From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S933050AbcBPPrP (ORCPT <rfc822;w@1wt.eu>);
	Tue, 16 Feb 2016 10:47:15 -0500
Received: from mail-pa0-f42.google.com ([209.85.220.42]:35790 "EHLO
	mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932300AbcBPPrL (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 16 Feb 2016 10:47:11 -0500
Date: Wed, 17 Feb 2016 00:45:17 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.com>,
        Tejun Heo <tj@kernel.org>, Kyle McMartin <kyle@kernel.org>,
        Dave Jones <davej@codemonkey.org.uk>,
        Calvin Owens <calvinowens@fb.com>, linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH v4 2/3] printk: set may_schedule for some of
 console_trylock callers
Message-ID: <20160216154517.GB542@swordfish>
References: <1455302232-2252-1-git-send-email-sergey.senozhatsky@gmail.com>
 <1455302232-2252-3-git-send-email-sergey.senozhatsky@gmail.com>
 <20160216144306.GU12548@pathway.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160216144306.GU12548@pathway.suse.cz>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On (02/16/16 15:43), Petr Mladek wrote:
> On Sat 2016-02-13 03:37:11, Sergey Senozhatsky wrote:
> > console_unlock() allows to cond_resched() if its caller has
> > set `console_may_schedule' to 1, since
> > 'commit 8d91f8b15361 ("printk: do cond_resched() between lines while
> > outputting to consoles")'.
> > 
> > The rules are:
> > -- console_lock() always sets `console_may_schedule' to 1
> > -- console_trylock() always sets `console_may_schedule' to 0
> > 
> > However, console_trylock() callers (among them is printk()) do
> > not always call printk() from atomic contexts, and some of them
> > can cond_resched() in console_unlock(), so console_trylock()
> > can set `console_may_schedule' to 1 for such processes.
> > 
> > For !CONFIG_PREEMPT_COUNT kernels, however, console_trylock()
> > always sets `console_may_schedule' to 0.
> > 
> > It's possible to drop explicit preempt_disable()/preempt_enable()
> > in vprintk_emit(), because console_unlock() and console_trylock()
> > are now smart enough:
> > a) console_unlock() does not cond_resched() when it's unsafe
> >   (console_trylock() takes care of that)
> > b) console_unlock() does can_use_console() check.
> > 
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> 
> It looks safe after all.
> 
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> 

thanks.

	-ss