On 12/15/25 04:00, Joanne Koong wrote:

Skip waiting on writeback for inodes that belong to mappings that do not have data integrity guarantees (denoted by the AS_NO_DATA_INTEGRITY mapping flag).

This restores fuse back to prior behavior where syncs are no-ops. This is needed because otherwise, if a system is running a faulty fuse server that does not reply to issued write requests, this will cause wait_sb_inodes() to wait forever.

Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree") Reported-by: Athul Krishna athul.krishna.kr@protonmail.com Reported-by: J. Neuschäfer j.neuschaefer@gmx.net Cc: stable@vger.kernel.org Signed-off-by: Joanne Koong joannelkoong@gmail.com

---

fs/fs-writeback.c | 3 ++- fs/fuse/file.c | 4 +++- include/linux/pagemap.h | 11 +++++++++++ 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 6800886c4d10..ab2e279ed3c2 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -2751,7 +2751,8 @@ static void wait_sb_inodes(struct super_block *sb) * do not have the mapping lock. Skip it here, wb completion * will remove it. */

• 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); diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 01bc894e9c2b..3b2a171e652f 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -3200,8 +3200,10 @@ void fuse_init_file_inode(struct inode *inode, unsigned int flags) 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);
  

• }

For a future commit, maybe we could add a FUSE_INIT flag that allows privileged fuse server to not set this? Maybe even in combination with an enforced request timeout?

INIT_LIST_HEAD(&fi->write_files); INIT_LIST_HEAD(&fi->queued_writes); diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 31a848485ad9..ec442af3f886 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -210,6 +210,7 @@ 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,

@@ -345,6 +346,16 @@ static inline bool mapping_writeback_may_deadlock_on_reclaim(const struct addres 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;

Reviewed-by: Bernd Schubert bschubert@ddn.com