linux-kernel - Re: Seeing "huh, entered softirq 8 ffffffff802682aa preempt_count 00000100, exited with 00010100?" in tip.git

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Date:	Thu, 29 Jan 2009 17:44:43 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	paulmck@...ux.vnet.ibm.com
CC:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Seeing "huh, entered softirq 8 ffffffff802682aa preempt_count
 00000100, exited with 00010100?" in tip.git

Paul E. McKenney wrote:
> On Thu, Jan 29, 2009 at 02:12:31PM -0800, Jeremy Fitzhardinge wrote:
>   
>> When I boot my x86-64 tip.git kernel under Xen, I'm seeing:
>>
>> pnp: PnP ACPI: disabled
>> NET: Registered protocol family 2
>> huh, entered softirq 8 ffffffff802682aa preempt_count 00000100, exited with 
>> 00010100?
>> IP route cache hash table entries: 512 (order: 0, 4096 bytes)
>> TCP established hash table entries: 1024 (order: 2, 16384 bytes)
>> [...]
>> XENBUS: Device with no driver: device/console/0
>> Freeing unused kernel memory: 372k freed
>> Red Hat nash version 6.0.19 starting
>> Mounting proc filesystem
>> Mounting sysfs filesystem
>> Creating /dev
>> BUG: scheduling while atomic: swapper/0/0x00010000
>> Modules linked in:
>> Pid: 0, comm: swapper Not tainted 2.6.29-rc3-tip #481
>> Call Trace:
>> [<ffffffff80238c1f>] __schedule_bug+0x62/0x66
>> [<ffffffff80211d2d>] ? retint_restore_args+0x5/0x20
>> [<ffffffff80503921>] __schedule+0x95/0x792
>> [<ffffffff802093aa>] ? _stext+0x3aa/0x1000
>> [<ffffffff802093aa>] ? _stext+0x3aa/0x1000
>> [<ffffffff805040c2>] schedule+0xe/0x22
>> [<ffffffff8020ff04>] cpu_idle+0x70/0x72
>> [<ffffffff804fc3a0>] cpu_bringup_and_idle+0x13/0x15
>> Creating initial device nodes
>> Setting up hotplug.
>>
>>
>> From what I can see, softirq 8 is the RCU softirq.  I don't know if the 
>> "scheduling while atomic" is related or not, but its two new schedulerish 
>> symptoms appearing at once, so I think its likely they're related.
>>     
>
> Hmmm...  Mysterious, as you seem to be using classic RCU, which hasn't
> changed in awhile.  Which branch of the tip tree are you using?
>   

tip/master.  It looks like this appeared since -rc1.  Mu current 
suspicion is the percpu changes, since I'm seeing some other strange 
symptoms.

    J
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