linux-kernel - Re: [PATCH 4/6] signal: sigprocmask() should do retarget_shared

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Message-ID: <20110412130734.40166236@mfleming-mobl1.ger.corp.intel.com>
Date:	Tue, 12 Apr 2011 13:07:34 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nikita V. Youshchenko" <nyoushchenko@...sta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] signal: sigprocmask() should do
 retarget_shared_pending()

On Mon, 11 Apr 2011 19:21:37 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> In short, almost every changing of current->blocked is wrong, or at least
> can lead to the unexpected results.
> 
> For example. Two threads T1 and T2, T1 sleeps in sigtimedwait/pause/etc.
> kill(tgid, SIG) can pick T2 for TIF_SIGPENDING. If T2 calls sigprocmask()
> and blocks SIG before it notices the pending signal, nobody else can handle
> this pending shared signal.
> 
> I am not sure this is bug, but at least this looks strange imho. T1 should
> not sleep forever, there is a signal which should wake it up.

Agreed.

> @@ -2131,6 +2131,11 @@ int sigprocmask(int how, sigset_t *set, 
>  	}
>  
>  	spin_lock_irq(&tsk->sighand->siglock);
> +	if (signal_pending(tsk) && !thread_group_empty(tsk)) {
> +		sigset_t not_newblocked;
> +		signorsets(&not_newblocked, &current->blocked, &newset);
> +		retarget_shared_pending(tsk, &not_newblocked);
> +	}
>  	tsk->blocked = newset;
>  	recalc_sigpending();
>  	spin_unlock_irq(&tsk->sighand->siglock);

Oh man, that took me a while to understand.

So we're only retargetting the signals that we just blocked? That makes
sense but would you mind adding a comment?

-- 
Matt Fleming, Intel Open Source Technology Center
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