oom: dump_tasks() use find_lock_task_mm() too

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From: KOSAKI Motohiro on 2 Jun 2010 10:00

---

> dump_task() should have the same process iteration logic as
> select_bad_process().
>
> It is needed for protecting from task exiting race.
>
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com>

sorry, this patch made one warning.
incremental patch is here.



Signed-off-by: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com>
---
mm/oom_kill.c | 2 --
1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index b06f8d1..f33a1b8 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -334,8 +334,6 @@ static void dump_tasks(const struct mem_cgroup *mem)
"name\n");

for_each_process(p) {
- struct mm_struct *mm;
-
if (is_global_init(p) || (p->flags & PF_KTHREAD))
continue;
if (mem && !task_in_mem_cgroup(p, mem))
--
1.6.5.2



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From: Minchan Kim on 2 Jun 2010 11:10

---

Hi, Kosaki.

On Tue, Jun 01, 2010 at 02:51:49PM +0900, KOSAKI Motohiro wrote:
> dump_task() should have the same process iteration logic as
> select_bad_process().
>
> It is needed for protecting from task exiting race.
>
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com>
> ---
> mm/oom_kill.c | 31 +++++++++++++------------------
> 1 files changed, 13 insertions(+), 18 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index cbad4d4..a8af9e8 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -344,35 +344,30 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> */
> static void dump_tasks(const struct mem_cgroup *mem)
> {
> - struct task_struct *g, *p;
> + struct task_struct *p;
> + struct task_struct *task;
>
> printk(KERN_INFO "[ pid ] uid tgid total_vm rss cpu oom_adj "
> "name\n");
> - do_each_thread(g, p) {
> +
> + for_each_process(p) {
> struct mm_struct *mm;
>
> - if (mem && !task_in_mem_cgroup(p, mem))
> + if (is_global_init(p) || (p->flags & PF_KTHREAD))

select_bad_process needs is_global_init check to not select init as victim.
But in this case, it is just for dumping information of tasks.

> continue;
> - if (!thread_group_leader(p))
> + if (mem && !task_in_mem_cgroup(p, mem))
> continue;
>
> - task_lock(p);
> - mm = p->mm;
> - if (!mm) {
> - /*
> - * total_vm and rss sizes do not exist for tasks with no
> - * mm so there's no need to report them; they can't be
> - * oom killed anyway.
> - */

Please, do not remove the comment for mm newbies unless you think it's useless.

> - task_unlock(p);
> + task = find_lock_task_mm(p);
> + if (!task)
> continue;
> - }
> +
> printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d %3d %s\n",
> - p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
> - get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
> + task->pid, __task_cred(task)->uid, task->tgid, task->mm->total_vm,
> + get_mm_rss(task->mm), (int)task_cpu(task), task->signal->oom_adj,
> p->comm);
> - task_unlock(p);
> - } while_each_thread(g, p);
> + task_unlock(task);
> + }
> }
>
> static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> --
> 1.6.5.2
>
>
>
> --
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--
Kind regards,
Minchan Kim
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From: KOSAKI Motohiro on 2 Jun 2010 20:10

---

Hi

> > @@ -344,35 +344,30 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> > */
> > static void dump_tasks(const struct mem_cgroup *mem)
> > {
> > - struct task_struct *g, *p;
> > + struct task_struct *p;
> > + struct task_struct *task;
> >
> > printk(KERN_INFO "[ pid ] uid tgid total_vm rss cpu oom_adj "
> > "name\n");
> > - do_each_thread(g, p) {
> > +
> > + for_each_process(p) {
> > struct mm_struct *mm;
> >
> > - if (mem && !task_in_mem_cgroup(p, mem))
> > + if (is_global_init(p) || (p->flags & PF_KTHREAD))
>
> select_bad_process needs is_global_init check to not select init as victim.
> But in this case, it is just for dumping information of tasks.

But dumping oom unrelated process is useless and making confusion.
Do you have any suggestion? Instead, adding unkillable field?


>
> > continue;
> > - if (!thread_group_leader(p))
> > + if (mem && !task_in_mem_cgroup(p, mem))
> > continue;
> >
> > - task_lock(p);
> > - mm = p->mm;
> > - if (!mm) {
> > - /*
> > - * total_vm and rss sizes do not exist for tasks with no
> > - * mm so there's no need to report them; they can't be
> > - * oom killed anyway.
> > - */
>
> Please, do not remove the comment for mm newbies unless you think it's useless.

