From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AFE19C43334 for ; Mon, 4 Jul 2022 10:38:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233575AbiGDKig (ORCPT ); Mon, 4 Jul 2022 06:38:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34534 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233477AbiGDKif (ORCPT ); Mon, 4 Jul 2022 06:38:35 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF2AF2AF0; Mon, 4 Jul 2022 03:38:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=bgFpDRJ1phHQqdCoJBko0cJC9ngsJhc8l5GKh4nATgo=; b=rSgWnvQEmiowdltF5/el1vzXCe EouJ0fQsqVyuBzwEgkUO/ew48ICBo4l6H1cJc+N/MR1v+uMNj3mbLq0RDNvRygBYzO3xqLdtaWTce JqeMO6RsgfJ+n0AeIFuo1oWQuW9yyBtXVqlGlZ2orNkHOJZRGlyNAf2D5kg5iMm0959zGWd13jboR qpX+oF9PeFyB3pFOqV9dUr3NVFQLBAp9nJ3Of3Kx+0fwekZlbOisV7XugG9/ZzvX9gwnarHiOmMxc 4/AUFNBs96GW3W+jWK6WEZYSAUhxYZFmNJnvsltMLtdytDmbe0jQe97UrRuPLt4emehZsKnv8V6UD 19e6+GEw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1o8JT6-00HBd7-Bw; Mon, 04 Jul 2022 10:38:16 +0000 Date: Mon, 4 Jul 2022 11:38:16 +0100 From: Matthew Wilcox To: Muchun Song Cc: akpm@linux-foundation.org, jgg@ziepe.ca, jhubbard@nvidia.com, william.kucharski@oracle.com, dan.j.williams@intel.com, jack@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev Subject: Re: [PATCH] mm: fix missing wake-up event for FSDAX pages Message-ID: References: <20220704074054.32310-1-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220704074054.32310-1-songmuchun@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Jul 04, 2022 at 03:40:54PM +0800, Muchun Song 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()). Argh, no. The 1-based refcounts are a blight on the entire kernel. They need to go away, not be pushed into folios as well. I think we're close to having that fixed, but until then, this should do the trick? diff --git a/include/linux/mm.h b/include/linux/mm.h index cc98ab012a9b..4cef5e0f78b6 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1129,18 +1129,18 @@ static inline bool is_zone_movable_page(const struct page *page) #if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_FS_DAX) DECLARE_STATIC_KEY_FALSE(devmap_managed_key); -bool __put_devmap_managed_page(struct page *page); -static inline bool put_devmap_managed_page(struct page *page) +bool __put_devmap_managed_page(struct page *page, int refs); +static inline bool put_devmap_managed_page(struct page *page, int refs) { if (!static_branch_unlikely(&devmap_managed_key)) return false; if (!is_zone_device_page(page)) return false; - return __put_devmap_managed_page(page); + return __put_devmap_managed_page(page, refs); } #else /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */ -static inline bool put_devmap_managed_page(struct page *page) +static inline bool put_devmap_managed_page(struct page *page, int refs) { return false; } @@ -1246,7 +1246,7 @@ static inline void put_page(struct page *page) * For some devmap managed pages we need to catch refcount transition * from 2 to 1: */ - if (put_devmap_managed_page(&folio->page)) + if (put_devmap_managed_page(&folio->page, 1)) return; folio_put(folio); } diff --git a/mm/gup.c b/mm/gup.c index d1132b39aa8f..28df02121c78 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -88,7 +88,8 @@ static inline struct folio *try_get_folio(struct page *page, int refs) * belongs to this folio. */ if (unlikely(page_folio(page) != folio)) { - folio_put_refs(folio, refs); + if (!put_devmap_managed_page(&folio->page, refs)) + folio_put_refs(folio, refs); goto retry; } @@ -177,6 +178,8 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags) refs *= GUP_PIN_COUNTING_BIAS; } + if (put_devmap_managed_page(&folio->page, refs)) + return; folio_put_refs(folio, refs); } diff --git a/mm/memremap.c b/mm/memremap.c index b870a659eee6..b25e40e3a11e 100644 --- a/mm/memremap.c +++ b/mm/memremap.c @@ -499,7 +499,7 @@ void free_zone_device_page(struct page *page) } #ifdef CONFIG_FS_DAX -bool __put_devmap_managed_page(struct page *page) +bool __put_devmap_managed_page(struct page *page, int refs) { if (page->pgmap->type != MEMORY_DEVICE_FS_DAX) return false; @@ -509,7 +509,7 @@ bool __put_devmap_managed_page(struct page *page) * refcount is 1, then the page is free and the refcount is * stable because nobody holds a reference on the page. */ - if (page_ref_dec_return(page) == 1) + if (page_ref_sub_return(page, refs) == 1) wake_up_var(&page->_refcount); return true; } diff --git a/mm/swap.c b/mm/swap.c index c6194cfa2af6..94e42a9bab92 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -960,7 +960,7 @@ void release_pages(struct page **pages, int nr) unlock_page_lruvec_irqrestore(lruvec, flags); lruvec = NULL; } - if (put_devmap_managed_page(&folio->page)) + if (put_devmap_managed_page(&folio->page, 1)) continue; if (folio_put_testzero(folio)) free_zone_device_page(&folio->page);