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Subject[PATCH -mm v2 3/3] mm/oom_kill: fix the wrong task->mm == mm checks in oom_kill_process()
Both "child->mm == mm" and "p->mm != mm" checks in oom_kill_process()
are wrong. task->mm can be NULL if the 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@redhat.com>
---
mm/oom_kill.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c189ee5..034d219 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -483,6 +483,18 @@ void oom_killer_enable(void)
oom_killer_disabled = false;
}

+static bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
+{
+ struct task_struct *t;
+
+ for_each_thread(p, t) {
+ struct mm_struct *t_mm = READ_ONCE(t->mm);
+ 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 +542,7 @@ 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_shares_mm(child, p->mm))
continue;
/*
* oom_badness() returns 0 if the thread is unkillable
@@ -584,7 +596,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
*/
rcu_read_lock();
for_each_process(p) {
- if (p->mm != mm)
+ if (!process_shares_mm(p, mm))
continue;
if (same_thread_group(p, victim))
continue;
--
2.4.3


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