kernel/linux.git/fs/ext4/fast_commit.c, branch v7.2-rc1

Merge tag 'ext4_for_linus-7.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4

2026-06-18T16:42:02+00:00

Pull ext4 updates from Ted Ts'o: - A major rework of the fast commit mechanism to avoid lock contention and deadlocks. We also export snapshot statistics in /proc/fs/ext4/*/fc_info - Performance optimization for directory hash computation by processing input in 4-byte chunks and removing function pointers, along with new KUnit tests for directory hash - Cleanups in JBD2 to remove special slabs and use kmalloc() instead - Various bug fixes, including: - Early validation of donor superblock in EXT4_IOC_MOVE_EXT to avoid cross-fs deadlock - Fix for a kernel BUG in ext4_write_inline_data_end under data=journal - Fix for a NULL dereference in jbd2_journal_dirty_metadata when handle is aborted - Fix for an underflow in JBD2 fast commit block initialization check - Fix for LOGFLUSH shutdown ordering to ensure ordered data writeback - Miscellaneous fixes for error path return values and KUnit assertions * tag 'ext4_for_linus-7.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: ext4: validate donor file superblock early in EXT4_IOC_MOVE_EXT ext4: fix kernel BUG in ext4_write_inline_data_end ext4: fix ERR_PTR(0) in ext4_mkdir() jbd2: remove special jbd2 slabs ext4: remove mention of PageWriteback ext4: improve str2hashbuf by processing 4-byte chunks and removing function pointers ext4: add Kunit coverage for directory hash computation ext4: fast commit: export snapshot stats in fc_info ext4: fast commit: add lock_updates tracepoint ext4: fast commit: avoid i_data_sem by dropping ext4_map_blocks() in snapshots ext4: fast commit: avoid self-deadlock in inode snapshotting ext4: fast commit: avoid waiting for FC_COMMITTING ext4: lockdep: handle i_data_sem subclassing for special inodes ext4: fast commit: snapshot inode state before writing log jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit() ext4: fix fast commit wait/wake bit mapping on 64-bit jbd2: check for aborted handle in jbd2_journal_dirty_metadata() ext4: Use %pe to print PTR_ERR() ext4: fix LOGFLUSH shutdown ordering to allow ordered-mode data writeback ext4: replace KUnit tests for memcmp() with KUNIT_ASSERT_MEMEQ()

ext4: Convert ext4_fc_submit_bh() to bh_submit()

2026-06-04T08:28:07+00:00

Avoid an extra indirect function call by converting ext4_end_buffer_io_sync() from bh_end_io_t to bio_end_io_t and calling bh_submit(). Signed-off-by: Matthew Wilcox (Oracle) Link: https://patch.msgid.link/20260528173150.1093780-14-willy@infradead.org Reviewed-by: Jan Kara Cc: linux-ext4@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

ext4: fast commit: export snapshot stats in fc_info

2026-06-03T14:26:36+00:00

Snapshot-based fast commit can fall back when the commit-time snapshot cannot be built (e.g. extent status cache misses). It is useful to quantify the updates-locked window and to see why snapshotting failed. Add best-effort snapshot counters to the ext4 superblock and extend /proc/fs/ext4//fc_info to report the number of snapshotted inodes and ranges, snapshot failure reasons, and the average/max time spent with journal updates locked. Signed-off-by: Li Chen Link: https://patch.msgid.link/20260515091829.194810-8-me@linux.beauty Signed-off-by: Theodore Ts'o

ext4: fast commit: add lock_updates tracepoint

2026-06-03T14:26:36+00:00

Commit-time fast commit snapshots run under jbd2_journal_lock_updates(), so it is useful to quantify the time spent with updates locked and to understand why snapshotting can fail. Add a new tracepoint, ext4_fc_lock_updates, reporting the time spent in the updates-locked window along with the number of snapshotted inodes and ranges. Record the first snapshot failure reason in a stable snap_err field for tooling. Signed-off-by: Li Chen Reviewed-by: Steven Rostedt (Google) Link: https://patch.msgid.link/20260515091829.194810-7-me@linux.beauty Signed-off-by: Theodore Ts'o

