+ mm-fix-missing-wake-up-event-for-fsdax-pages.patch added to mm-hotfixes-unstable branch

+ mm-fix-missing-wake-up-event-for-fsdax-pages.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: fix missing wake-up event for FSDAX pages
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-fix-missing-wake-up-event-for-fsdax-pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-missing-wake-up-event-for-fsdax-pages.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm: fix missing wake-up event for FSDAX pages
Date: Tue, 5 Jul 2022 20:35:32 +0800

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.

Link: https://lkml.kernel.org/r/20220705123532.283-1-songmuchun@bytedance.com
Fixes: d8ddc099c6b3 ("mm/gup: Add gup_put_folio()")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h |   14 +++++++++-----
 mm/gup.c           |    6 ++++--
 mm/memremap.c      |    6 +++---
 3 files changed, 16 insertions(+), 10 deletions(-)

--- a/include/linux/mm.h~mm-fix-missing-wake-up-event-for-fsdax-pages
+++ a/include/linux/mm.h
@@ -1130,23 +1130,27 @@ static inline bool is_zone_movable_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_refs(struct page *page, int refs);
+static inline bool put_devmap_managed_page_refs(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_refs(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_refs(struct page *page, int refs)
 {
 	return false;
 }
 #endif /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */
 
+static inline bool put_devmap_managed_page(struct page *page)
+{
+	return put_devmap_managed_page_refs(page, 1);
+}
+
 /* 127: arbitrary random number, small enough to assemble well */
 #define folio_ref_zero_or_close_to_overflow(folio) \
 	((unsigned int) folio_ref_count(folio) + 127u <= 127u)
--- a/mm/gup.c~mm-fix-missing-wake-up-event-for-fsdax-pages
+++ a/mm/gup.c
@@ -87,7 +87,8 @@ retry:
 	 * belongs to this folio.
 	 */
 	if (unlikely(page_folio(page) != folio)) {
-		folio_put_refs(folio, refs);
+		if (!put_devmap_managed_page_refs(&folio->page, refs))
+			folio_put_refs(folio, refs);
 		goto retry;
 	}
 
@@ -176,7 +177,8 @@ static void gup_put_folio(struct folio *
 			refs *= GUP_PIN_COUNTING_BIAS;
 	}
 
-	folio_put_refs(folio, refs);
+	if (!put_devmap_managed_page_refs(&folio->page, refs))
+		folio_put_refs(folio, refs);
 }
 
 /**
--- a/mm/memremap.c~mm-fix-missing-wake-up-event-for-fsdax-pages
+++ a/mm/memremap.c
@@ -499,7 +499,7 @@ void free_zone_device_page(struct page *
 }
 
 #ifdef CONFIG_FS_DAX
-bool __put_devmap_managed_page(struct page *page)
+bool __put_devmap_managed_page_refs(struct page *page, int refs)
 {
 	if (page->pgmap->type != MEMORY_DEVICE_FS_DAX)
 		return false;
@@ -509,9 +509,9 @@ bool __put_devmap_managed_page(struct pa
 	 * 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;
 }
-EXPORT_SYMBOL(__put_devmap_managed_page);
+EXPORT_SYMBOL(__put_devmap_managed_page_refs);
 #endif /* CONFIG_FS_DAX */
_

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-fix-missing-wake-up-event-for-fsdax-pages.patch
mm-memcontrol-remove-dead-code-and-comments.patch
mm-rename-unlock_page_lruvec_irq-_irqrestore-to-lruvec_unlock_irq-_irqrestore.patch
mm-memcontrol-prepare-objcg-api-for-non-kmem-usage.patch
mm-memcontrol-make-lruvec-lock-safe-when-lru-pages-are-reparented.patch
mm-vmscan-rework-move_pages_to_lru.patch
mm-thp-make-split-queue-lock-safe-when-lru-pages-are-reparented.patch
mm-memcontrol-make-all-the-callers-of-foliopage_memcg-safe.patch
mm-memcontrol-introduce-memcg_reparent_ops.patch
mm-memcontrol-use-obj_cgroup-apis-to-charge-the-lru-pages.patch
mm-lru-add-vm_warn_on_once_folio-to-lru-maintenance-function.patch
mm-hugetlb_vmemmap-delete-hugetlb_optimize_vmemmap_enabled.patch
mm-hugetlb_vmemmap-optimize-vmemmap_optimize_mode-handling.patch
mm-hugetlb_vmemmap-introduce-the-name-hvo.patch
mm-hugetlb_vmemmap-move-vmemmap-code-related-to-hugetlb-to-hugetlb_vmemmapc.patch
mm-hugetlb_vmemmap-replace-early_param-with-core_param.patch
mm-hugetlb_vmemmap-improve-hugetlb_vmemmap-code-readability.patch
mm-hugetlb_vmemmap-move-code-comments-to-vmemmap_deduprst.patch
mm-hugetlb_vmemmap-use-ptrs_per_pte-instead-of-pmd_size-page_size.patch