If cow_file_range() succeed to submit bio for a part of the given region, then got an error (e.g. ENOSPC) for another part, cow_file_range() returns pages with a mixed lock status: locked for the succeed part and unlocked for the errored part.
We can't return with an error leaving the pages locked. But, we don't know where the locked pages are.
If cow_file_range() succeed to submit bio for a part of the given region, then got an error (e.g. ENOSPC) for another part, cow_file_range() returns pages with a mixed lock status: locked for the succeed part and unlocked for the errored part.
We can't return with an error leaving the pages locked. But, we don't know where the locked pages are.
This issue can be jointly solved with #14.