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

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Date:	Tue, 14 Feb 2012 18:23:40 +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:
>
> Matt Fleming <matt@...sole-pimps.org> wrote:
>
> >  asmlinkage long sys_sigsuspend(int history0, int history1, old_sigset_t mask)
> >  {
> > -	mask &= _BLOCKABLE;
> > -	spin_lock_irq(&current->sighand->siglock);
> > +	sigset_t blocked;
> > +
> >  	current->saved_sigmask = current->blocked;
>
> Can this line create a race, now that it's not protected by a lock?  It is
> possible for current->blocked to get altered by another thread.

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.

Oleg.

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