[Devel] [PATCH RHEL7 COMMIT] memcg: add lock for protecting memcg->oom_notify list

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-229.7.2.vz7.8.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-229.7.2.vz7.8.6
------>
commit f86c874c39188e9af50163092e161878a1067977
Author: Vladimir Davydov <vdavydov at parallels.com>
Date:   Thu Oct 15 17:52:59 2015 +0400

    memcg: add lock for protecting memcg->oom_notify list
    
    Patchset description: oom enhancements - part 2
    
     - Patches 1-2 prepare memcg for upcoming changes in oom design.
     - Patch 3 reworks oom locking design so that the executioner waits for
       victim to exit. This is necessary to increase oom kill rate, which is
       essential for berserker mode.
     - Patch 4 drops unused OOM_SCAN_ABORT
     - Patch 5 introduces oom timeout.
       https://jira.sw.ru/browse/PSBM-38581
     - Patch 6 makes oom fairer when it comes to selecting a victim among
       different containers.
       https://jira.sw.ru/browse/PSBM-37915
     - Patch 7 prepares oom for introducing berserker mode
     - Patch 8 resurrects oom berserker mode, which is supposed to cope with
       actively forking processes.
       https://jira.sw.ru/browse/PSBM-17930
    
    https://jira.sw.ru/browse/PSBM-26973
    
    Changes in v3:
     - rework oom_trylock (patch 3)
     - select exiting process instead of aborting oom scan so as not to keep
       busy-waiting for an exiting process to exit (patches 3, 4)
     - cleanup oom timeout handling + fix stuck process trace dumped
       multiple times on timeout (patch 5)
     - set max_overdraft to ULONG_MAX on selected processes (patch 6)
     - rework oom berserker process selection logic (patches 7, 8)
    
    Changes in v2:
     - s/time_after/time_after_eq to avoid BUG_ON in oom_trylock (patch 4)
     - propagate victim to the context that initiated oom in oom_unlock
       (patch 6)
     - always set oom_end on releasing oom context (patch 6)
    
    Vladimir Davydov (8):
      memcg: add mem_cgroup_get/put helpers
      memcg: add lock for protecting memcg->oom_notify list
      oom: rework locking design
      oom: introduce oom timeout
      oom: drop OOM_SCAN_ABORT
      oom: rework logic behind memory.oom_guarantee
      oom: pass points and overdraft to oom_kill_process
      oom: resurrect berserker mode
    
    Reviewed-by: Kirill Tkhai <ktkhai at odin.com>
    
    =========================================
    This patch description:
    
    Currently, memcg_oom_lock is used for this, but I'm going to get rid of
    it in the following patch, so introduce a dedicated lock.
    
    Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
---
 mm/memcontrol.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fdd14dd2..faef356 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5766,12 +5766,18 @@ static int compare_thresholds(const void *a, const void *b)
 	return 0;
 }
 
+static DEFINE_SPINLOCK(memcg_oom_notify_lock);
+
 static int mem_cgroup_oom_notify_cb(struct mem_cgroup *memcg)
 {
 	struct mem_cgroup_eventfd_list *ev;
 
+	spin_lock(&memcg_oom_notify_lock);
+
 	list_for_each_entry(ev, &memcg->oom_notify, list)
 		eventfd_signal(ev->eventfd, 1);
+
+	spin_unlock(&memcg_oom_notify_lock);
 	return 0;
 }
 
@@ -5957,7 +5963,7 @@ static int mem_cgroup_oom_register_event(struct cgroup *cgrp,
 	if (!event)
 		return -ENOMEM;
 
-	spin_lock(&memcg_oom_lock);
+	spin_lock(&memcg_oom_notify_lock);
 
 	event->eventfd = eventfd;
 	list_add(&event->list, &memcg->oom_notify);
@@ -5965,7 +5971,7 @@ static int mem_cgroup_oom_register_event(struct cgroup *cgrp,
 	/* already in OOM ? */
 	if (atomic_read(&memcg->under_oom))
 		eventfd_signal(eventfd, 1);
-	spin_unlock(&memcg_oom_lock);
+	spin_unlock(&memcg_oom_notify_lock);
 
 	return 0;
 }
@@ -5979,7 +5985,7 @@ static void mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
 
 	BUG_ON(type != _OOM_TYPE);
 
-	spin_lock(&memcg_oom_lock);
+	spin_lock(&memcg_oom_notify_lock);
 
 	list_for_each_entry_safe(ev, tmp, &memcg->oom_notify, list) {
 		if (ev->eventfd == eventfd) {
@@ -5988,7 +5994,7 @@ static void mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
 		}
 	}
 
-	spin_unlock(&memcg_oom_lock);
+	spin_unlock(&memcg_oom_notify_lock);
 }
 
 static int mem_cgroup_oom_control_read(struct cgroup *cgrp,