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 for Android: free password hash cracker in your pocket

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

Date:	Wed, 13 Aug 2014 10:12:15 +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 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.

Content of type "application/pgp-signature" skipped