On Wed 30-09-15 20:24:11, Oleg Nesterov wrote:
> 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 <o...@redhat.com>
Acked-by: Michal Hocko <mho...@suse.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
--
Michal Hocko
SUSE Labs
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