Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752609AbdI1LNc (ORCPT ); Thu, 28 Sep 2017 07:13:32 -0400 Received: from mail-pg0-f67.google.com ([74.125.83.67]:36258 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750929AbdI1LNb (ORCPT ); Thu, 28 Sep 2017 07:13:31 -0400 X-Google-Smtp-Source: AOwi7QBmulpVRqjQNVUQneDAfsWb9CrE9t2qqqmvCy8MB0PpwV6mn5ermpU8I8Q/gsndObRciqxpqg== Date: Thu, 28 Sep 2017 20:13:26 +0900 From: Sergey Senozhatsky To: "Levin, Alexander (Sasha Levin)" Cc: Peter Zijlstra , Sasha Levin , Thomas Gleixner , Ingo Molnar , "linux-kernel@vger.kernel.org List" , "pmladek@suse.com" , "sergey.senozhatsky@gmail.com" , "rostedt@goodmis.org" Subject: Re: sched: serial port lockdep warning when offlining CPUs Message-ID: <20170928111325.GA30818@jagdpanzerIV.localdomain> References: <20170928093847.zgcgvxb7ajiaywbr@hirez.programming.kicks-ass.net> <20170928110428.ew5ukfihb3bdiszr@sasha-lappy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170928110428.ew5ukfihb3bdiszr@sasha-lappy> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1015 Lines: 30 On (09/28/17 11:04), Levin, Alexander (Sasha Levin) wrote: > On Thu, Sep 28, 2017 at 11:38:47AM +0200, Peter Zijlstra wrote: > >On Thu, Sep 28, 2017 at 02:19:46AM -0700, Sasha Levin wrote: > >> Hi all, > >> > >> I seem to be hitting the following warning when offlining CPUs on the > >> latest -next kernel: > >> > >> [289683102.607076] Unregister pv shared memory for cpu 8 > >> [289683102.622922] select_fallback_rq: 3 callbacks suppressed > > > >This is because you hit a printk() from the scheduler, that's known > >broken (along with the rest of printk). > > > >You forgot to actually include that printk() though I suspect it reads > >like: > > > > "process %d (%s) no longer affine to cpu%d\n" > > > >Now that uses printk_deferred() which _should_ work lots better, but > >clearly the printk() stuff went wobbly again. > > Hm, so is this an actual possible lockup, or just a false positive? a possible one. printk() used to lockdep_off()/lockdep_on() in "dangerous places" before, but not anymore. -ss