linux-kernel - Re: [PATCH tip/core/rcu 03/15] rcu: Properly initialize ->boost

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: <20120906205856.GA2448@linux.vnet.ibm.com>
Date:	Thu, 6 Sep 2012 13:58:56 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 03/15] rcu: Properly initialize
 ->boost_tasks on CPU offline

On Thu, Sep 06, 2012 at 04:40:38PM +0200, Peter Zijlstra wrote:
> On Thu, 2012-08-30 at 11:56 -0700, Paul E. McKenney wrote:
> > When rcu_preempt_offline_tasks() clears tasks from a leaf rcu_node
> > structure, it does not NULL out the structure's ->boost_tasks field.
> > This commit therefore fixes this issue. 
> 
> What would have been the side-effects of this? Would rcu-boosting have
> been able to go funny on hotplug, and if so, how?

In some circumstances, this could prevent any future RCU boosting.
The ->boost_tasks field would be non-NULL, so it wouldn't ever try
boosting again, having been fooled into thinking that the previous
boost attempt was still in progress.

The expected segfault is prevented by the fact that an attempt to
initiate a boost first checks for ->boost_tasks being non-NULL,
and if so, declines to wake up the RCU-boost kthread.

							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/