Gilles Chanteperdrix wrote:
> On Nov 13, 2007 6:10 PM, Philippe Gerum <[EMAIL PROTECTED]> wrote:
>> Gilles Chanteperdrix wrote:
>>> On Nov 13, 2007 3:17 PM, Jan Kiszka <[EMAIL PROTECTED]> wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> Hi,
>>>>>
>>>>> I am chasing a slab corruption bug which happens on a Xenomai+RTnet
>>>>> enabled box under heavy non real-time network load (which passes
>>>>> through rtnet and rtmac_vnic to Linux which does NAT and resend it to
>>>>> another rtmac_vnic). When reading some I-pipe tracer traces, I
>>>>> remarked that I forgot to replace a local_irq_save/local_irq_restore
>>>>> with local_irq_save_hw/local_irq_restore_hw in a real-time interrupt
>>>>> handler. I fixed this bug, and the slab corruption seems to be gone.
>>>> Hope you mean rtdm_lock_irqsave/irqrestore instead. Otherwise Xenomai's
>>>> domain state would not be updated appropriately - which is at least 
>>>> unclean.
>>> It is some low level secondary timer handling code, there is no rtdm
>>> involved. The code protected by the interrupt masking routines is one
>>> or two inline assembly instructions.
>>>
>>>> BTW, CONFIG_IPIPE_DEBUG_CONTEXT should have caught this bug as well.
>>> I am using an old I-pipe pacth without CONFIG_IPIPE_DEBUG_CONTEXT.
>>> I-pipe patch and Xenomai update is scheduled for when RT applications
>>> and drivers porting will be finished.
>>>
>>> Besides the BUG_ON(!ipipe_root_domain_p) in ipipe_restore_root and
>>> ipipe_unstall_root are unconditional.
>>>
>> What bothers me, is that even looking at the old 1.3 series here and on,
>> the code should exhibit a call chain like
>> local_irq_restore -> raw_local_irq_restore() -> __ipipe_restore_root ->
>> __ipipe_unstall_root -> __ipipe_sync_stage, without touching the current
>> domain pointer, which is ok, since well, it has to be right in the first
>> place. If we were running over a real-time handler, then I assume the
>> Xenomai domain was active. So BUG_ON() should have triggered if present
>> in __ipipe_unstall_root.
> 
> I am using an I-pipe arm 1.5-04 (now that I have done cat
> /proc/ipipe/version, I really feel ashamed). And it has no BUG_ON in
> __ipipe_unstall_root or __ipipe_restore_root. I promise, one day, I
> will switch to Xenomai 2.4.
> 
>> Additionally, calling __ipipe_sync_pipeline() would sync the current
>> stage, i.e. Xenomai, and run the real-time ISRs, not the Linux handlers.
>>
>> Mm, ok, in short: I have no clue.
> 
> The system runs stably, so I have to assume that calling
> local_irq_restore in a real-time interrupt handler can cause slab
> corruption. Strange.
> 

I guess this is likely not on your critical path, but when time allows,
I'd be interested to know whether such bug still occurs when using a
purely kernel-only tasking, assuming that you currently see this bug
with userland tasks. Basically, I wonder if migrating shadows between
both domains would not reveal the bug, since your real-time handler
starts being preemptible by hw IRQs as soon as it returns from
__ipipe_unstall_root, which forces local_irq_enable_hw().

-- 
Philippe.

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