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From: John Baldwin <jhb@freebsd.org>
To: Mateusz Guzik <mjg@freebsd.org>
Subject: Re: svn commit: r272596 - head/sys/fs/devfs
Date: Mon, 06 Oct 2014 11:37:32 -0400
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On Monday, October 06, 2014 06:20:36 AM Mateusz Guzik wrote:
> Author: mjg
> Date: Mon Oct  6 06:20:35 2014
> New Revision: 272596
> URL: https://svnweb.freebsd.org/changeset/base/272596
> 
> Log:
>   devfs: don't take proctree_lock unconditionally in devfs_close
> 
>   MFC after:	1 week

Just for my sanity:

What keeps td->td_proc->p_session static in this case so that it is safe to 
dereference it?  Specifically, if you are preempted after reading p_session 
but before you then read s_ttyvp, what prevents a race with another thread 
changing the session of td->td_proc?

-- 
John Baldwin