Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761558AbYHHVDu (ORCPT ); Fri, 8 Aug 2008 17:03:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759777AbYHHVD1 (ORCPT ); Fri, 8 Aug 2008 17:03:27 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38714 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758913AbYHHVD0 (ORCPT ); Fri, 8 Aug 2008 17:03:26 -0400 Date: Fri, 8 Aug 2008 13:57:26 -0700 (PDT) From: Linus Torvalds To: Andrew Morton cc: Peter Zijlstra , paulmck@linux.vnet.ibm.com, mingo@elte.hu, tglx@linutronix.de, marcin.slusarz@gmail.com, linux-kernel@vger.kernel.org, davem@davemloft.net, rostedt@goodmis.org Subject: Re: [PATCH] printk: robustify printk In-Reply-To: <20080808134657.fe439e56.akpm@linux-foundation.org> Message-ID: References: <1218202249.8625.106.camel@twins> <1218215454.8625.133.camel@twins> <1218217257.29098.2.camel@lappy.programming.kicks-ass.net> <1218219269.29098.5.camel@lappy.programming.kicks-ass.net> <20080808121428.646a8b3c.akpm@linux-foundation.org> <1218223269.29098.12.camel@lappy.programming.kicks-ass.net> <20080808123747.0db1c5dd.akpm@linux-foundation.org> <20080808203241.GH6760@linux.vnet.ibm.com> <1218227859.29098.24.camel@lappy.programming.kicks-ass.net> <20080808134657.fe439e56.akpm@linux-foundation.org> User-Agent: Alpine 1.10 (LFD 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1331 Lines: 34 On Fri, 8 Aug 2008, Andrew Morton wrote: > > Why are we fixing this, btw? The problem has been there forever and > people who hack the wakeup code could/should know about it anyway. All > they need to do is to disable klogd during development. Did the > problem recently become worse for some reason? It hasn't beemn there forever at all. Yes, there used to be reliance on the actual _scheduler_ locks. Doign a wake_up() would cause runqueue locks etc to be taken. But the xtime deadlock is fairly recent, and only happened with CFQ, I think. And _that_ is the irritating one. I personally wouldn't mind at all if there is some printk() dependency on the core runqueue rq->lock or on the RCU locking thing. But look at xtime_lock. THAT is a disaster. Just grep for it. So I personally actually like the RCU version best. Yes, it still depends on really core locking. But it's really core and low-level and _confined_ locking, where a comment in a single place would probably suffice. Compare that to all the places where we take the xtime_lock for writing! Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/