[PATCH 1/2] mm: add filemap_lock_folio_nowait helper

[Jinchao Wang <wangjinchao600@gmail.com>]

Introduce filemap_lock_folio_nowait() to allow non-blocking folio lock
attempts using FGP_NOWAIT. This allows callers to avoid AB-BA deadlocks
by dropping higher-level locks when a folio is already locked.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 include/linux/pagemap.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 31a848485ad9..b9d818a9409b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -825,6 +825,12 @@ static inline struct folio *filemap_lock_folio(struct address_space *mapping,
 	return __filemap_get_folio(mapping, index, FGP_LOCK, 0);
 }
 
+static inline struct folio *filemap_lock_folio_nowait(struct address_space *mapping,
+						      pgoff_t index)
+{
+	return __filemap_get_folio(mapping, index, FGP_LOCK | FGP_NOWAIT, 0);
+}
+
 /**
  * filemap_grab_folio - grab a folio from the page cache
  * @mapping: The address space to search
-- 
2.43.0