linux-kernel - Re: [PATCH 1/4] export __put_task

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Message-ID: <20070827181056.GA30176@sgi.com>
Date:	Mon, 27 Aug 2007 13:10:56 -0500
From:	Dean Nelson <dcn@....com>
To:	Al Viro <viro@....linux.org.uk>
Cc:	akpm@...ux-foundation.org, linux-ia64@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	tony.luck@...el.com, jes@....com
Subject: Re: [PATCH 1/4] export __put_task_struct for XPMEM

On Mon, Aug 27, 2007 at 05:13:28PM +0100, Al Viro wrote:
> On Mon, Aug 27, 2007 at 10:59:33AM -0500, Dean Nelson wrote:
> > This patch exports __put_task_struct as it is needed by XPMEM.
> > 
> > Signed-off-by: Dean Nelson <dcn@....com>
> > 
> > ---
> > 
> > One struct file_operations registered by XPMEM, xpmem_open(), calls
> > 'get_task_struct(current->group_leader)' and another, xpmem_flush(), calls
> > 'put_task_struct(tg->group_leader)'.
> 
> Does it?  Well, then open the file in question and start doing close(dup(fd))
> in a loop.  Won't take long for an oops...

Actually it won't oops. And that's because when the file is opened,
xpmem_open() creates a structure for that thread group, and when
xpmem_flush() is called on the close() it first looks for that structure
and if it finds it then it does what it needs to do (which includes the
put_task_struct() call) and then finishes off by destroying the structure.
So for subsequent closes xpmem_flush() returns without calling
put_task_struct().
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