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
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx
Fixes: d8ddc099c6b3 ("mm/gup: Add gup_put_folio()")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxx 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
