Philippe Gerum wrote:
> On Tue, 2009-06-30 at 11:26 +0200, Gilles Chanteperdrix wrote:
>> Philippe Gerum wrote:
>>> On Tue, 2009-06-30 at 11:21 +0200, Gilles Chanteperdrix wrote:
>>>> Philippe Gerum wrote:
>>>>> On Tue, 2009-06-30 at 10:42 +0200, Gilles Chanteperdrix wrote:
>>>>>> Jan Kiszka wrote:
>>>>>>> Jan Kiszka wrote:
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> seen such loops before? This particular trace is from a 2.6.29.3 kernel
>>>>>>>> with ipipe-2.3-01 (SMP/PREEMPT_VOLUNTARY), but the same happens with
>>>>>>>> 2.6.29.5/2.3-03:
>>>>>>>>
>>>>>>>> :| +func -653 0.084 __ipipe_handle_exception+0x11
>>>>>>>> (page_fault+0x26)
>>>>>>>> :| +func -653 0.096 ipipe_check_context+0xd
>>>>>>>> (__ipipe_handle_exception+0x71)
>>>>>>>> :| #end 0x80000000 -653 0.069 do_page_fault+0x33
>>>>>>>> (__ipipe_handle_exception+0x1ff)
>>>>>>>> : #func -653 0.078 __ipipe_unstall_root+0x9
>>>>>>>> (do_page_fault+0x3cb)
>>>>>>>> :| #begin 0x80000000 -653 0.068 __ipipe_unstall_root+0x34
>>>>>>>> (do_page_fault+0x3cb)
>>>>>>>> :| +end 0x80000000 -653 0.069 __ipipe_unstall_root+0x59
>>>>>>>> (do_page_fault+0x3cb)
>>>>>>>> : +func -653 0.060 down_read_trylock+0x4
>>>>>>>> (do_page_fault+0x424)
>>>>>>>> : +func -653 0.068 _spin_lock_irqsave+0x9
>>>>>>>> (__down_read_trylock+0x16)
>>>>>>>> : +func -653 0.108 ipipe_check_context+0xd
>>>>>>>> (_spin_lock_irqsave+0x1d)
>>>>>>>> : #func -652 0.066 _spin_unlock_irqrestore+0x4
>>>>>>>> (__down_read_trylock+0x3f)
>>>>>>>> : #func -652 0.069 __ipipe_restore_root+0x4
>>>>>>>> (_spin_unlock_irqrestore+0x21)
>>>>>>>> : #func -652 0.074 __ipipe_unstall_root+0x9
>>>>>>>> (__ipipe_restore_root+0x2c)
>>>>>>>> :| #begin 0x80000000 -652 0.066 __ipipe_unstall_root+0x34
>>>>>>>> (__ipipe_restore_root+0x2c)
>>>>>>>> :| +end 0x80000000 -652 0.069 __ipipe_unstall_root+0x59
>>>>>>>> (__ipipe_restore_root+0x2c)
>>>>>>>> : +func -652 0.096 find_vma+0x4
>>>>>>>> (do_page_fault+0x465)
>>>>>>>> : +func -652 0.150 ltt_run_filter_default+0x4
>>>>>>>> (_ltt_specialized_trace+0xc1)
>>>>>>>> : +func -652 0.098 handle_mm_fault+0x11
>>>>>>>> (do_page_fault+0x537)
>>>>>>>> : +func -652 0.090 _spin_lock+0x4
>>>>>>>> (handle_mm_fault+0x680)
>>>>>>>> : +func -652 0.063 ptep_set_access_flags+0x9
>>>>>>>> (handle_mm_fault+0x6d1)
>>>>>>>> : +func -652 0.282 flush_tlb_page+0xd
>>>>>>>> (handle_mm_fault+0x6e7)
>>>>>>>> : +func -651 0.162 ltt_run_filter_default+0x4
>>>>>>>> (_ltt_specialized_trace+0xc1)
>>>>>>>> : +func -651 0.062 up_read+0x4
>>>>>>>> (do_page_fault+0x5a9)
>>>>>>>> : +func -651 0.072 _spin_lock_irqsave+0x9
>>>>>>>> (__up_read+0x1c)
>>>>>>>> : +func -651 0.117 ipipe_check_context+0xd
>>>>>>>> (_spin_lock_irqsave+0x1d)
>>>>>>>> : #func -651 0.074 _spin_unlock_irqrestore+0x4
>>>>>>>> (__up_read+0x92)
>>>>>>>> : #func -651 0.069 __ipipe_restore_root+0x4
>>>>>>>> (_spin_unlock_irqrestore+0x21)
>>>>>>>> : #func -651 0.060 __ipipe_unstall_root+0x9
>>>>>>>> (__ipipe_restore_root+0x2c)
>>>>>>>> :| #begin 0x80000000 -651 0.056 __ipipe_unstall_root+0x34
>>>>>>>> (__ipipe_restore_root+0x2c)
>>>>>>>> :| +end 0x80000000 -651 0.420 __ipipe_unstall_root+0x59
>>>>>>>> (__ipipe_restore_root+0x2c)
>>>>>>>> :| +func -650 0.084 __ipipe_handle_exception+0x11
>>>>>>>> (page_fault+0x26)
>>>>>>>>
>>>>>>>> and again and again...
>>>>>>>>
>>>>>>>> We are looping over a minor fault here (according to /proc/PID/stat),
>>>>>>>> the context is a Xenomai task in secondary mode. As the task no longer
>>>>>>>> processes signals in this state, the whole system is more or less
>>>>>>>> broken. Tomorrow I will try to find out the faulting address with an
>>>>>>>> instrumented kernel, but maybe you already have some ideas.
>>>>>>> The fault is apparently triggered by __xn_put_user(XNRELAX,
>>>>>>> thread->u_mode) in xnshadow_relax. thread->u_mode is pointing to an
>>>>>>> invalid region ATM. The questions are now: Who corrupted this, user
>>>>>>> space on init (not that likely) or kernel space later on (unpleasant
>>>>>>> thought)? Moreover: Why can't we recover from a fault on u_mode?
>>>>>> I already investigated such an issue, and my conclusion was that there
>>>>>> are some places in the code where we can not cope with a fault.
>>>>>> xnshadow_relax being such a place, because, if relax faults, then what
>>>>>> will the fault handler do? Call relax again. Fortunately, mlockall and
>>>>>> the nocow stuff fixes this.
>>>>> xnshadow_relax() faulting before the current thread bears the XNRELAX
>>>>> bit would mean that a creepy issue involving ondemand PTEs in _kernel_
>>>>> space must have caused this. Having the init_mm mappings known from all
>>>>> processes seems more relevant to this issue than anything nocow and/or
>>>>> mlockall could ever do to fix it.
>>>> u_mode is a user-space address.
>>>>
>>> Why do you think xnshadow_relax() would be called for an already relaxed
>>> thread?
>> Because the fault happens before it has finished relaxing ?
>>
>
> Well, no. Have a second look at the code.
Ok, you are right then, in my case the faults were probably due to vmalloc.
--
Gilles
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