On 2/14/2023 6:19 AM, Linus Torvalds wrote:
On Mon, Feb 13, 2023 at 2:08 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:Kuan-Ying Lee (1): mm/gup: add folio to list when folio_isolate_lru() succeedUgh. I really hate fixes like this. The problem came from mis-understanding the return value of folio_isolate_lru(), and thinking that it was a boolean success/failure thing. It wasn't, it was an integer "success/errno" thing, and the sense of the test was wrong. So the patch is - if (!folio_isolate_lru(folio)) + if (folio_isolate_lru(folio)) continue; but at no point was the code *clarified*. Wouldn't it have been much better to write the new code to be if (folio_isolate_lru(folio) < 0) continue; to actually make it clear that this is a "negative error return check". I've pulled this, but I really think that when somebody notices that we had a silly bug because of a misunderstanding like this, it's not just that the bug should be fixed, the code should also be *clarified* at the same time.
Yes, agree, I need to check the return value of folio_isolate_lru() every time when looking at the code. I can help to create a patch to make it clear for all users.
