linux-kernel - Re: [PATCH] locking/osq: Drop the overload of osq lock

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: <20160625192958.GA30927@twins.programming.kicks-ass.net>
Date:	Sat, 25 Jun 2016 21:29:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	panxinhui <xinhui@...ux.vnet.ibm.com>
Cc:	Boqun Feng <boqun.feng@...il.com>,
	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...hat.com, dave@...olabs.net,
	will.deacon@....com, Waiman.Long@....com, benh@...nel.crashing.org
Subject: Re: [PATCH] locking/osq: Drop the overload of osq lock

On Sat, Jun 25, 2016 at 09:20:25PM +0200, Peter Zijlstra wrote:
> On Sun, Jun 26, 2016 at 01:27:56AM +0800, panxinhui wrote:
> > >> Would that not have issues where the owner cpu is kept running but the
> > >> spinner (ie. _this_ vcpu) gets preempted? I would think that in that
> > >> case we too want to stop spinning.
> > >> 
> > > 
> > do  you mean that the spinner detect itself had yield out during the
> > big spin loop?
> > 
> > It is very possible to happen.  BUT if spinner(on this vcpu) yield
> > out, the next spinner would break the spin loop.  AND if spinner
> > detect itself yield out once, it’s very possible to get the osq lock
> > soon as long as the ower vcpu is running.
> > 
> > SO I think we need just check the owner vcpu’s yield_count.
> 
> I had a quick look at KVM and it looks like it only has
> kvm_cpu::preempted, which would suggest the interface boqun proposed.

Xen seems to have vcpu_runstate_info::state where any !0 state means its
not running, so that too allows implementing that variant.