netdev - Re: 2.6.25rc7 lockdep trace

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Message-Id: <1206752049.22530.105.camel@johannes.berg>
Date:	Sat, 29 Mar 2008 01:54:09 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	David Miller <davem@...emloft.net>
Cc:	davej@...emonkey.org.uk, netdev@...r.kernel.org
Subject: Re: 2.6.25rc7 lockdep trace


> >  stack backtrace:
> >  Pid: 2308, comm: NetworkManager Not tainted 2.6.25-0.161.rc7.fc9.i686 #1
> >   [print_circular_bug_tail+91/102] print_circular_bug_tail+0x5b/0x66
> >   [print_circular_bug_entry+57/67] ? print_circular_bug_entry+0x39/0x43
> >   [__lock_acquire+2488/3089] __lock_acquire+0x9b8/0xc11
> >   [_spin_unlock_irq+34/47] ? _spin_unlock_irq+0x22/0x2f
> >   [lock_acquire+106/144] lock_acquire+0x6a/0x90
> >   [flush_workqueue+0/133] ? flush_workqueue+0x0/0x85
> >   [flush_workqueue+68/133] flush_workqueue+0x44/0x85
> >   [flush_workqueue+0/133] ? flush_workqueue+0x0/0x85
> >   [flush_scheduled_work+13/15] flush_scheduled_work+0xd/0xf
> >   [<d096d80a>] tulip_down+0x20/0x1a3 [tulip]
> >   [trace_hardirqs_on+233/266] ? trace_hardirqs_on+0xe9/0x10a
> >   [dev_deactivate+177/222] ? dev_deactivate+0xb1/0xde
> 
> Yes, see for example:
> 
> http://www.mail-archive.com/netdev@vger.kernel.org/msg31718.html
> 
> You can't flush a workqueue in the device close handler
> exactly because of this locking conflict.
> 
> Nobody has come up with a suitable way to fix this yet.

Maybe we should check which schedule_work users actually lock the rtnl
within the work function and move them to a uses-rtnl-in-work workqueue
so that everybody else can have rtnl around flush.

Depending on how many users there are that might not be feasible, but I
have so far only seen linkwatch_event() lock the rtnl within the work
function and everybody else seems to want to use the rtnl around the
flushing.

johannes

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