linux-kernel - migrate_dead_tasks() vs sleep-after-exit

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Message-ID: <20070512145919.GC98@tv-sign.ru>
Date:	Sat, 12 May 2007 18:59:19 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Ingo Molnar <mingo@...e.hu>, "Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ego@...ibm.com, Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: migrate_dead_tasks() vs sleep-after-exit_notify() problems?

On 05/12, Oleg Nesterov wrote:
> 
> 	exit_notify()   ->exit_state != 0, and perhaps the task disappears
> 	                  from global process list

This, btw, means that do_exit()->__free_pipe_info() is not cpu-hotplug friendly.

The task may sleep on mutex_lock(->i_mutex), and dequeued from rq->arrays[].

The parent reaps this task, or it was TASK_DEAD and reaped itself.

CPU_DEAD comes, migration_call(CPU_DEAD) can do nothing with this task:

	- we already did release_task()->__unhash_process(), so
	  migrate_live_tasks() can't see it

	- migrate_dead_tasks() can't see it because it was deactivated.

No?

probably __might_sleep() should also check __exit_state.

Oleg.

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