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Date: Tue, 5 Jul 2022 14:18:19 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Muchun Song <songmuchun@...edance.com> Cc: willy@...radead.org, jgg@...pe.ca, jhubbard@...dia.com, william.kucharski@...cle.com, dan.j.williams@...el.com, jack@...e.cz, linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev, stable@...r.kernel.org Subject: Re: [PATCH v2] mm: fix missing wake-up event for FSDAX pages On Tue, 5 Jul 2022 20:35:32 +0800 Muchun Song <songmuchun@...edance.com> 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?
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