[PATCH -mm 3/3] mm/oom_kill: fix the wrong task->mm == mm checks in

From: Oleg Nesterov
Date: Tue Sep 29 2015 - 10:22:01 EST


Both "child->mm == mm" and "p->mm != mm" checks in oom_kill_process()
are wrong. ->mm can be if task is the exited group leader. This means
in particular that "kill sharing same memory" loop can miss a process
with a zombie leader which uses the same ->mm.

Note: the process_has_mm(child, p->mm) check is still not 100% correct,
p->mm can be NULL too. This is minor, but probably deserves a fix or a
comment anyway.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
mm/oom_kill.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 8e7bed2..8ecac2ef 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -483,6 +483,17 @@ void oom_killer_enable(void)
oom_killer_disabled = false;
}

+static bool process_has_mm(struct task_struct *p, struct mm_struct *mm)
+{
+ struct task_struct *t;
+
+ for_each_thread(p, t)
+ if (t->mm)
+ return t->mm == mm;
+
+ return false;
+}
+
#define K(x) ((x) << (PAGE_SHIFT-10))
/*
* Must be called while holding a reference to p, which will be released upon
@@ -530,7 +541,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
list_for_each_entry(child, &t->children, sibling) {
unsigned int child_points;

- if (child->mm == p->mm)
+ if (process_has_mm(child, p->mm))
continue;
/*
* oom_badness() returns 0 if the thread is unkillable
@@ -588,7 +599,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
continue;
if (same_thread_group(p, victim))
continue;
- if (p->mm != mm)
+ if (!process_has_mm(p, mm))
continue;
if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
continue;
--
2.4.3

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