linux-kernel - Re: [PATCH v3 20/20] signal: Don't restart fork when signals come in.

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Message-ID: <20180726162144.GC32718@redhat.com>
Date:   Thu, 26 Jul 2018 18:21:44 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Wen Yang <wen.yang99@....com.cn>, majiang <ma.jiang@....com.cn>
Subject: Re: [PATCH v3 20/20] signal: Don't restart fork when signals come in.

On 07/24, Eric W. Biederman wrote:
>
> Similarly the current code will also miss blocked
> signals that are delivered to multiple process, as those signals will
> not appear pending during fork.

Well, I still think this needs a separate change and discussion...

Let me repeat, I simply do not know if this is good or not, I don't know
if the current behaviour is by design or it is mistake.

OK, I won't argue but note that your patch doesn't really fix the problem,

> +	spin_lock_irq(&current->sighand->siglock);
> +	if (!(clone_flags & CLONE_THREAD))
> +		hlist_add_head(&delayed.node, &current->signal->multiprocess);
> +	recalc_sigpending();
> +	spin_unlock_irq(&current->sighand->siglock);
> +	retval = -ERESTARTNOINTR;
> +	if (signal_pending(current))
> +		goto fork_out;

because recalc_sigpending() will not notice the blocked multiprocess signal
if it is already pending.

Oleg.