On Mon, Aug 17, 2020 at 06:01:30PM +0800, Ming Lei wrote:
> In case of block device backend, if the backend supports write zeros, the
> loop device will set queue flag of QUEUE_FLAG_DISCARD. However,
> limits.discard_granularity isn't setup, and this way is wrong,
> see the following description in Documentation/ABI/testing/sysfs-block:
>
> A discard_granularity of 0 means that the device does not support
> discard functionality.
>
> Especially 9b15d109a6b2 ("block: improve discard bio alignment in
> __blkdev_issue_discard()") starts to take q->limits.discard_granularity
> for computing max discard sectors. And zero discard granularity may cause
> kernel oops, or fail discard request even though the loop queue claims
> discard support via QUEUE_FLAG_DISCARD.
>
> Fix the issue by setup discard granularity and alignment.
This patch looks good:
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
If you have a few spare cycles, can you kill QUEUE_FLAG_DISCARD and
just key off discard support based on checking discard_granularity to
avoid problems like this in the future?
