On Mon, Aug 05, 2024 at 04:00:23PM +0200, Jan Kara wrote: > Actually add Matthew to CC ;) It's OK, I was reading. FWIW, I agree with Dave; the locking complexity in this patch was horrendous. I was going to get to the same critique he had, but I first wanted to understand what the thought process was. > > > Ha, right, I missed the comments of this function, it means that there are > > > some special callers that hold table lock instead of folio lock, is it > > > pte_alloc_map_lock? > > > > > > I checked all the filesystem related callers and didn't find any real > > > caller that mark folio dirty without holding folio lock and that could > > > affect current filesystems which are using iomap framework, it's just > > > a potential possibility in the future, am I right? Filesystems are normally quite capable of taking the folio lock to prevent truncation. It's the MM code that needs the "or holding the page table lock" get-out clause. I forget exactly which callers it is; I worked through them a few times. It's not hard to put a WARN_ON_RATELIMIT() into folio_mark_dirty() and get a good sampling. There's also a "or holding a buffer_head locked" get-out clause that I'm not sure is documented anywhere, but obviously that doesn't apply to the iomap code. > > There used to be quite a few places doing that. Now that I've checked all > > places I was aware of got actually converted to call folio_mark_dirty() under > > a folio lock (in particular all the cases happening on IO completion, folio > > unmap etc.). Matthew, are you aware of any place where folio_mark_dirty() > > would be called for regular file page cache (block device page cache is in a > > different situation obviously) without folio lock held? Yes, the MM code definitely applies to regular files as well as block devices.
