From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760392AbcAKV7x (ORCPT ); Mon, 11 Jan 2016 16:59:53 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:49995 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760278AbcAKV7w (ORCPT ); Mon, 11 Jan 2016 16:59:52 -0500 Date: Mon, 11 Jan 2016 13:59:51 -0800 From: Andrew Morton To: Tejun Heo Cc: lkp@01.org, LKML , Kyle McMartin , Dave Jones , Jan Kara , Calvin Owens , Stephen Rothwell , kernel test robot , kernel-team@fb.com, Sergey Senozhatsky Subject: Re: [PATCH] printk: clear console_may_schedule on panic flushing Message-Id: <20160111135951.b5f81c02c6d2054164f618af@linux-foundation.org> In-Reply-To: <20160111184348.GF1898@mtj.duckdns.org> References: <878u3w95ke.fsf@yhuang-dev.intel.com> <20160111184348.GF1898@mtj.duckdns.org> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; 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 Mon, 11 Jan 2016 13:43:48 -0500 Tejun Heo wrote: > Commit "printk: do cond_resched() between lines while outputting to > consoles" made console flushing perform cond_resched() after each line > if the context allows as determined by whether the console lock was > acquired with console_lock(). The condition is carried in > console_may_schedule. > > During panic, console lock status is ignored and the messages are > forcifully flushed which is implemented by performing > console_trylock(); console_unlock(); sequence ignoring whether trylock > succeeds or fails. This means that the emergency flushing, after > trylock failure, may enter flushing path with console_may_schedule set > from the actual holder. > > As a system may panic from any context, this can lead to > cond_resched() being invoked from a non-sleepable context triggering > an extra warning dump while panicking which is noisy and can be > confusing. Besides, even when panicking from a sleepable context, we > don't want to be yielding during emergency message dumping. > > Currently, the emergency dumping is opencoded in panic(). This patch > replaces the open coded implementation with a new function, > console_flush_on_panic() and makes it explicitly clear > console_may_schedule before starting the emergency flushing. > Got that, thanks. Because the patch has significant information content I'd normally make it a standalone thing, but as it's destined for -stable I think I'll scrunch it into printk-do-cond_resched-between-lines-while-outputting-to-consoles.patch and merge the changelogs. You didn't comment on Sergey's observations (https://lkml.org/lkml/2015/12/2/1192), but I'm believing this is a separate issue and that this patch is still good.