On Tue, 8 Jun 2010, Andrew Morton wrote:
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -441,8 +441,11 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> > unsigned long points, struct mem_cgroup *mem,
> > const char *message)
> > {
> > + struct task_struct *victim = p;
> > struct task_struct *c;
> > struct task_struct *t = p;
> > + unsigned long victim_points = 0;
> > + struct timespec uptime;
> >
> > if (printk_ratelimit())
> > dump_header(p, gfp_mask, order, mem);
> > @@ -456,22 +459,30 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> > return 0;
> > }
> >
> > - printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
> > - message, task_pid_nr(p), p->comm, points);
> > + pr_err("%s: Kill process %d (%s) score %lu or sacrifice child\n",
> > + message, task_pid_nr(p), p->comm, points);
>
> fyi, access to another task's ->comm is racy against prctl(). Fixable
> with get_task_comm(). But that takes task_lock(), which is risky in
> this code. The world wouldn't end if we didn't fix this ;)
>
I'll look into doing that, thanks!
> > - /* Try to kill a child first */
> > + /* Try to sacrifice the worst child first */
> > + do_posix_clock_monotonic_gettime(&uptime);
> > do {
> > + unsigned long cpoints;
>
> This could be local to the list_for_each_entry() block.
>
Ok.
> What does "cpoints" mean?
>
child points :) I'll send an incremental patch.
> > list_for_each_entry(c, &t->children, sibling) {
>
> I'm surprised we don't have a sched.h helper for this. Maybe it's not
> a very common thing to do.
>
> > if (c->mm == p->mm)
> > continue;
> > if (mem && !task_in_mem_cgroup(c, mem))
> > continue;
> > - if (!oom_kill_task(c))
> > - return 0;
> > +
> > + /* badness() returns 0 if the thread is unkillable */
> > + cpoints = badness(c, uptime.tv_sec);
> > + if (cpoints > victim_points) {
> > + victim = c;
> > + victim_points = cpoints;
> > + }
> > }
> > } while_each_thread(p, t);
> >
> > - return oom_kill_task(p);
> > + return oom_kill_task(victim);
> > }
>
> And this function is secretly called under tasklist_lock, which is what
> pins *victim, yes?
>
All of the out_of_memory() helper functions are called under
tasklist_lock, which is what makes all these iterations safe.
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