Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751317AbcK2RLF (ORCPT ); Tue, 29 Nov 2016 12:11:05 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:52531 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755545AbcK2RKn (ORCPT ); Tue, 29 Nov 2016 12:10:43 -0500 Date: Tue, 29 Nov 2016 18:10:38 +0100 From: Peter Zijlstra To: Petr Mladek Cc: "Paul E. McKenney" , Josh Poimboeuf , Vince Weaver , "linux-kernel@vger.kernel.org" , Ingo Molnar , Arnaldo Carvalho de Melo , "dvyukov@google.com" Subject: Re: perf: fuzzer BUG: KASAN: stack-out-of-bounds in __unwind_start Message-ID: <20161129171038.GN3092@twins.programming.kicks-ass.net> References: <20161128215411.fkis7bbimjy4v4j7@treble> <20161129004021.GL3924@linux.vnet.ibm.com> <20161129055241.6dy2dt4q4ptazk2s@treble> <20161129124323.GJ3092@twins.programming.kicks-ass.net> <20161129151004.GU3924@linux.vnet.ibm.com> <20161129162920.GF21230@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161129162920.GF21230@pathway.suse.cz> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1290 Lines: 30 On Tue, Nov 29, 2016 at 05:29:20PM +0100, Petr Mladek wrote: > > > People are very busy polishing the turd we call printk, but from where > > > I'm sitting its terminally and unfixably broken. > > I still hope that we could do better :-) How? The console drivers are a complete trainwreck, you simply cannot build anything sensible ontop of a trainwreck. And from what I understood from talking to someone (I again forgot who) at LPC, the whole reason people were poking at this is that the block layer (or something thereabouts) prints a gazillion lines of crap when you attach a stupid amount of devices (through FC or other SAN like things). The way we've 'fixed' that in the scheduler (a fairly long time ago) when SGI complained about our printks taking too long (because they had 4096 CPUs), is to simply remove the printks (they're now hidden behind the sched_debug boot param). In any case, as long as printk has a globally serialized 'log', it, per design, will be worse than the console drivers its build upon. And them being shit precludes the entire stack from being useful. It mostly works, most of the time, and that seems to be what Linus wants, since its really the best we can have given the constraints. But for debugging, when you have a UART, it totally blows.