Re: 2 TB wraparound on snapshots on kernels < 2.6.33

[Phillip Susi <psusi@cfl.rr.com>]

Aha!  I looked at the code carefully as it aroused my suspicions, but I
couldn't quite work out how it actually caused the problem.  Good catch.

On 6/16/2010 9:45 AM, Mikulas Patocka wrote:
> The bug existed even in upstream, but only in 2.6.32 kernel. The reason 
> was this function:
> static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
>                                       sector_t sector)
> {
>         return (sector & ~store->chunk_mask) >> store->chunk_shift;
> }
> 
> "store->chunk_mask" was changed to be unsigned in 2.6.32, so it was 
> masking the sector with 32-bit value. In 2.6.33 that masking was removed. 
> Ubuntu picked that 2.6.32 patch but didn't pick further patches.
> 
> Mikulas