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

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Message-ID: <20100623203735.GB25298@redhat.com>
Date:	Wed, 23 Jun 2010 22:37:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Louis Rilling <louis.rilling@...labs.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] pid_ns: move pid_ns_release_proc() from
	proc_flush_task() to zap_pid_ns_processes()

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.

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.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---

 fs/proc/base.c         |    4 ----
 kernel/pid_namespace.c |    2 ++
 2 files changed, 2 insertions(+), 4 deletions(-)

--- 35-rc3/fs/proc/base.c~PNS_5_MOVE_MNTPUT_TO_ZAP	2010-06-23 22:06:01.000000000 +0200
+++ 35-rc3/fs/proc/base.c	2010-06-23 22:10:26.000000000 +0200
@@ -2745,10 +2745,6 @@ void proc_flush_task(struct task_struct 
 		proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
 					tgid->numbers[i].nr);
 	}
-
-	upid = &pid->numbers[pid->level];
-	if (upid->nr == 1)
-		pid_ns_release_proc(upid->ns);
 }
 
 static struct dentry *proc_pid_instantiate(struct inode *dir,
--- 35-rc3/kernel/pid_namespace.c~PNS_5_MOVE_MNTPUT_TO_ZAP	2010-06-23 22:13:07.000000000 +0200
+++ 35-rc3/kernel/pid_namespace.c	2010-06-23 22:13:55.000000000 +0200
@@ -189,6 +189,8 @@ void zap_pid_ns_processes(struct pid_nam
 	} while (rc != -ECHILD);
 
 	acct_exit_ns(pid_ns);
+	pid_ns_release_proc(pid_ns);
+
 	return;
 }
 

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