linux-kernel - Re: [PATCH 20/40] mn10300: Use set_current_blocked() and block

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Date:	Tue, 14 Feb 2012 19:24:27 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Matt Fleming <matt@...sole-pimps.org>, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Matt Fleming <matt.fleming@...el.com>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	Al Viro <viro@...iv.linux.org.uk>, linux-am33-list@...hat.com
Subject: Re: [PATCH 20/40] mn10300: Use set_current_blocked() and
	block_sigmask()

On 02/14, David Howells wrote:
>
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > No, only current can change ->blocked. This is even documented in
> > sigprocmask(). And more, the only correct way to change ->blocked
> > is set_current_blocked(). OK, with a couple of "I know what I am
> > doing" exceptions in kernel/signal.c.
>
> I was looking at force_sig_info() and derivatives.  Is that what you refer to?

Ah, sorry, forgot to mention...

force_sig_info() (and its callers) need the cleanups and fixes. It
is almost always wrong if t != current.

For example, please look at

	[PATCH 1/4] signal: give SEND_SIG_FORCED more power to beat SIGNAL_UNKILLABLE
	http://marc.info/?l=linux-kernel&m=132890442717122

Hopefully we can fix all ab-users soon.



Just in case... if we race with force_sig_info() the task will be
killed anyway. But I agree, this is not nice and should be fixed.
And in any case, there are other places which assume it is safe
to read current->blocked lockless.

> If so, is it worth providing a force_sig_info_current(),
> force_sigsegv_current() and force_sig_current() to make things clearer to grep
> for, I wonder?

Yes, I think the "task_struct *t" argument should die.

Oleg.

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