[PATCH 6.18 072/227] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

Greg Kroah-Hartman
2026-01-28T15:54:07Z

From: Joanne Koong <joannelkoong@gmail.com>

commit f9a49aa302a05e91ca01f69031cb79a0ea33031f upstream.

Above the while() loop in wait_sb_inodes(), we document that we must wait
for all pages under writeback for data integrity. Consequently, if a
mapping, like fuse, traditionally does not have data integrity semantics,
there is no need to wait at all; we can simply skip these inodes.

This restores fuse back to prior behavior where syncs are no-ops. This
fixes a user regression where if a system is running a faulty fuse server
that does not reply to issued write requests, this causes wait_sb_inodes()
to wait forever.

Link: https://lkml.kernel.org/r/20260105211737.4105620-2-joannelkoong@gmail.com
Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree")
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reported-by: Athul Krishna <athul.krishna.kr@protonmail.com>
Reported-by: J. Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Bernd Schubert <bschubert@ddn.com>
Tested-by: J. Neuschäfer <j.neuschaefer@gmx.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Bernd Schubert <bschubert@ddn.com>
Cc: Bonaccorso Salvatore <carnil@debian.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/fs-writeback.c | 7 ++++++-
fs/fuse/file.c | 4 +++-
include/linux/pagemap.h | 11 +++++++++++
3 files changed, 20 insertions(+), 2 deletions(-)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -2729,8 +2729,13 @@ static void wait_sb_inodes(struct super_
* The mapping can appear untagged while still on-list since we
* do not have the mapping lock. Skip it here, wb completion
* will remove it.
+ *
+ * If the mapping does not have data integrity semantics,
+ * there's no need to wait for the writeout to complete, as the
+ * mapping cannot guarantee that data is persistently stored.
*/
- if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
+ if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK) ||
+ mapping_no_data_integrity(mapping))
continue;

spin_unlock_irq(&sb->s_inode_wblist_lock);
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -3146,8 +3146,10 @@ void fuse_init_file_inode(struct inode *

inode->i_fop = &fuse_file_operations;
inode->i_data.a_ops = &fuse_file_aops;
- if (fc->writeback_cache)
+ if (fc->writeback_cache) {
mapping_set_writeback_may_deadlock_on_reclaim(&inode->i_data);
+ mapping_set_no_data_integrity(&inode->i_data);
+ }

INIT_LIST_HEAD(&fi->write_files);
INIT_LIST_HEAD(&fi->queued_writes);
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -213,6 +213,7 @@ enum mapping_flags {
AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM = 9,
AS_KERNEL_FILE = 10, /* mapping for a fake kernel file that shouldn't
account usage to user cgroups */
+ AS_NO_DATA_INTEGRITY = 11, /* no data integrity guarantees */
/* Bits 16-25 are used for FOLIO_ORDER */
AS_FOLIO_ORDER_BITS = 5,
AS_FOLIO_ORDER_MIN = 16,
@@ -348,6 +349,16 @@ static inline bool mapping_writeback_may
return test_bit(AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM, &mapping->flags);
}

+static inline void mapping_set_no_data_integrity(struct address_space *mapping)
+{
+ set_bit(AS_NO_DATA_INTEGRITY, &mapping->flags);
+}
+
+static inline bool mapping_no_data_integrity(const struct address_space *mapping)
+{
+ return test_bit(AS_NO_DATA_INTEGRITY, &mapping->flags);
+}
+
static inline gfp_t mapping_gfp_mask(const struct address_space *mapping)
{
return mapping->gfp_mask;