>>>> It's trying to split some pmd-mapped THPs then checking and finding that >>>> they are not split. The split is requested via >>>> /sys/kernel/debug/split_huge_pages, which I believe ends up in this function >>>> you are modifying here. Although I'll admit that looking at the change, >>>> there is nothing obviously wrong! Any ideas? >>> >>> Nothing jumps at me as well. Let me fire up the debugger :) >> >> Ah, very likely the can_split_folio() check expects a raised refcount >> already. > > Indeed, the following does the trick! Thanks Ryan, I could have sworn > I ran that selftest as well. Ahha! Thanks for sorting so quickly!