Re: [PATCH] nommu: add page_align to mmap

[Bob Liu <lliubbo@gmail.com>]

On Thu, May 5, 2011 at 9:38 AM, Greg Ungerer <gerg@snapgear.com> wrote:
> On 05/05/11 07:13, Andrew Morton wrote:
>>
>> On Wed, 27 Apr 2011 15:12:14 +0800
>> Bob Liu<lliubbo@gmail.com>  wrote:
>>
>>> 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?  What 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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>