[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <48A0F024.30609@novell.com>
Date: Mon, 11 Aug 2008 22:06:28 -0400
From: Gregory Haskins <ghaskins@...ell.com>
To: Steven Rostedt <rostedt@...dmis.org>
CC: David Miller <davem@...emloft.net>, a.p.zijlstra@...llo.nl,
jkacur@...il.com, linux-rt-users@...r.kernel.org,
linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de
Subject: Re: [PATCH] BUG: using smp_processor_id() in preemptible [00000000]
code: caller is __qdisc_run
Steven Rostedt wrote:
> On Mon, 11 Aug 2008, David Miller wrote:
>
>
>> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>> Date: Mon, 11 Aug 2008 23:09:38 +0200
>>
>>
>>> On Mon, 2008-08-11 at 14:00 -0700, David Miller wrote:
>>>
>>>> From: "John Kacur" <jkacur@...il.com>
>>>> Date: Mon, 11 Aug 2008 15:11:46 +0200
>>>>
>>>>
>>>>> __qdisc_run() calls qdisc_restart() which calls
>>>>> handle_dev_cpu_collision(skb, dev, q); and then the problem shows up
>>>>> here:
>>>>> __get_cpu_var(netdev_rx_stat).cpu_collision++;
>>>>>
>>>>> The solution is to disable interrupts around the above increment. Here
>>>>> is an attached patch to do so. (Thank's to Peter Zijlstra for help in
>>>>> the analysis and dropping the answer in my lap, so if I got it right
>>>>> it is due to his help, but if I messed it up, then I did that part all
>>>>> by myself.)
>>>>>
>>>> __qdisc_run() always runs in software interrupt context,
>>>> so I guess this is some problem with the -rt stuff running
>>>> software interrupts in threads?
>>>>
>>> Hmm, good point - and those threads should be cpu affine on -rt if I'm
>>> not mistaken. Steven, do you happen to remember details?
>>>
>> The key issue is whether those threads run software interrupts
>> in a compatible environment. And such a proper environment allows
>> plain smp_processor_id() without any special preparations.
>>
>>
>
> Yes, we have a softirq thread per CPU. We should have a test in the
> smp_processor_id for rt to not bug if it is called by known "per_cpu"
> threads.
>
something like
#ifdef CONFIG_PREEMPT_RT
WARN_ON(!in_atomic() && current->rt.nr_cpus_allowed > 1);
#else
WARN_ON(!in_atomic());
#endif
would probably work and be fairly efficient. Of course nr_cpus_allowed
technically could be adjusted at any time, so perhaps not. Its probably
good enough for a warning check, however.
> -- Steve
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
Download attachment "signature.asc" of type "application/pgp-signature" (258 bytes)
Powered by blists - more mailing lists