linux-kernel - Re: [PATCH] copy_process: remove the unneeded clear_tsk_thread_flag(TIF

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Message-ID: <20090428124730.GA17868@redhat.com>
Date:	Tue, 28 Apr 2009 14:47:30 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] copy_process: remove the unneeded
	clear_tsk_thread_flag(TIF_SIGPENDING)

On 04/27, Roland McGrath wrote:
>
> Acked-by: Roland McGrath <roland@...hat.com>
>
> > The forked child can have TIF_SIGPENDING if it was copied from parent's
> > ti->flags. But this is harmless and actually almost never happens, because
> > copy_process() can't succeed if signal_pending() == T.
>
> When it does happen, it's actually improper to clear it.  In a CLONE_THREAD
> case, the pending signals might include shared_pending signals that the
> child too should take.  (Arguably there is no way to notice, since the
> parent thread will be racing to dequeue the same signals.)

Yes, sure. Now I see the changelog is not very clear.

I meant, it is possible that the parent has the false TIF_SIGPENDING which
is cleared later by recalc_sigpending(). In this case it is correct to do
clear_tsk_thread_flag(p, TIF_SIGPENDING), but this almost never happens.

Oleg.

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