kernel/linux.git/fs/fuse/file.c, branch v6.19.11

writeback: don't block sync for filesystems with no data integrity guarantees

2026-04-02T11:25:43+00:00

commit 76f9377cd2ab7a9220c25d33940d9ca20d368172 upstream. Add a SB_I_NO_DATA_INTEGRITY superblock flag for filesystems that cannot guarantee data persistence on sync (eg fuse). For superblocks with this flag set, sync kicks off writeback of dirty inodes but does not wait for the flusher threads to complete the writeback. This replaces the per-inode AS_NO_DATA_INTEGRITY mapping flag added in commit f9a49aa302a0 ("fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()"). The flag belongs at the superblock level because data integrity is a filesystem-wide property, not a per-inode one. Having this flag at the superblock level also allows us to skip having to iterate every dirty inode in wait_sb_inodes() only to skip each inode individually. Prior to this commit, mappings with no data integrity guarantees skipped waiting on writeback completion but still waited on the flusher threads to finish initiating the writeback. Waiting on the flusher threads is unnecessary. This commit kicks off writeback but does not wait on the flusher threads. This change properly addresses a recent report [1] for a suspend-to-RAM hang seen on fuse-overlayfs that was caused by waiting on the flusher threads to finish: Workqueue: pm_fs_sync pm_fs_sync_work_fn Call Trace: __schedule+0x457/0x1720 schedule+0x27/0xd0 wb_wait_for_completion+0x97/0xe0 sync_inodes_sb+0xf8/0x2e0 __iterate_supers+0xdc/0x160 ksys_sync+0x43/0xb0 pm_fs_sync_work_fn+0x17/0xa0 process_one_work+0x193/0x350 worker_thread+0x1a1/0x310 kthread+0xfc/0x240 ret_from_fork+0x243/0x280 ret_from_fork_asm+0x1a/0x30 On fuse this is problematic because there are paths that may cause the flusher thread to block (eg if systemd freezes the user session cgroups first, which freezes the fuse daemon, before invoking the kernel suspend. The kernel suspend triggers ->write_node() which on fuse issues a synchronous setattr request, which cannot be processed since the daemon is frozen. Or if the daemon is buggy and cannot properly complete writeback, initiating writeback on a dirty folio already under writeback leads to writeback_get_folio() -> folio_prepare_writeback() -> unconditional wait on writeback to finish, which will cause a hang). This commit restores fuse to its prior behavior before tmp folios were removed, where sync was essentially a no-op. [1] https://lore.kernel.org/linux-fsdevel/CAJnrk1a-asuvfrbKXbEwwDSctvemF+6zfhdnuzO65Pt8HsFSRw@mail.gmail.com/T/#m632c4648e9cafc4239299887109ebd880ac6c5c1 Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree") Reported-by: John Cc: stable@vger.kernel.org Signed-off-by: Joanne Koong Link: https://patch.msgid.link/20260320005145.2483161-2-joannelkoong@gmail.com Reviewed-by: Jan Kara Reviewed-by: David Hildenbrand (Arm) Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman

fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

2026-01-19T20:30:01+00:00

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 Reported-by: Athul Krishna Reported-by: J. Neuschäfer Reviewed-by: Bernd Schubert Tested-by: J. Neuschäfer Cc: Alexander Viro Cc: Bernd Schubert Cc: Bonaccorso Salvatore Cc: Christian Brauner Cc: David Hildenbrand Cc: Jan Kara Cc: "Liam R. Howlett" Cc: Lorenzo Stoakes Cc: "Matthew Wilcox (Oracle)" Cc: Michal Hocko Cc: Mike Rapoport Cc: Miklos Szeredi Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton

Merge tag 'fuse-update-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse

2025-12-05T23:25:13+00:00

Pull fuse updates from Miklos Szeredi: - Add mechanism for cleaning out unused, stale dentries; controlled via a module option (Luis Henriques) - Fix various bugs - Cleanups * tag 'fuse-update-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse: fuse: Uninitialized variable in fuse_epoch_work() fuse: fix io-uring list corruption for terminated non-committed requests fuse: signal that a fuse inode should exhibit local fs behaviors fuse: Always flush the page cache before FOPEN_DIRECT_IO write fuse: Invalidate the page cache after FOPEN_DIRECT_IO write fuse: rename 'namelen' to 'namesize' fuse: use strscpy instead of strcpy fuse: refactor fuse_conn_put() to remove negative logic. fuse: new work queue to invalidate dentries from old epochs fuse: new work queue to periodically invalidate expired dentries dcache: export shrink_dentry_list() and add new helper d_dispose_if_unused() fuse: add WARN_ON and comment for RCU revalidate fuse: Fix whitespace for fuse_uring_args_to_ring() comment fuse: missing copy_finish in fuse-over-io-uring argument copies fuse: fix readahead reclaim deadlock

fuse: Always flush the page cache before FOPEN_DIRECT_IO write

2025-11-13T13:54:05+00:00

This was done as condition on direct_io_allow_mmap, but I believe this is not right, as a file might be open two times - once with write-back enabled another time with FOPEN_DIRECT_IO. Signed-off-by: Bernd Schubert Signed-off-by: Miklos Szeredi

