linux-kernel - Re: [PATCH 1/1] pid_ns: move pid_ns_release_proc() from proc_flush_task() to zap_pid_ns

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Date:	Wed, 23 Jun 2010 23:36:30 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Containers <containers@...ts.osdl.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [PATCH 1/1] pid_ns: move pid_ns_release_proc() from
	proc_flush_task() to zap_pid_ns_processes()

Oleg Nesterov [oleg@...hat.com] wrote:
| This is mostly cleanup and optimization, but also fixes the bug.
| 
| proc_flush_task() checks upid->nr == 1 to detect the case when
| a sub-namespace exits. However, this doesn't work in case when
| a multithreaded init execs and calls release_task(old_leader),
| the old leader has the same pid 1.
| 
| Move pid_ns_release_proc() to zap_pid_ns_processes(), it is called
| when we know for sure that init is exiting.

Hmm, I almost agreed, but have a question :-)

Yes, we know that the container-init is exiting. But if its parent (in
the parent ns) waits on it and calls release_task(), won't we call
proc_flush_task_mnt() on this container-init ? This would happen after
dropping the mnt in zap_pid_ns_processes() no ?

At the time zap_pid_ns_processes() is called, the container-init is still
not in EXIT_ZOMBIE state right ? (Or does your statement below include
EXIT_DEAD and EXIT_ZOMBIE tasks ?)

| 
| Note: with or without this change this mntput() can happen before the
| EXIT_DEAD tasks not visible to do_wait() have passed proc_flush_task().
| We need more fixes.
| 

Sukadev
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