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From: Kirill Tkhai <tkhai@yandex.ru>
To: Oleg Nesterov <oleg@redhat.com>, Kirill Tkhai <ktkhai@odin.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Michal Hocko <mhocko@suse.cz>, Rik van Riel <riel@redhat.com>,
        Ionut Alexa <ionut.m.alexa@gmail.com>,
        Peter Hurley <peter@hurleysoftware.com>
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Subject: Re: [PATCH RFC 09/13] exit: Use for_each_thread() in do_wait()
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27.05.2015, 12:34, "Kirill Tkhai" <tkhai@yandex.ru>:
> 26.05.2015, 22:47, "Oleg Nesterov" <oleg@redhat.com>:
>> šOn 05/25, Kirill Tkhai wrote:
>>> ššRefactoring, no functionality change.
>> šHmm. unless I missed something this change is wrong.
>>> šš--- a/kernel/exit.c
>>> šš+++ b/kernel/exit.c
>>> šš@@ -1538,8 +1538,7 @@ static long do_wait(struct wait_opts *wo)
>>>
>>> šššššššššššset_current_state(TASK_INTERRUPTIBLE);
>>> šššššššššššread_lock(&tasklist_lock);
>>> šš- tsk = current;
>>> šš- do {
>>> šš+ for_each_thread(current, tsk) {
>>> šššššššššššššššššššretval = do_wait_thread(wo, tsk);
>>> šššššššššššššššššššif (retval)
>>> šššššššššššššššššššššššššššgoto end;
>>> šš@@ -1550,7 +1549,7 @@ static long do_wait(struct wait_opts *wo)
>>>
>>> šššššššššššššššššššif (wo->wo_flags & __WNOTHREAD)
>>> šššššššššššššššššššššššššššbreak;
>>> šš- } while_each_thread(current, tsk);
>>> šš+ }
>> šPlease note the __WNOTHREAD check. This is the rare case when we
>> šactually want while_each_thread() (although it should die anyway).
>>
>> šfor_each_thread() always starts from ->group_leader, but we need
>> što start from "current" first.
>
> Sure, this must be like below. Thanks!
> I won't resend the whole series with only this one patch changed to
> do not bomb mail boxes. Waiting for the review.
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index a268093..e4963d3 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1538,8 +1538,10 @@ static long do_wait(struct wait_opts *wo)
>
> šššššššššset_current_state(TASK_INTERRUPTIBLE);
> šššššššššread_lock(&tasklist_lock);
> - tsk = current;
> - do {
> + for_each_thread(current, tsk) {
> + if (wo->wo_flags & __WNOTHREAD)
> + tsk = current;
> +
> šššššššššššššššššretval = do_wait_thread(wo, tsk);
> šššššššššššššššššif (retval)
> šššššššššššššššššššššššššgoto end;
> @@ -1550,7 +1552,7 @@ static long do_wait(struct wait_opts *wo)
>
> šššššššššššššššššif (wo->wo_flags & __WNOTHREAD)
> šššššššššššššššššššššššššbreak;
> - } while_each_thread(current, tsk);
> + }
> šššššššššread_unlock(&tasklist_lock);
>
> šnotask:

Hm. Once again. Is the problem in __WNOTHREAD only?
Should we firstly reap our own children in common case?