linux-kernel - Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle tasks

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]

Date:	Wed, 13 Aug 2014 15:40:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle
 tasks

On Wed, Aug 13, 2014 at 05:48:18AM -0700, Paul E. McKenney wrote:
> On Wed, Aug 13, 2014 at 10:12:15AM +0200, Peter Zijlstra wrote:
> > On Mon, Aug 11, 2014 at 03:49:04PM -0700, Paul E. McKenney wrote:
> > > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > > 
> > > Because idle-task code may need to be patched, RCU-tasks need to wait
> > > for idle tasks to schedule.  This commit therefore detects this case
> > > via context switch.  Block CPU hotplug during this time to avoid sending
> > > IPIs to offline CPUs.
> > > 
> > > Note that checking for changes in the dyntick-idle counters is tempting,
> > > but wrong.  The reason that it is wrong is that a interrupt or NMI can
> > > increment these counters without necessarily allowing the idle tasks to
> > > make any forward progress.
> > 
> > I'm going to NAK this.. with that rcu_idle patch I send there's
> > typically only a single idle function thats out of bounds and if its
> > more it can be made that with a bit of tlc to the cpuidle driver in
> > question.
> > 
> > This needs _FAR_ more justification than a maybe and a want.
> 
> Peter, your patch might be a good start, but I didn't see any reaction
> from Steven or Masami and it did only x86.

That's not an excuse for doing horrible things. And inventing new infra
that needs to wake all CPUs is horrible.

Content of type "application/pgp-signature" skipped