On Tue, Jul 05, 2022 at 02:18:19PM -0700, Andrew Morton wrote: > On Tue, 5 Jul 2022 20:35:32 +0800 Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote: > > > FSDAX page refcounts are 1-based, rather than 0-based: if refcount is > > 1, then the page is freed. The FSDAX pages can be pinned through GUP, > > then they will be unpinned via unpin_user_page() using a folio variant > > to put the page, however, folio variants did not consider this special > > case, the result will be to miss a wakeup event (like the user of > > __fuse_dax_break_layouts()). Since FSDAX pages are only possible get > > by GUP users, so fix GUP instead of folio_put() to lower overhead. > > > > What are the user visible runtime effects of this bug? "missing wake up event" seems pretty obvious to me? Something goes to sleep waiting for a page to become unused, and is never woken.
