Re: [PATCH v2] nommu: add page_align to mmap

[Bob Liu <lliubbo@gmail.com>]

On Wed, Jun 8, 2011 at 6:19 PM, Greg Ungerer <gerg@snapgear.com> wrote:
>
> Hi Bob,
>
> On 08/06/11 17:18, Bob Liu wrote:
>>
>> Hi, Greg
>>
>> On Wed, Jun 8, 2011 at 12:47 PM, Greg Ungerer<gerg@snapgear.com>  wrote:
>>>
>>> Hi Bob,
>>>
>>> On 07/06/11 16:19, Bob Liu wrote:
>>>>
>>>> On Fri, Jun 3, 2011 at 2:37 PM, Greg Ungerer<gerg@snapgear.com>
>>>>  Ã¡wrote:
>>>>>
>>>>> Hi Bob,
>>>>>
>>>>> On 06/05/11 16:03, Bob Liu wrote:
>>>>>>
>>>>>> Currently on nommu arch mmap(),mremap() and munmap() doesn't do
>>>>>> page_align()
>>>>>> which isn't consist with mmu arch and cause some issues.
>>>>>>
>>>>>> First, some drivers' mmap() function depends on vma->vm_end -
>>>>>> vma->start
>>>>>> is
>>>>>> page aligned which is true on mmu arch but not on nommu. eg: uvc
>>>>>> camera
>>>>>> driver.
>>>>>>
>>>>>> Second munmap() may return -EINVAL[split file] error in cases when end
>>>>>> is
>>>>>> not
>>>>>> page aligned(passed into from userspace) but vma->vm_end is aligned
>>>>>> dure
>>>>>> to
>>>>>> split or driver's mmap() ops.
>>>>>>
>>>>>> This patch add page align to fix those issues.
>>>>>
>>>>> This is actually causing me problems on head at the moment.
>>>>> git bisected to this patch as the cause.
>>>>>
>>>>> When booting on a ColdFire (m68knommu) target the init process (or
>>>>> there abouts at least) fails. Last console messages are:
>>>>>
>>>>> á...
>>>>> áVFS: Mounted root (romfs filesystem) readonly on device 31:0.
>>>>> áFreeing unused kernel memory: 52k freed (0x401aa000 - 0x401b6000)
>>>>> áUnable to mmap process text, errno 22
>>>>>
>>>>
>>>> Oh, bad news. I will try to reproduce it on my board.
>>>> If you are free please enable debug in nommu.c and then we can see what
>>>> caused the problem.
>>>
>>> Yep, with debug on:
>>>
>>> á...
>>> áVFS: Mounted root (romfs filesystem) readonly on device 31:0.
>>> áFreeing unused kernel memory: 52k freed (0x4018c000 - 0x40198000)
>>> á==>  do_mmap_pgoff(,0,6780,5,1002,0)
>>> á<== do_mmap_pgoff() = -22
>>> áUnable to mmap process text, errno 22
>>>
>>
>> Since I can't reproduce this problem, could you please attach the
>> whole dmesg log with nommu debug on or
>> you can step into to see why errno 22 is returned, is it returned by
>> do_mmap_private()?
>
> There was no other debug messages with debug turned on in nommu.c.
> (I can give you the boot msgs before this if you want, but there
> was no nommu.c debug in it).
>
> But I did trace it into do_mmap_pgoff() to see what was failing.
> It fails based on the return value from:
>
>          addr = file->f_op->get_unmapped_area(file, addr, len,
>                                                      pgoff, flags);
>

Thanks for this information.
But it's a callback function. I still can't know what's the problem maybe.
Would you do me a favor to do more trace to see where it callback to,
fs or some driver etc..?

>
> Theres only one call of this inside do_mmap_pgoff() so you its
> easy to find.
>
> Regards
> Greg
>
>
>
>>> I can confirm that the PAGE_ALIGN(len) change in do_mmap_pgoff()
>>> is enough to cause this too.
>>>
>>> Regards
>>> Greg
>>>
>>>
>>>
>>>
>>>>> I haven't really debugged it any further yet. But that error message
>>>>> comes from fs/binfmt_flat.c, it is reporting a failed do_mmap() call.
>>>>>
>>>>> Reverting that this patch and no more problem.
>>>>>
>>>>> Regards
>>>>> Greg
>>>>>

-- 
Regards,
--Bob

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