linux-kernel - Re: [PATCH RFC 09/13] exit: Use for_each_thread() in do

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Message-ID: <20150526194613.GC6978@redhat.com>
Date:	Tue, 26 May 2015 21:46:13 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kirill Tkhai <ktkhai@...n.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michal Hocko <mhocko@...e.cz>, Rik van Riel <riel@...hat.com>,
	Ionut Alexa <ionut.m.alexa@...il.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Kirill Tkhai <tkhai@...dex.ru>
Subject: Re: [PATCH RFC 09/13] exit: Use for_each_thread() in do_wait()

On 05/25, Kirill Tkhai wrote:
>
> Refactoring, no functionality change.

Hmm. unless I missed something this change is wrong.

> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1538,8 +1538,7 @@ static long do_wait(struct wait_opts *wo)
>  
>  	set_current_state(TASK_INTERRUPTIBLE);
>  	read_lock(&tasklist_lock);
> -	tsk = current;
> -	do {
> +	for_each_thread(current, tsk) {
>  		retval = do_wait_thread(wo, tsk);
>  		if (retval)
>  			goto end;
> @@ -1550,7 +1549,7 @@ static long do_wait(struct wait_opts *wo)
>  
>  		if (wo->wo_flags & __WNOTHREAD)
>  			break;
> -	} while_each_thread(current, tsk);
> +	}

Please note the __WNOTHREAD check. This is the rare case when we
actually want while_each_thread() (although it should die anyway).

for_each_thread() always starts from ->group_leader, but we need
to start from "current" first.

Oleg.

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