Re: [RFC,PATCH] Use RCU to protect tasklist for unicast signals

[Oleg Nesterov <oleg@tv-sign.ru>]

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.
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