From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754037AbeDRO3z (ORCPT ); Wed, 18 Apr 2018 10:29:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:39288 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753975AbeDRO3s (ORCPT ); Wed, 18 Apr 2018 10:29:48 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 95824204EF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Wed, 18 Apr 2018 10:29:43 -0400 From: Steven Rostedt To: Sergey Senozhatsky Cc: Petr Mladek , Andrew Morton , Peter Zijlstra , Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] printk: wake up klogd in vprintk_emit Message-ID: <20180418102943.5aa0ffc4@gandalf.local.home> In-Reply-To: <20180414030145.26304-1-sergey.senozhatsky@gmail.com> References: <20180414030145.26304-1-sergey.senozhatsky@gmail.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 14 Apr 2018 12:01:45 +0900 Sergey Senozhatsky wrote: > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -1888,6 +1888,7 @@ asmlinkage int vprintk_emit(int facility, int level, > > printed_len = log_output(facility, level, lflags, dict, dictlen, text, text_len); > > + wake_up_klogd(); > logbuf_unlock_irqrestore(flags); You can't do this, because the scheduler can call printk_deferred() with the rq lock held, and printk_deferred() will grab the logbuf lock. Calling wake_up_klogd() will grab the rq lock and give us a A-B<->B-A locking order. -- Steve