linux-kernel - Re: safety of *mutex_unlock() (Was: [BUG] signal: sighand unprotected when accessed by /proc)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140611172958.GF4581@linux.vnet.ibm.com>
Date:	Wed, 11 Jun 2014 10:29:58 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Clark Williams <williams@...hat.com>
Subject: Re: safety of *mutex_unlock() (Was: [BUG] signal: sighand
	unprotected when accessed by /proc)

On Wed, Jun 11, 2014 at 07:17:34PM +0200, Oleg Nesterov wrote:
> On 06/11, Oleg Nesterov wrote:
> >
> > On 06/11, Paul E. McKenney wrote:
> >
> > >  	raw_spin_unlock_irqrestore(&rnp->lock, flags);
> > >  	rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
> > >  	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
> > >
> > > +	/* Wait until boostee is done accessing mtx before reinitializing. */
> > > +	wait_for_completion(&rnp->boost_completion);
> > > +
> >
> > I must have missed something, I dont understand why we need ->boost_completion.
> >
> > What if you simply move that rt_mutex into rcu_node ?
> >
> > Or. Given that rcu_boost_kthread() never exits, it can declare this mutex
> > on stack and pass the pointer to rcu_boost() ?
> 
> Ah, please ignore, I forgot about init_proxy_locked(). Although perhaps this
> can be solved easily.

You beat me to it.  ;-)

I was thinking of ->boost_completion as the way to solve it easily, but
what did you have in mind?

							Thanx, Paul

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/