fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

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>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 6800886c4d1047b28c5c07613a1a1b256e982a95..baa2f2141146610e31cbe3a46cff8beb0490d389 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -2750,8 +2750,13 @@ static void wait_sb_inodes(struct super_block *sb)
                 * 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);

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 01bc894e9c2baee49a9b8ddb7ab036244e574b37..3b2a171e652f0c9dd1c9e37253d3d3e88caab148 100644 (file)
--- 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);
+       }
 
        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 31a848485ad9d9850d37185418349b89e6efe420..ec442af3f88613ad48ae2152ab2d528341848cd0 100644 (file)
--- 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;