fuse: Invalidate the page cache after FOPEN_DIRECT_IO write

2025-11-13T13:54:05+00:00

generic_file_direct_write() also does this and has a large comment about. Reproducer here is xfstest's generic/209, which is exactly to have competing DIO write and cached IO read. Signed-off-by: Bernd Schubert Signed-off-by: Miklos Szeredi

iomap: simplify ->read_folio_range() error handling for reads

2025-11-12T09:50:32+00:00

Instead of requiring that the caller calls iomap_finish_folio_read() even if the ->read_folio_range() callback returns an error, account for this internally in iomap instead, which makes the interface simpler and makes it match writeback's ->read_folio_range() error handling expectations. Signed-off-by: Joanne Koong Link: https://patch.msgid.link/20251111193658.3495942-6-joannelkoong@gmail.com Reviewed-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Christian Brauner

iomap: optimize pending async writeback accounting

2025-11-12T09:50:32+00:00

Pending writebacks must be accounted for to determine when all requests have completed and writeback on the folio should be ended. Currently this is done by atomically incrementing ifs->write_bytes_pending for every range to be written back. Instead, the number of atomic operations can be minimized by setting ifs->write_bytes_pending to the folio size, internally tracking how many bytes are written back asynchronously, and then after sending off all the requests, decrementing ifs->write_bytes_pending by the number of bytes not written back asynchronously. Now, for N ranges written back, only N + 2 atomic operations are required instead of 2N + 2. Signed-off-by: Joanne Koong Link: https://patch.msgid.link/20251111193658.3495942-5-joannelkoong@gmail.com Reviewed-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Christian Brauner

fuse: fix readahead reclaim deadlock

2025-11-11T15:04:45+00:00

Commit e26ee4efbc79 ("fuse: allocate ff->release_args only if release is needed") skips allocating ff->release_args if the server does not implement open. However in doing so, fuse_prepare_release() now skips grabbing the reference on the inode, which makes it possible for an inode to be evicted from the dcache while there are inflight readahead requests. This causes a deadlock if the server triggers reclaim while servicing the readahead request and reclaim attempts to evict the inode of the file being read ahead. Since the folio is locked during readahead, when reclaim evicts the fuse inode and fuse_evict_inode() attempts to remove all folios associated with the inode from the page cache (truncate_inode_pages_range()), reclaim will block forever waiting for the lock since readahead cannot relinquish the lock because it is itself blocked in reclaim: >>> stack_trace(1504735) folio_wait_bit_common (mm/filemap.c:1308:4) folio_lock (./include/linux/pagemap.h:1052:3) truncate_inode_pages_range (mm/truncate.c:336:10) fuse_evict_inode (fs/fuse/inode.c:161:2) evict (fs/inode.c:704:3) dentry_unlink_inode (fs/dcache.c:412:3) __dentry_kill (fs/dcache.c:615:3) shrink_kill (fs/dcache.c:1060:12) shrink_dentry_list (fs/dcache.c:1087:3) prune_dcache_sb (fs/dcache.c:1168:2) super_cache_scan (fs/super.c:221:10) do_shrink_slab (mm/shrinker.c:435:9) shrink_slab (mm/shrinker.c:626:10) shrink_node (mm/vmscan.c:5951:2) shrink_zones (mm/vmscan.c:6195:3) do_try_to_free_pages (mm/vmscan.c:6257:3) do_swap_page (mm/memory.c:4136:11) handle_pte_fault (mm/memory.c:5562:10) handle_mm_fault (mm/memory.c:5870:9) do_user_addr_fault (arch/x86/mm/fault.c:1338:10) handle_page_fault (arch/x86/mm/fault.c:1481:3) exc_page_fault (arch/x86/mm/fault.c:1539:2) asm_exc_page_fault+0x22/0x27 Fix this deadlock by allocating ff->release_args and grabbing the reference on the inode when preparing the file for release even if the server does not implement open. The inode reference will be dropped when the last reference on the fuse file is dropped (see fuse_file_put() -> fuse_release_end()). Fixes: e26ee4efbc79 ("fuse: allocate ff->release_args only if release is needed") Cc: stable@vger.kernel.org Signed-off-by: Joanne Koong Reported-by: Omar Sandoval Signed-off-by: Miklos Szeredi

fuse: use iomap for readahead

2025-11-05T11:57:24+00:00

Do readahead in fuse using iomap. This gives us granular uptodate tracking for large folios, which optimizes how much data needs to be read in. If some portions of the folio are already uptodate (eg through a prior write), we only need to read in the non-uptodate portions. Signed-off-by: Joanne Koong Reviewed-by: Darrick J. Wong Signed-off-by: Christian Brauner

fuse: use iomap for read_folio

2025-11-05T11:57:23+00:00

Read folio data into the page cache using iomap. This gives us granular uptodate tracking for large folios, which optimizes how much data needs to be read in. If some portions of the folio are already uptodate (eg through a prior write), we only need to read in the non-uptodate portions. Signed-off-by: Joanne Koong Reviewed-by: Darrick J. Wong Signed-off-by: Christian Brauner