2.5.55-rmk1: user space lossage

[David Woodhouse]

 < Snip long thread about init segfaulting immediately at boot on 2.5.55 >

ch at murgatroid.com said:
> I just dropped jffs2 from 2.5.52 into 2.5.55 and it works, too.

ch at murgatroid.com said:
> Aha!  This is the problem: 
> -       .mmap =         generic_file_mmap,
> +       .mmap =         generic_file_readonly_mmap,
> If you reverese this change, 2.5.55-rmk1 behaves.

Er, yes. generic_file_readonly_mmap() silently removed the VM_MAYWRITE bit 
from vma->vm_flags when init made a _PRIVATE_ writable mapping, apparently 
on the basis that we have no writepage().

Then we return success anyway.

Then init segfaults when it touches something in that mapping.

/me blames akpm. :)

--
dwmw2