On 2020-08-06 14:58, Keith Busch wrote:
> A previous commit aligning splits to physical block sizes inadvertently
> modified one return case such that that it now returns 0 length splits
> when the number of sectors doesn't exceed the physical offset. This
> later hits a BUG in bio_split(). Restore the previous working behavior.
>
> Reported-by: Eric Deal <eric.deal@xxxxxxx>
> Cc: Bart Van Assche <bvanassche@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 9cc5169cd478b ("block: Improve physical block alignment of split bios")
> Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
> ---
> block/blk-merge.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 5196dc145270..d7fef954d42f 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -154,7 +154,7 @@ static inline unsigned get_max_io_size(struct request_queue *q,
> if (max_sectors > start_offset)
> return max_sectors - start_offset;
>
> - return sectors & (lbs - 1);
> + return sectors & ~(lbs - 1);
> }
I think we agree that get_max_io_size() should never return zero. However, the above
change seems wrong to me because it will cause get_max_io_size() to return zero if
the logical block size is larger than 512 bytes and if sectors < lbs. How about
changing the return statement as follows (untested):
return max(sectors & (lbs - 1), sectors);
Thanks,
Bart.
