ret)
@@ -6296,6 +6301,9 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 
 	free_percpu(memcg->stat);
 out_free:
+	for_each_node(node)
+		free_mem_cgroup_per_zone_info(memcg, node);
+
 	if (memcg->id > 0) {
 		idr_remove(&mem_cgroup_idr, memcg->id);
 		synchronize_rcu();
@@ -6385,16 +6393,11 @@ mem_cgroup_css_alloc(struct cgroup *cont)
 {
 	struct mem_cgroup *memcg;
 	long error = -ENOMEM;
-	int node;
 
 	memcg = mem_cgroup_alloc();
 	if (!memcg)
 		return ERR_PTR(error);
 
-	for_each_node(node)
-		if (alloc_mem_cgroup_per_zone_info(memcg, node))
-			goto free_out;
-
 	/* root ? */
 	if (cont->parent == NULL) {
 		root_mem_cgroup = memcg;