Commit f4f451a1 authored by Muchun Song's avatar Muchun Song Committed by Andrew Morton
Browse files

mm: fix missing wake-up event for FSDAX pages 

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()).  This results in a task being permanently
stuck in TASK_INTERRUPTIBLE state.

Since FSDAX pages are only possibly obtained 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: d8ddc099 ("mm/gup: Add gup_put_folio()")
Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Suggested-by: default avatarMatthew 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 3fe2895c

include/linux/mm.h

+9 −5
Original line number Diff line number Diff line
@@ -1130,23 +1130,27 @@ 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_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)

mm/gup.c

+4 −2
Original line number Diff line number Diff line
@@ -87,6 +87,7 @@ static inline struct folio *try_get_folio(struct page *page, int refs) 
	 * belongs to this folio.

	 */

	if (unlikely(page_folio(page) != folio)) {

		if (!put_devmap_managed_page_refs(&folio->page, refs))

			folio_put_refs(folio, refs);

		goto retry;

	}
@@ -176,6 +177,7 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags) 
			refs *= GUP_PIN_COUNTING_BIAS;

	}



	if (!put_devmap_managed_page_refs(&folio->page, refs))

		folio_put_refs(folio, refs);

}

mm/memremap.c

+3 −3
Original line number Diff line number Diff line
@@ -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_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 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;

}

EXPORT_SYMBOL(__put_devmap_managed_page);

EXPORT_SYMBOL(__put_devmap_managed_page_refs);

#endif /* CONFIG_FS_DAX */