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 S1751989AbbJBVFQ (ORCPT <rfc822;w@1wt.eu>);
	Fri, 2 Oct 2015 17:05:16 -0400
Received: from www.linutronix.de ([62.245.132.108]:43437 "EHLO
	Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751340AbbJBVFN (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 2 Oct 2015 17:05:13 -0400
Date: Fri, 2 Oct 2015 23:04:29 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Eric Dumazet <eric.dumazet@gmail.com>
cc: Eric Dumazet <edumazet@google.com>,
        =?ISO-8859-15?Q?Holger_Hoffst=E4tte?= 
	<holger.hoffstaette@googlemail.com>,
        "David S. Miller" <davem@davemloft.net>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Stephen Hemminger <stephen@networkplumber.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>, stable@vger.kernel.org,
        netdev <netdev@vger.kernel.org>
Subject: Re: Soft lockup issue in Linux 4.1.9
In-Reply-To: <1443819583.32531.55.camel@edumazet-glaptop2.roam.corp.google.com>
Message-ID: <alpine.DEB.2.11.1510022302430.4500@nanos>
References: <1443650383.13282.10.camel@daevel.fr>  <560D1223.3070606@googlemail.com>  <CANn89i+B5T4Rhs8HnrC0+f+GhLvBFfpr4BVDvhkVOveSfy9B8Q@mail.gmail.com>  <560D1C5A.3050508@googlemail.com>  <CANn89iKvTUKZTiWQYbjXLr4NvYKDgd_mKYVzZHiSqk0e0OfGxA@mail.gmail.com>
  <alpine.DEB.2.11.1510022200130.4500@nanos> <1443819583.32531.55.camel@edumazet-glaptop2.roam.corp.google.com>
User-Agent: Alpine 2.11 (DEB 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, 2 Oct 2015, Eric Dumazet wrote:
> On Fri, 2015-10-02 at 22:04 +0200, Thomas Gleixner wrote:
> 
> > What makes sure, that the timer cannot be readded while that timer
> > callback is running?
> 
> What is exactly your question ?

CPU0   	  	       		CPU1

timer expires
  callback
				add timer
  timer_pending() == true
  ===> del_timer_sync()

I was just curious how this is prevented as I got lost in the
networking code as usual :)

Thanks,

	tglx