linux-kernel - Re: [PATCH] kernel: move exit_task_work() past exit

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Message-ID: <20130413142246.GA864@redhat.com>
Date:	Sat, 13 Apr 2013 16:22:46 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH] kernel: move exit_task_work() past exit_notify()

On 04/12, Andrey Vagin wrote:
> exit_task_work() must be called after exit_notify, because
> exit_task_namespaces() may release a file and fput() enqueues a work.
>
> exit_notify
>   exit_task_namespaces
>     free_ipc_ns
>       shm_destroy
>         fput
>           task_work_add
>
> so if task works don't run after exit_notify(), a few files may leak.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: David Howells <dhowells@...hat.com>
> Signed-off-by: Andrey Vagin <avagin@...nvz.org>
> ---
>  kernel/exit.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 60bc027..1d1129b 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -795,7 +795,6 @@ void do_exit(long code)
>  	exit_shm(tsk);
>  	exit_files(tsk);
>  	exit_fs(tsk);
> -	exit_task_work(tsk);
>  	check_stack_usage();
>  	exit_thread();
>
> @@ -822,6 +821,7 @@ void do_exit(long code)
>  	ptrace_put_breakpoints(tsk);
>
>  	exit_notify(tsk, group_dead);
> +	exit_task_work(tsk);

I am not comfortable with this change...

The task is "really dead" after exit_notify(), even release_task(current)
can be called.

Let me think a bit... It seems that we have the alternative.

Oleg.

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