linux-kernel - Re: [PATCH 1/1] aio: change exit_aio() to load mm->ioctx_table once and avoid rcu_read

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Message-ID: <20140429230457.GA4604@mguzik.redhat.com>
Date:	Wed, 30 Apr 2014 01:04:58 +0200
From:	Mateusz Guzik <mguzik@...hat.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kent Overstreet <kmo@...erainc.com>,
	Al Viro <viro@...iv.linux.org.uk>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] aio: change exit_aio() to load mm->ioctx_table once
 and avoid rcu_read_lock()

On Tue, Apr 29, 2014 at 05:22:22PM -0400, Benjamin LaHaise wrote:
> On Tue, Apr 29, 2014 at 04:42:17PM -0400, Benjamin LaHaise wrote:
> > > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> > 
> > Your patch does not apply because it is whitespace damaged.  Please resend 
> > and verify that it applies with 'git am'.
> 
> Whoops, it's not whitespace damange, but rather that it doesn't apply with 
> the other changes that are queued up in the aio-next tree.  You can find a 
> copy of that tree at git://git.kvack.org/~bcrl/aio-next.git .  The change 
> that conflicts is an additional parameter to kill_ioctx().

While here is there any reason for:
rcu_assign_pointer(mm->ioctx_table, NULL);

Nothing looks at this pointer afterwards and mm is about to be freed.

I thought it would be used to sanity check that everything was cleared
before freeing, but that is nod one and not every pointer is nullified
anyway.

-- 
Mateusz Guzik
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