How is this?

task = find_lock_task_mm(p);
if (!task)
/*
* Probably oom vs task-exiting race was happen and ->mm
* have been detached. thus there's no need to report them;
* they can't be oom killed anyway.
*/
continue;



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From: Minchan Kim on 2 Jun 2010 20:40

---

On Thu, Jun 3, 2010 at 9:06 AM, KOSAKI Motohiro
<kosaki.motohiro(a)jp.fujitsu.com> wrote:
> Hi
>
>> > @@ -344,35 +344,30 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
>> >   */
>> >  static void dump_tasks(const struct mem_cgroup *mem)
>> >  {
>> > -   struct task_struct *g, *p;
>> > +   struct task_struct *p;
>> > +   struct task_struct *task;
>> >
>> >     printk(KERN_INFO "[ pid ]   uid  tgid total_vm      rss cpu oom_adj "
>> >            "name\n");
>> > -   do_each_thread(g, p) {
>> > +
>> > +   for_each_process(p) {
>> >             struct mm_struct *mm;
>> >
>> > -           if (mem && !task_in_mem_cgroup(p, mem))
>> > +           if (is_global_init(p) || (p->flags & PF_KTHREAD))
>>
>> select_bad_process needs is_global_init check to not select init as victim.
>> But in this case, it is just for dumping information of tasks.
>
> But dumping oom unrelated process is useless and making confusion.
> Do you have any suggestion? Instead, adding unkillable field?

I think it's not unrelated. Of course, init process doesn't consume
lots of memory but might consume more memory than old as time goes by
or some BUG although it is unlikely.

I think whether we print information of init or not isn't a big deal.
But we have been done it until now and you are trying to change it.
At least, we need some description why you want to remove it.
Making confusion? Hmm.. I don't think it make many people confusion.

>
>
>>
>> >                     continue;
>> > -           if (!thread_group_leader(p))
>> > +           if (mem && !task_in_mem_cgroup(p, mem))
>> >                     continue;
>> >
>> > -           task_lock(p);
>> > -           mm = p->mm;
>> > -           if (!mm) {
>> > -                   /*
>> > -                    * total_vm and rss sizes do not exist for tasks with no
>> > -                    * mm so there's no need to report them; they can't be
>> > -                    * oom killed anyway.
>> > -                    */
>>
>> Please, do not remove the comment for mm newbies unless you think it's useless.
>
> How is this?
>
>               task = find_lock_task_mm(p);
>               if (!task)
>                        /*
>                         * Probably oom vs task-exiting race was happen and ->mm
>                         * have been detached. thus there's no need to report them;
>                         * they can't be oom killed anyway.
>                         */
>                        continue;
>

Looks good to adding story about racing. but my point was "total_vm
and rss sizes do not exist for tasks with no mm". But I don't want to
bother you due to trivial.
It depends on you. :)

Thanks, Kosaki.


--
Kind regards,
Minchan Kim
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From: Minchan Kim on 2 Jun 2010 20:50

---

On Thu, Jun 3, 2010 at 9:41 AM, KOSAKI Motohiro
<kosaki.motohiro(a)jp.fujitsu.com> wrote:
>> On Thu, Jun 3, 2010 at 9:06 AM, KOSAKI Motohiro
>> <kosaki.motohiro(a)jp.fujitsu.com> wrote:
>> >> > -           mm = p->mm;
>> >> > -           if (!mm) {
>> >> > -                   /*
>> >> > -                    * total_vm and rss sizes do not exist for tasks with no
>> >> > -                    * mm so there's no need to report them; they can't be
>> >> > -                    * oom killed anyway.
>> >> > -                    */
>> >>
>> >> Please, do not remove the comment for mm newbies unless you think it's useless.
>> >
>> > How is this?
>> >
>> >               task = find_lock_task_mm(p);
>> >               if (!task)
>> >                        /*
>> >                         * Probably oom vs task-exiting race was happen and ->mm
>> >                         * have been detached. thus there's no need to report them;
>> >                         * they can't be oom killed anyway.
>> >                         */
>> >                        continue;
>> >
>>
>> Looks good to adding story about racing. but my point was "total_vm
>> and rss sizes do not exist for tasks with no mm". But I don't want to
>> bother you due to trivial.
>> It depends on you. :)
>
>
> old ->mm check have two intention.
>
>   a) the task is kernel thread?
>   b) the task have alredy detached ->mm
> but a) is not strictly correct check because we should think use_mm().
> therefore we appended PF_KTHREAD check. then, here find_lock_task_mm()
> focus exiting race, I think.
>

No objection.

--
Kind regards,
Minchan Kim
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