On 06/29, David Rientjes wrote:
>
> +/*
> + * Must be called while holding a reference to p, which will be released upon
> + * returning.
> + */
I am not really sure this is the most clean approach, see below...
> void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> unsigned int points, unsigned long totalpages,
> struct mem_cgroup *memcg, nodemask_t *nodemask,
> @@ -454,6 +462,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> */
> if (p->flags & PF_EXITING) {
> set_tsk_thread_flag(p, TIF_MEMDIE);
> + put_task_struct(p);
> return;
> }
>
> @@ -471,6 +480,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> * parent. This attempts to lose the minimal amount of work done while
> * still freeing memory.
> */
> + read_lock(&tasklist_lock);
> do {
> list_for_each_entry(child, &t->children, sibling) {
> unsigned int child_points;
> @@ -483,15 +493,26 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> child_points = oom_badness(child, memcg, nodemask,
> totalpages);
> if (child_points > victim_points) {
> + put_task_struct(victim);
> victim = child;
> victim_points = child_points;
> + get_task_struct(victim);
> }
> }
> } while_each_thread(p, t);
> + read_unlock(&tasklist_lock);
>
> - victim = find_lock_task_mm(victim);
> - if (!victim)
> + rcu_read_lock();
> + p = find_lock_task_mm(victim);
> + if (!p) {
> + rcu_read_unlock();
> + put_task_struct(victim);
> return;
> + } else if (victim != p) {
> + get_task_struct(p);
> + put_task_struct(victim);
> + victim = p;
> + }
>
> /* mm cannot safely be dereferenced after task_unlock(victim) */
> mm = victim->mm;
> @@ -522,9 +543,11 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> task_unlock(p);
> do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
> }
> + rcu_read_unlock();
>
> set_tsk_thread_flag(victim, TIF_MEMDIE);
> do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
> + put_task_struct(victim);
It seems to me we can avoid this get/put dance in oom_kill_process(),
just you need to extend the rcu-protected area. In this case the caller
of select_bad_process() does a single put_, and
sysctl_oom_kill_allocating_task doesn't need get_task_struct(current).
Look more clean/simple to me.
However. This is subjective, and I see nothing wrong in this patch,
I won't insist.
Looks correct.
Oleg.
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