On 12/1/20 9:07 AM, Mike Snitzer wrote:

commit 22ada802ede8 ("block: use lcm_not_zero() when stacking
chunk_sectors") broke chunk_sectors limit stacking. chunk_sectors must
reflect the most limited of all devices in the IO stack.

Otherwise malformed IO may result. E.g.: prior to this fix,
->chunk_sectors = lcm_not_zero(8, 128) would result in
blk_max_size_offset() splitting IO at 128 sectors rather than the
required more restrictive 8 sectors.

And since commit 07d098e6bbad ("block: allow 'chunk_sectors' to be
non-power-of-2") care must be taken to properly stack chunk_sectors to
be compatible with the possibility that a non-power-of-2 chunk_sectors
may be stacked. This is why gcd() is used instead of reverting back
to using min_not_zero().

Applied for 5.10, thanks.

-- 
Jens Axboe