netdev - Re: Linux 3.0 release

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Message-ID: <20110722212629.GA10833@electric-eye.fr.zoreil.com>
Date:	Fri, 22 Jul 2011 23:26:29 +0200
From:	Francois Romieu <romieu@...zoreil.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Ben Greear <greearb@...delatech.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David <david@...olicited.net>, Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: Linux 3.0 release

Stephen Hemminger <shemminger@...tta.com> :
> This a regression which probably began with
> 
> commit e22bee782b3b00bd4534ae9b1c5fb2e8e6573c5c
> Author: Tejun Heo <tj@...nel.org>
> Date:   Tue Jun 29 10:07:14 2010 +0200
> 
>     workqueue: implement concurrency managed dynamic worker pool
> 
> Before that it was perfectly legal for link watch code to
> call schedule_delayed_work from IRQ. This should be allowable;
> the code to manage the worker pool should handle it.

I beg to differ: see Ben's first report
(http://lists.openwall.net/netdev/2011/05/04/183).
                                       ^^

One of the code path in the netif_carrier code leads it to try and disable
a late workqueue to reenable it immediately (mod_workqueue anyone ?):
netif_carrier_on
-> linkwatch_fire_event
   -> linkwatch_schedule_work
      -> cancel_delayed_work
         -> del_timer_sync

The del_timer_sync has been here for ages. Afaiks it is not a new pool code
nor a schedule_delayed_work only problem.

-- 
Ueimor
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