linux-kernel - Re: [PATCH] namespaces: fix race at task exit

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Message-ID: <45B8CAB7.9050402@fr.ibm.com>
Date:	Thu, 25 Jan 2007 16:20:23 +0100
From:	Cedric Le Goater <clg@...ibm.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
CC:	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Daniel Hokka Zakrisson <daniel@...ac.com>,
	herbert@...hfloor.at, akpm@...l.org, trond.myklebust@....uio.no,
	Linux Containers <containers@...ts.osdl.org>
Subject: Re: [PATCH] namespaces: fix race at task exit

Serge E. Hallyn wrote:
> In do_exit(), the exit_task_namespaces() was placed after
> exit_notify() because exit_notify ends up using the pid
> namespace both to access the reaper, and for detaching the
> pid.  However, this placement allows an nfs server to reap
> the task before exit_task_namespaces() completes.
> 
> This patch moves the exit_task_namespaces() into release_task,
> below release_thread() which puts the pids(), and just above
> the call_rcu(delayed_put_task_struct).  I believe this should
> solve both problems.
> 
> Signed-off-by: Serge E. Hallyn <serue@...ibm.com>

I've run some tests on x86 and x86_64: mounted a NFS share after 
having unshare(CLONE_NEWNS) and I didn't reproduce the bug Daniel 
had found. 

it looks safe.

C.
 

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