mm/oom_kill.c: fix uninitialized oc->constraint

mainline inclusion
from mainline-5.2-rc7
commit 432b1de0
category: bugfix
bugzilla: 34611
CVE: NA

-------------------------------------------------
In dump_oom_summary() oc->constraint is used to show oom_constraint_text,
but it hasn't been set before.  So the value of it is always the default
value 0.  We should inititialize it before.

Bellow is the output when memcg oom occurs,

before this patch:
  oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null), cpuset=/,mems_allowed=0,oom_memcg=/foo,task_memcg=/foo,task=bash,pid=7997,uid=0

after this patch:
  oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null), cpuset=/,mems_allowed=0,oom_memcg=/foo,task_memcg=/foo,task=bash,pid=13681,uid=0

Link: http://lkml.kernel.org/r/1560522038-15879-1-git-send-email-laoar.shao@gmail.com
Fixes: ef8444ea ("mm, oom: reorganize the oom report in dump_header")
Signed-off-by: NYafang Shao <laoar.shao@gmail.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Wind Yu <yuzhoujian@didichuxing.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 432b1de0)
Signed-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/oom_kill.c

@@ -1026,8 +1026,7 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 /*
  * Determines whether the kernel must panic because of the panic_on_oom sysctl.
  */
-static void check_panic_on_oom(struct oom_control *oc,
-			       enum oom_constraint constraint)
+static void check_panic_on_oom(struct oom_control *oc)
 {
 	if (likely(!sysctl_panic_on_oom))
 		return;
@@ -1037,7 +1036,7 @@ static void check_panic_on_oom(struct oom_control *oc,
 		 * does not panic for cpuset, mempolicy, or memcg allocation
 		 * failures.
 		 */
-		if (constraint != CONSTRAINT_NONE)
+		if (oc->constraint != CONSTRAINT_NONE)
 			return;
 	}
 	/* Do not panic for oom kills triggered by sysrq */
@@ -1114,7 +1113,6 @@ EXPORT_SYMBOL_GPL(unregister_hisi_oom_notifier);
 bool out_of_memory(struct oom_control *oc)
 {
 	unsigned long freed = 0;
-	enum oom_constraint constraint = CONSTRAINT_NONE;
 #ifdef CONFIG_ASCEND_OOM
 	unsigned long oom_type;
 #endif
@@ -1168,10 +1166,10 @@ bool out_of_memory(struct oom_control *oc)
 	 * Check if there were limitations on the allocation (only relevant for
 	 * NUMA and memcg) that may require different handling.
 	 */
-	constraint = constrained_alloc(oc);
-	if (constraint != CONSTRAINT_MEMORY_POLICY)
+	oc->constraint = constrained_alloc(oc);
+	if (oc->constraint != CONSTRAINT_MEMORY_POLICY)
 		oc->nodemask = NULL;
-	check_panic_on_oom(oc, constraint);
+	check_panic_on_oom(oc);
 
 	if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
 	    current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&