Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752002AbdI1QTA (ORCPT ); Thu, 28 Sep 2017 12:19:00 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:39715 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751345AbdI1QS7 (ORCPT ); Thu, 28 Sep 2017 12:18:59 -0400 Date: Thu, 28 Sep 2017 18:18:50 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: "Levin, Alexander (Sasha Levin)" , Sasha Levin , "linux-kernel@vger.kernel.org List" , Ingo Molnar , "jiangshanlai@gmail.com" , "dipankar@in.ibm.com" , Andrew Morton , Mathieu Desnoyers , Josh Triplett , Thomas Gleixner , Steven Rostedt , "dhowells@redhat.com" , Eric Dumazet , Fr?d?ric Weisbecker , Oleg Nesterov , "bobby.prani@gmail.com" Subject: Re: [PATCH v3 tip/core/rcu 40/40] rcu: Make non-preemptive schedule be Tasks RCU quiescent state Message-ID: <20170928161850.rud7fmiaxwhch6fu@hirez.programming.kicks-ass.net> References: <20170419165805.GB10874@linux.vnet.ibm.com> <1492621117-13939-40-git-send-email-paulmck@linux.vnet.ibm.com> <20170928123055.GI3521@linux.vnet.ibm.com> <20170928153813.7cernglt2d7umhpe@sasha-lappy> <20170928160514.GM3521@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170928160514.GM3521@linux.vnet.ibm.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1108 Lines: 23 On Thu, Sep 28, 2017 at 09:05:14AM -0700, Paul E. McKenney wrote: > > do_async_page_fault+0x72/0x90 arch/x86/kernel/kvm.c:271 > > async_page_fault+0x22/0x30 arch/x86/entry/entry_64.S:1069 > > RIP: 0010:format_decode+0x240/0x830 lib/vsprintf.c:1996 > > RSP: 0018:ffff88003b2df520 EFLAGS: 00010283 > > RAX: 000000000000003f RBX: ffffffffb5d1e141 RCX: ffff88003b2df670 > > RDX: 0000000000000001 RSI: dffffc0000000000 RDI: ffffffffb5d1e140 > > RBP: ffff88003b2df560 R08: dffffc0000000000 R09: 0000000000000000 > > R10: ffff88003b2df718 R11: 0000000000000000 R12: ffff88003b2df5d8 > > R13: 0000000000000064 R14: ffffffffb5d1e140 R15: 0000000000000000 > > vsnprintf+0x173/0x1700 lib/vsprintf.c:2136 > > We took a page fault in vsnprintf() while doing link_path_walk(), > which looks to be within an RCU read-side critical section. > > Maybe the page fault confused lockdep? > > Sigh. It is going to be a real pain if all printk()s need to be > outside of RCU read-side critical sections due to the possibility of > page faults... printk() _should_ not fault AFAIK. If it does, you've done something dodgy.