From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chai Wen Subject: Re: [PATCH 2/5] softlockup: make detector be aware of task switch of processes hogging cpu Date: Tue, 19 Aug 2014 09:36:05 +0800 Message-ID: <53F2AA05.1020509@cn.fujitsu.com> References: <1407768567-171794-1-git-send-email-dzickus@redhat.com> <1407768567-171794-3-git-send-email-dzickus@redhat.com> <20140818090319.GA25495@gmail.com> <20140818150658.GQ49576@redhat.com> <20140818180158.GA4540@gmail.com> <20140818184339.GB49576@redhat.com> <20140818190200.GB5074@gmail.com> <20140818203801.GE49576@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: Ingo Molnar , , , , , LKML To: Don Zickus Return-path: In-Reply-To: <20140818203801.GE49576@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 08/19/2014 04:38 AM, Don Zickus wrote: > On Mon, Aug 18, 2014 at 09:02:00PM +0200, Ingo Molnar wrote: >> >> * Don Zickus wrote: >> >>>>>> So I agree with the motivation of this improvement, but >>>>>> is this implementation namespace-safe? >>>>> >>>>> What namespace are you worried about colliding with? I >>>>> thought softlockup_ would provide the safety?? Maybe I >>>>> am missing something obvious. :-( >>>> >>>> I meant PID namespaces - a PID in itself isn't guaranteed >>>> to be unique across the system. >>> >>> Ah, I don't think we thought about that. Is there a better >>> way to do this? Is there a domain id or something that can >>> be OR'd with the pid? >> >> What is always unique is the task pointer itself. We use pids >> when we interface with user-space - but we don't really do that >> here, right? > > No, I don't believe so. Ok, so saving 'current' and comparing that should > be enough, correct? > I am not sure of the safety about using pid here with namespace. But as to the pointer of process, is there a chance that we got a 'historical' address saved in the 'softlockup_warn_pid(or address)_saved' and the current hogging process happened to get the same task pointer address? If it never happens, I think the comparing of address is ok. thanks chai wen > Cheers, > Don > . > -- Regards Chai Wen