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Date: Mon, 18 Nov 2013 19:22:07 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Ian Kent <raven@themaw.net>
Cc: akpm@linux-foundation.org, sukadev@us.ibm.com, ebiederm@xmission.com,
        mszeredi@suse.cz, serge.hallyn@canonical.com,
        linux-kernel@vger.kernel.org
Subject: Re: [patch 1/2] autofs4: allow autofs to work outside the initial
	PID namespace
Message-ID: <20131118182207.GA12569@redhat.com>
References: <20131115222222.6F70A1CA1A1@corp2gmr1-1.eem.corp.google.com> <20131116160334.GA19309@redhat.com> <1384743883.2380.23.camel@perseus.fritz.box>
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On 11/18, Ian Kent wrote:
>
> It might be sufficient to surround the contents of show_options() with a
> lock on wq_mutex and update the check at the top to
>
> "lock; if (!sbi || sbi->catatonic) {unlock, return 0; } ..."

Or perhaps you can add synchronize_rcu() after swap(oz_pgrp, new_pid),
then show_options() can use rcu_read_lock().

This makes me think that we want put_pid_rcu() but I do not see a
simple way to implement it without synchronize_rcu or kmalloc...

Oleg.