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Date: Fri, 12 Aug 2005 12:51:17 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
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To: paulmck@us.ibm.com
Cc: Ingo Molnar <mingo@elte.hu>, Dipankar Sarma <dipankar@in.ibm.com>,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC,PATCH] Use RCU to protect tasklist for unicast signals
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Paul E. McKenney wrote:
>
> --- linux-2.6.13-rc4-realtime-preempt-V0.7.53-01/fs/exec.c	2005-08-11 11:44:55.000000000 -0700
> +++ linux-2.6.13-rc4-realtime-preempt-V0.7.53-01-tasklistRCU/fs/exec.c	2005-08-11 12:26:45.000000000 -0700
> [ ... snip ... ]
> @@ -785,11 +787,13 @@ no_thread_group:
>  		recalc_sigpending();
> 
> +		oldsighand->deleted = 1;
> +		oldsighand->successor = newsighand;

I don't think this is correct.

This ->oldsighand can be shared with another CLONE_SIGHAND
process and will not be deleted, just unshared.

When the signal is sent to that process we must use ->oldsighand
for locking, not the oldsighand->successor == newsighand.

Oleg.