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

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Message-ID: <20070125150542.GA27472@sergelap.austin.ibm.com>
Date:	Thu, 25 Jan 2007 09:05:42 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Cedric Le Goater <clg@...ibm.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: [PATCH] namespaces: fix race at task exit

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>

---

 kernel/exit.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

765277a4170d7bbd1c4613de661ec6ac64d5580a
diff --git a/kernel/exit.c b/kernel/exit.c
index 3540172..ab9ae30 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -174,6 +174,7 @@ repeat:
 	write_unlock_irq(&tasklist_lock);
 	proc_flush_task(p);
 	release_thread(p);
+	exit_task_namespaces(p);
 	call_rcu(&p->rcu, delayed_put_task_struct);
 
 	p = leader;
@@ -939,7 +940,6 @@ fastcall NORET_TYPE void do_exit(long co
 	tsk->exit_code = code;
 	proc_exit_connector(tsk);
 	exit_notify(tsk);
-	exit_task_namespaces(tsk);
 #ifdef CONFIG_NUMA
 	mpol_free(tsk->mempolicy);
 	tsk->mempolicy = NULL;
-- 
1.1.6
-
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