[PATCH v2] mm, oom: show process exiting information in __oom_kill_process()

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

When the OOM killer finding a victim and trying to kill it, if the victim
is already exiting, the task mm will be NULL and no process will be killed.
But the dump_header() has been already executed, so it will be strange to
dump so many information without killing a process. We'd better show some
helpful information to indicate why this happens.

Suggested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Qian Cai <cai@lca.pw>

---
v1 -> v2:
- improve the output, per Tetsuo and Michal
---
 mm/oom_kill.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 6e94962893ee..c176c988c109 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -863,6 +863,8 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
 
 	p = find_lock_task_mm(victim);
 	if (!p) {
+		pr_info("%s: OOM victim %d (%s) is already exiting. Skip killing the task\n",
+			message, task_pid_nr(victim), victim->comm);
 		put_task_struct(victim);
 		return;
 	} else if (victim != p) {
-- 
2.18.1