Re: [RFC PATCH 0/2] elevator: restore old io scheduler on failure in elevator_switch

[Christoph Hellwig]

On Fri, Nov 18, 2022 at 08:09:52PM +0800, Jinlong Chen wrote:
> elevator_switch contains the fallback logic in sq era, but it was removed
> when moving to mq (commit: a1ce35fa49852db60fc6e268038530be533c5b15),
> leaving the document mismatched with the behavior. As far as I can see,
> restoring the old io scheduler is more reasonable than just leaving the
> scheduler none, hence there is the series.

What failure scenariou can you think off where switching to the intended
schedule fails, but switching back to the previous one will succeed?