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: 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>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/gup.c b/mm/gup.c
index 551264407624..e2a39e30756d 100644
--- a/mm/gup.c
+++ b/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 *folio, int refs, unsigned int flags)
 			refs *= GUP_PIN_COUNTING_BIAS;
 	}
 
-	folio_put_refs(folio, refs);
+	if (!put_devmap_managed_page_refs(&folio->page, refs))
+		folio_put_refs(folio, refs);
 }
 
 /**