Date: Mon, 23 Jun 2008 13:40:37 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: ebiederm@xmission.com, mingo@elte.hu, torvalds@linux-foundation.org,
       roland@redhat.com, linux-kernel@vger.kernel.org,
       "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [PATCH 1/3] introduce PF_KTHREAD flag
Message-Id: <20080623134037.8566f651.akpm@linux-foundation.org>
In-Reply-To: <20080601153042.GA8238@tv-sign.ru>
References: <20080601153042.GA8238@tv-sign.ru>
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On Sun, 1 Jun 2008 19:30:42 +0400
Oleg Nesterov <oleg@tv-sign.ru> wrote:

> Introduce the new PF_KTHREAD flag to mark the kernel threads. It is set by
> INIT_TASK() and copied to the forked childs (we could set it in kthreadd()
> along with PF_NOFREEZE instead).
> 
> daemonize() was changed as well. In that case testing of PF_KTHREAD is racy,
> but daemonize() is hopeless anyway.
> 
> This flag is cleared in do_execve(), before search_binary_handler(). Probably
> not the best place, we can do this in exec_mmap() or in start_thread(), or
> clear it along with PF_FORKNOEXEC. But I think this doesn't matter in practice,
> and if do_execve() fails kthread should die soon.
> 
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
> 
>  include/linux/sched.h     |    1 +
>  include/linux/init_task.h |    2 +-
>  kernel/exit.c             |    2 +-
>  fs/exec.c                 |    1 +
>  4 files changed, 4 insertions(+), 2 deletions(-)
> 
> --- 26-rc2/include/linux/sched.h~2_MAKE_PF_KTHREAD	2008-05-18 15:44:16.000000000 +0400
> +++ 26-rc2/include/linux/sched.h	2008-05-18 20:08:13.000000000 +0400
> @@ -1508,6 +1508,7 @@ static inline void put_task_struct(struc
>  #define PF_MEMPOLICY	0x10000000	/* Non-default NUMA mempolicy */
>  #define PF_MUTEX_TESTER	0x20000000	/* Thread belongs to the rt mutex tester */
>  #define PF_FREEZER_SKIP	0x40000000	/* Freezer should not count it as freezeable */
> +#define PF_KTHREAD	0x80000000	/* I am a kernel thread */

Well "Freezer: Introduce PF_FREEZER_NOSIG" has cheerily come in
afterwards and stolen 0x80000000 from us.  I'll redo this patch to use,
umm, 0x00000020.  Please check that this is OK (if it isn't someone
needs thwapping for not adding a dont-use-this comment).

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