linux-kernel - Re: [PATCH] handle_stop_signal: don't wake up the stopped task until it sees SIGCONT

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Message-ID: <Pine.LNX.4.64.0802281756010.3391@jikos.suse.cz>
Date:	Thu, 28 Feb 2008 17:56:31 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	Roland McGrath <roland@...hat.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] handle_stop_signal: don't wake up the stopped task until
 it sees SIGCONT

On Thu, 28 Feb 2008, Oleg Nesterov wrote:

> -------------------------------------------------------------------------------
> [PATCH] handle_stop_signal: don't wake up the stopped task until it sees SIGCONT
> 
> The bug was found by Jiri Kosina <jkosina@...e.cz>, and the patch is based
> on his ideas.
> handle_stop_signal(SIGCONT) wakes up the stopped task and unlocks ->siglock
> for do_notify_parent_cldstop(p, CLD_CONTINUED). The woken task returns from
> do_signal_stop(), takes ->siglock and resumes to user-space without actually
> seeing SIGCONT which may have a handler.
> Move the code realated to do_notify_parent_cldstop(CLD_CONTINUED) up, before
> "wake_up_state(t, state)".
> NOTE: It is possible that the subsequent rm_from_queue(SIG_KERNEL_STOP_MASK)
> removes SIGSTOP which comes after SIGCONT when we drop ->siglock. Not nice,
> but possible even without this change. Hopefully we can remove the parent
> notifying code from the sender path completely, but this needs more thinking.
> Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

Acked-by: Jiri Kosina <jkosina@...e.cz>

-- 
Jiri Kosina
SUSE Labs
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