linux-kernel - Re: [PATCH 02/16] signal: fix CLD

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Message-ID: <20101220145815.GA11583@redhat.com>
Date:	Mon, 20 Dec 2010 15:58:15 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	roland@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	rjw@...k.pl, jan.kratochvil@...hat.com
Subject: Re: [PATCH 02/16] signal: fix CLD_CONTINUED notification target

On 12/06, Tejun Heo wrote:
>
> CLD_CONTINUED notification code calls do_notify_parent_cldstop() with
> its group_leader; however, do_notify_parent_cldstop() already uses the
> group_leader for non-ptraced notifications.

Yes,

> The duplicate
> ->group_leader dereferencing is unnecessary and leads to incorrectly
> notifying the group_leader's ptracer of CLD_CONTINUED from a different
> task in the group.  Fix it.

I do not really agree this is wrong, group_leader was used intentionally
for ptrace case.

There is no "correct" thread who should report CLD_CONTINUED, a random
thread wins and notifies its ->real_parent or debugger. If we always
choose ->group_leader, we always knows what happens. With this patch
we can't predict where does this notification go.

> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1867,7 +1867,7 @@ relock:
>
>  		if (why) {
>  			read_lock(&tasklist_lock);
> -			do_notify_parent_cldstop(current->group_leader, why);
> +			do_notify_parent_cldstop(current, why);

OTOH, I see nothing really wrong with this change, and this all will
be reworked by the next patches anyway.

Oleg.

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