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Date: Mon, 7 May 2012 16:56:47 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
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        Cyrill Gorcunov <gorcunov@openvz.org>,
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        Mike Galbraith <efault@gmx.de>, Christoph Hellwig <hch@infradead.org>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] vfs: Speed up deactivate_super for non-modular
 filesystems
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On Mon, May 07, 2012 at 11:17:06PM +0100, Al Viro wrote:
> On Mon, May 07, 2012 at 02:51:08PM -0700, Eric W. Biederman wrote:
> 
> > /proc and similar non-modular filesystems do not need a rcu_barrier
> > in deactivate_locked_super.  Being non-modular there is no danger
> > of the rcu callback running after the module is unloaded.
> 
> There's more than just a module unload there, though - actual freeing
> struct super_block also happens past that rcu_barrier()...

Is there anything in there for which synchronous operation is required?
If not, one approach would be to drop the rcu_barrier() calls to a
workqueue or something similar.

							Thanx, Paul