[PATCH] mm/oom_kill: fix uninitialized oc->constraint

[Yafang Shao <laoar.shao@gmail.com>]

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:
[  133.078102] 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:
[  952.977946] oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),
cpuset=/,mems_allowed=0,oom_memcg=/foo,task_memcg=/foo,task=bash,pid=13681,uid=0

Fixes: ef8444ea01d7 ("mm, oom: reorganize the oom report in dump_header")
Cc: Wind Yu <yuzhoujian@didichuxing.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 mm/oom_kill.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5a58778..f719b64 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -987,8 +987,7 @@ 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;
@@ -998,7 +997,7 @@ 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 */
@@ -1035,7 +1034,6 @@ int unregister_oom_notifier(struct notifier_block *nb)
 bool out_of_memory(struct oom_control *oc)
 {
 	unsigned long freed = 0;
-	enum oom_constraint constraint = CONSTRAINT_NONE;
 
 	if (oom_killer_disabled)
 		return false;
@@ -1071,10 +1069,10 @@ 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) &&
-- 
1.8.3.1