On 03/31, Oleg Nesterov wrote:
>
> OK, but I guess this !p->mm check is still wrong for the same reason.
> In fact I do not understand why it is needed in select_bad_process()
> right before oom_badness() which checks ->mm too (and this check is
> equally wrong).
Probably something like the patch below makes sense. Note that
"skip kernel threads" logic is wrong too, we should check PF_KTHREAD.
Probably it is better to check it in select_bad_process() instead,
near is_global_init().
The new helper, find_lock_task_mm(), should be used by
oom_forkbomb_penalty() too.
dump_tasks() doesn't need it, it does do_each_thread(). Cough,
__out_of_memory() and out_of_memory() call it without tasklist.
We are going to panic() anyway, but still.
Oleg.
--- x/mm/oom_kill.c
+++ x/mm/oom_kill.c
@@ -129,6 +129,19 @@ static unsigned long oom_forkbomb_penalt
(child_rss / sysctl_oom_forkbomb_thres) : 0;
}
+static find_lock_task_mm(struct task_struct *p)
+{
+ struct task_struct *t = p;
+ do {
+ task_lock(t);
+ if (likely(t->mm && !(t->flags & PF_KTHREAD)))
+ return t;
+ task_unlock(t);
+ } while_each_thred(p, t);
+
+ return NULL;
+}
+
/**
* oom_badness - heuristic function to determine which candidate task to kill
* @p: task struct of which task we should calculate
@@ -159,13 +172,9 @@ unsigned int oom_badness(struct task_str
if (p->flags & PF_OOM_ORIGIN)
return 1000;
- task_lock(p);
- mm = p->mm;
- if (!mm) {
- task_unlock(p);
+ p = find_lock_task_mm(p);
+ if (!p)
return 0;
- }
-
/*
* The baseline for the badness score is the proportion of RAM that each
* task's rss and swap space use.
@@ -330,12 +339,6 @@ static struct task_struct *select_bad_pr
*ppoints = 1000;
}
- /*
- * skip kernel threads and tasks which have already released
- * their mm.
- */
- if (!p->mm)
- continue;
if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
continue;
--
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