linux-kernel - Re: [PATCH] ptrace: add ability to get clear_tid

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Message-ID: <20120203163025.GI11834@moon>
Date:	Fri, 3 Feb 2012 20:30:25 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Vagin <avagin@...nvz.org>, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] ptrace: add ability to get clear_tid_address

On Fri, Feb 03, 2012 at 08:25:19AM -0800, Tejun Heo wrote:
> On Fri, Feb 03, 2012 at 02:11:23PM +0300, Andrew Vagin wrote:
> > Zero is written at clear_tid_address, when the process exits.
> > This functionality is used by pthread_join().
> > 
> > sys_set_tid_address() changes this address for current task.
> > 
> > Before this patch clear_tid_address could not be got from user space.
> > I want to dump a full state of a task, so I need this address.
> > Also I think it may be useful for debugging a multithreading program.
> > 
> > I am not sure that ptrace is suitable place. It may be added in prctl,
> > but I think it's a bit useless and strange. I can't image a real
> > situation (avoid checkpointing) when a thread will want to get own
> > clear_tid_address from itself, this address is used by parent ussually.
> > 
> > Signed-off-by: Andrew Vagin <avagin@...nvz.org>
> 
> Ummm... this really doesn't fit in ptrace.  Cyrill, why not put it
> together with other params you're exporting?
> 

We could add it to /proc/pid/stat (but I fear Andrew Morton shoot me then ;)

	Cyrill
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