linux-kernel - Re: BUG in 2.6.20-rt8

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Message-Id: <20070224.223744.59470086.davem@davemloft.net>
Date:	Sat, 24 Feb 2007 22:37:44 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	mingo@...e.hu
Cc:	paulmck@...ux.vnet.ibm.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: BUG in 2.6.20-rt8

From: Ingo Molnar <mingo@...e.hu>
Date: Sun, 25 Feb 2007 07:27:47 +0100

> 
> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > I got the following running stock 2.6.20-rt8 on an 4-CPU 1.8GHz 
> > Opteron box.  The machine continued to run a few rounds of kernbench 
> > and LTP. Looks a bit scary -- a tasklet was "stolen" from 
> > __tasklet_action().
> > 
> > Thoughts?  In the meantime, kicking it off again to see if it repeats.
> 
> > BUG: at kernel/softirq.c:559 __tasklet_action()
> 
> this seems to happen very sporadically. Seems to happen more likely on 
> hyperthreading CPUs. It is very likely caused by the 
> redesign-tasklet-locking-to-be-sane patch below - which is a quick hack 
> of mine from early -rt days. Can you see any obvious bug in it? The 
> cmpxchg logic is certainly a bit ... tricky, locking-wise.

Ingo, please don't use cmpxchg() in generic code, we support several
processors that simply cannot do it.

Instead of saying "it's just something special in -rt for now", take
it out now so that what you do eventually push upstream does get
tested.

Thanks.
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