memcg: avoid oom-killing innocent task in case of use_hierarchy

task_in_mem_cgroup(), which is called by select_bad_process() to check
whether a task can be a candidate for being oom-killed from memcg's limit,
checks "curr->use_hierarchy"("curr" is the mem_cgroup the task belongs
to).

But this check return true(it's false positive) when:

	<some path>/aa		use_hierarchy == 0	<- hitting limit
	  <some path>/aa/00	use_hierarchy == 1	<- the task belongs to

This leads to killing an innocent task in aa/00.  This patch is a fix for
this bug.  And this patch also fixes the arg for
mem_cgroup_print_oom_info().  We should print information of mem_cgroup
which the task being killed, not current, belongs to.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 15 insertions, 8 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6273984f2e34..a294b7576070 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -760,7 +760,13 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
         task_unlock(task);
         if (!curr)
                 return 0;
-        if (curr->use_hierarchy)
+        /*
+         * We should check use_hierarchy of "mem" not "curr". Because checking
+         * use_hierarchy of "curr" here make this function true if hierarchy is
+         * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
+         * hierarchy(even if use_hierarchy is disabled in "mem").
+         */
+        if (mem->use_hierarchy)
                 ret = css_is_ancestor(&curr->css, &mem->css);
         else
                 ret = (curr == mem);
@@ -1009,7 +1015,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
         static char memcg_name[PATH_MAX];
         int ret;
 
-        if (!memcg)
+        if (!memcg || !p)
                 return;
 
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 25c679e0288a..f52481b1c1e5 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -356,7 +356,8 @@ static void dump_tasks(const struct mem_cgroup *mem)
         } while_each_thread(g, p);
 }
 
-static void dump_header(gfp_t gfp_mask, int order, struct mem_cgroup *mem)
+static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
+                                                        struct mem_cgroup *mem)
 {
         pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "
                 "oom_adj=%d\n",
@@ -365,7 +366,7 @@ static void dump_header(gfp_t gfp_mask, int order, struct mem_cgroup *mem)
         cpuset_print_task_mems_allowed(current);
         task_unlock(current);
         dump_stack();
-        mem_cgroup_print_oom_info(mem, current);
+        mem_cgroup_print_oom_info(mem, p);
         show_mem();
         if (sysctl_oom_dump_tasks)
                 dump_tasks(mem);
@@ -440,7 +441,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
         struct task_struct *c;
 
         if (printk_ratelimit())
-                dump_header(gfp_mask, order, mem);
+                dump_header(p, gfp_mask, order, mem);
 
         /*
          * If the task is already exiting, don't alarm the sysadmin or kill
@@ -576,7 +577,7 @@ retry:
         /* Found nothing?!?! Either we hang forever, or we panic. */
         if (!p) {
                 read_unlock(&tasklist_lock);
-                dump_header(gfp_mask, order, NULL);
+                dump_header(NULL, gfp_mask, order, NULL);
                 panic("Out of memory and no killable processes...\n");
         }
 
@@ -644,7 +645,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
                 return;
 
         if (sysctl_panic_on_oom == 2) {
-                dump_header(gfp_mask, order, NULL);
+                dump_header(NULL, gfp_mask, order, NULL);
                 panic("out of memory. Compulsory panic_on_oom is selected.\n");
         }
 
@@ -663,7 +664,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 
         case CONSTRAINT_NONE:
                 if (sysctl_panic_on_oom) {
-                        dump_header(gfp_mask, order, NULL);
+                        dump_header(NULL, gfp_mask, order, NULL);
                         panic("out of memory. panic_on_oom is selected\n");
                 }
                 /* Fall-through */