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

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Message-ID: <1329242378.3675.71.camel@mfleming-mobl1.ger.corp.intel.com>
Date:	Tue, 14 Feb 2012 17:59:38 +0000
From:	Matt Fleming <matt@...sole-pimps.org>
To:	David Howells <dhowells@...hat.com>
Cc:	linux-arch@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	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 Tue, 2012-02-14 at 15:56 +0000, 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.

->blocked can only ever be altered by current, not another thread. See
the following comment from sigprocmask() in kernel/signal.c,

       /* Lockless, only current can change ->blocked, never from irq */
        if (oldset)                                                                                      
                *oldset = tsk->blocked;                                                                  

-- 
Matt Fleming, Intel Open Source Technology Center

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