Re: [PATCH 00/15] bitops: Change bitmap index from int to unsigned long

[Peter Zijlstra <peterz@infradead.org>]

On Tue, 2009-02-24 at 20:41 -0800, Justin Chen wrote:
> his patch is to change the bitmap index in the bitops from "int" to
> "unsigned long".
> 
> In many bitops implementations, the bitmap index is a signed int.  If
> the caller passes a large unsigned integer and we interpret it as
> being negative, we compute an address outside the bitmap.  This can
> cause memory corruption or other errors.
> 
> The issue that triggered me to do this change is the routine
> mark_bootmem_node() while we ran on an ia64 box with large memory.  As
> long as the EFI maps the available memory chunk at the physical
> address 0x200000000000 (or above), the routine mark_bootmem_node()
> will get the start PFN>=0x80000000.  While it calls the __free() with
> this sidx=0x80000000 (bit31 set), the bitops (test_and_clear_bit) will
> treat this idx as a negative number since it accepts it as an "int".
> It turns out the memory outside the bitmap will be corrupted.
> 
> Following 15 patches will change all the bitmap index "nr" in all
> bitops from "int" to "unsigned long".
> 
> The patch is based on 2.6.29-rc6
> 
> Please comment -

unsigned int wasn't large enough?