On Thu, May 5, 2011 at 9:38 AM, Greg Ungerer <gerg@xxxxxxxxxxxx> wrote:
> On 05/05/11 07:13, Andrew Morton wrote:
>>
>> On Wed, 27 Apr 2011 15:12:14 +0800
>> Bob Liu<lliubbo@xxxxxxxxx> Âwrote:
>>
>>> Currently on nommu arch mmap(),mremap() and munmap() doesn't do
>>> page_align()
>>> which is incorrect and not consist with mmu arch.
>>> This patch fix it.
>>>
>>
>> Can you explain this fully please? ÂWhat was the user-observeable
>> behaviour before the patch, and after?
>>
>> And some input from nommu maintainers would be nice.
>
> Its not obvious to me that there is a problem here. Are there
> any issues caused by the current behavior that this fixes?
>
Yes, there is a issue.
Some drivers' mmap() function depend on (vma->vm_end - vma->start) is
page aligned which is true on mmu arch but not on nommu.
eg: uvc camera driver.
What's more, sometimes I got munmap() error.
The reason is split file: mm/nommu.c
do {
1614 if (start > vma->vm_start) {
1615 kleave(" = -EINVAL [miss]");
1616 return -EINVAL;
1617 }
1618 if (end == vma->vm_end)
1619 goto erase_whole_vma;
<<=====================here
1620 rb = rb_next(&vma->vm_rb);
1621 vma = rb_entry(rb, struct vm_area_struct, vm_rb);
1622 } while (rb);
1623 kleave(" = -EINVAL [split file]");
Because end is not page aligned (passed into from userspace) while
some unknown reason
vma->vm_end is aligned, this loop will fail and -EINVAL[split file]
error returned.
But it's hard to reproduce.
And in my opinion consist with mmu alway a better choice.
Thanks for your review.
--
Regards,
--Bob
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