From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751235AbXAIJdW (ORCPT ); Tue, 9 Jan 2007 04:33:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751232AbXAIJdW (ORCPT ); Tue, 9 Jan 2007 04:33:22 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:57941 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751230AbXAIJdV (ORCPT ); Tue, 9 Jan 2007 04:33:21 -0500 Date: Tue, 9 Jan 2007 15:03:02 +0530 From: Srivatsa Vaddagiri To: Andrew Morton Cc: Oleg Nesterov , David Howells , Christoph Hellwig , Ingo Molnar , Linus Torvalds , linux-kernel@vger.kernel.org, Gautham shenoy Subject: Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist Message-ID: <20070109093302.GE589@in.ibm.com> Reply-To: vatsa@in.ibm.com References: <20070106154506.GC24274@in.ibm.com> <20070106163035.GA2948@tv-sign.ru> <20070106163851.GA13579@in.ibm.com> <20070106111117.54bb2307.akpm@osdl.org> <20070107110013.GD13579@in.ibm.com> <20070107115957.6080aa08.akpm@osdl.org> <20070107210139.GA2332@tv-sign.ru> <20070108155428.d76f3b73.akpm@osdl.org> <20070109050417.GC589@in.ibm.com> <20070108212656.ca77a3ba.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070108212656.ca77a3ba.akpm@osdl.org> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 08, 2007 at 09:26:56PM -0800, Andrew Morton wrote: > That's not correct. freeze_processes() will freeze *all* processes. I am not arguing whether all processes will be frozen. However my question was on the freeze point. Let me ask the question with an example: rtasd thread (arch/powerpc/platforms/pseries/rtasd.c) executes this simple loop: static int rtasd(void *unused) { i = first_cpu(cpu_online_map); while (1) { set_cpus_allowed(current, cpumask_of_cpu(i)); /* can block */ /* we should now be running on cpu i */ do_something_on_a_cpu(i); /* sleep for some time */ i = next_cpu(cpu, cpu_online_map); } } This thread makes absolutely -no- calls to try_to_freeze() in its lifetime. 1. Does this mean that the thread can't be frozen? (lets say that the thread's PF_NOFREEZE is not set) AFAICS it can still be frozen by sending it a signal and have the signal delivery code call try_to_freeze() .. 2. If the thread can be frozen at any arbitrary point of its execution, then I dont see what prevents cpu_online_map from changing under the feet of rtasd thread, In other words, we would have failed to provide the ability to *block* hotplug operations from happening concurrently. > All of them are forced to enter refrigerator(). ^^^^^^ *forced*, yes ..that's the point of concern .. Warm regards, vatsa