From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 4/5] watchdog: control hard lockup detection default Date: Mon, 18 Aug 2014 20:07:35 +0200 Message-ID: <20140818180735.GB4540@gmail.com> References: <1407768567-171794-1-git-send-email-dzickus@redhat.com> <1407768567-171794-5-git-send-email-dzickus@redhat.com> <20140818091644.GE25495@gmail.com> <20140818151737.GT49576@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: akpm@linux-foundation.org, kvm@vger.kernel.org, pbonzini@redhat.com, mingo@redhat.com, LKML , Ulrich Obergfell , Andrew Jones To: Don Zickus Return-path: Content-Disposition: inline In-Reply-To: <20140818151737.GT49576@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org * Don Zickus wrote: > On Mon, Aug 18, 2014 at 11:16:44AM +0200, Ingo Molnar wrote: > > > > * Don Zickus wrote: > > > > > The running kernel still has the ability to enable/disable at any > > > time with /proc/sys/kernel/nmi_watchdog us usual. However even > > > when the default has been overridden /proc/sys/kernel/nmi_watchdog > > > will initially show '1'. To truly turn it on one must disable/enable > > > it, i.e. > > > echo 0 > /proc/sys/kernel/nmi_watchdog > > > echo 1 > /proc/sys/kernel/nmi_watchdog > > > > This looks like a bug, why is this so? > > It is, but it always has been there in the case of the PMU > not being able to provide a resource for the hardlockup. > This change just exposes it more. There seems to be two issues: 1) When it's impossible to enable the hardlockup detector, it should default to -1 or so, and attempts to set it should return a -EINVAL or so. Bootup messages should also indicate when it's not possible to enable it but a user requests it. 2) The softlockup and hardlockup detection control variables should be in separate flags, inside and outside the kernel - they (should) not relate to each other. Thanks, Ingo