ext4: fast commit: avoid i_data_sem by dropping ext4_map_blocks() in snapshots

2026-06-03T14:26:36+00:00

Commit-time snapshots run under jbd2_journal_lock_updates(), so the work done there must stay bounded. The snapshot path still used ext4_map_blocks() to build data ranges. This can take i_data_sem and pulls the mapping code into the snapshot logic. Build inode data range snapshots from the extent status tree instead. The extent status tree is a cache, not an authoritative source. If the needed information is missing or unstable (e.g. delayed allocation), treat the transaction as fast commit ineligible and fall back to full commit. Also cap the number of inodes and ranges snapshotted per fast commit and allocate range records from a dedicated slab cache. The inode pointer array is allocated outside the updates-locked window. Testing: QEMU/KVM guest, virtio-pmem + dax, ext4 -O fast_commit, mounted dax,noatime. Ran python3 500x {4K write + fsync}, fallocate 256M, and python3 500x {creat + fsync(dir)} without lockdep splats or errors. Signed-off-by: Li Chen Link: https://patch.msgid.link/20260515091829.194810-6-me@linux.beauty Signed-off-by: Theodore Ts'o

ext4: fast commit: avoid self-deadlock in inode snapshotting

2026-06-03T14:26:35+00:00

ext4_fc_snapshot_inodes() used igrab()/iput() to pin inodes while building commit-time snapshots. With ext4_fc_del() waiting for EXT4_STATE_FC_COMMITTING, iput() can trigger ext4_clear_inode()->ext4_fc_del() in the commit thread and deadlock waiting for the fast commit to finish. ext4_fc_del() also has to re-check EXT4_STATE_FC_COMMITTING after waiting on EXT4_STATE_FC_FLUSHING_DATA. The commit thread clears FLUSHING_DATA before it sets COMMITTING, so a waiter woken from the flush wait must not delete the inode based on an old COMMITTING check. Avoid taking extra references. Collect inode pointers under s_fc_lock and rely on EXT4_STATE_FC_COMMITTING to pin inodes until ext4_fc_cleanup() clears the bit. Also set EXT4_STATE_FC_COMMITTING for create-only inodes referenced from the dentry update queue, and wake up waiters when ext4_fc_cleanup() clears the bit. Signed-off-by: Li Chen Link: https://patch.msgid.link/20260515091829.194810-5-me@linux.beauty Signed-off-by: Theodore Ts'o

ext4: fast commit: avoid waiting for FC_COMMITTING

2026-06-03T14:26:35+00:00

ext4_fc_track_inode() can be called while holding i_data_sem (e.g. fallocate). Waiting for EXT4_STATE_FC_COMMITTING in that case risks an ABBA deadlock: i_data_sem -> wait(FC_COMMITTING) vs FC_COMMITTING -> wait(i_data_sem) in the commit task. Now that fast commit snapshots inode state at commit time, updates during log writing do not need to block. Drop the wait and lockdep assertion in ext4_fc_track_inode(), and make ext4_fc_del() wait for FC_COMMITTING so an inode cannot be removed while the commit thread is still using it. When an inode is modified during a fast commit, mark it with EXT4_STATE_FC_REQUEUE so cleanup keeps it queued for the next fast commit. This is needed because jbd2_fc_end_commit() invokes the cleanup callback with tid == 0, so tid-based requeue logic would requeue every inode. Testing: tracepoint ext4:ext4_fc_commit_stop with two fsyncs in the same transaction. nblks is the number of journal blocks written for that fast commit. Before this change, the second fsync still wrote almost the same fast commit log (nblks 10->9), because tid == 0 in jbd2_fc_end_commit() caused the tid-based requeue logic to keep all inodes queued. After this change, only inodes modified during the commit are requeued, and the second fsync wrote a nearly empty fast commit (nblks 10->1). Signed-off-by: Li Chen Link: https://patch.msgid.link/20260515091829.194810-4-me@linux.beauty Signed-off-by: Theodore Ts'o

ext4: fast commit: snapshot inode state before writing log

2026-06-03T14:26:35+00:00

Fast commit writes inode metadata and data range updates after unlocking journal updates. New handles can start at that point, so the log writing path must not look at live inode state. Add a commit-time per-inode snapshot and populate it while journal updates are locked and existing handles are drained. Store the snapshot behind ext4_inode_info->i_fc_snap so ext4_inode_info only grows by one pointer. The snapshot contains a copy of the on-disk inode plus the data range records needed for fast commit TLVs. Snapshotting runs under jbd2_journal_lock_updates(). Avoid triggering I/O there by using ext4_get_inode_loc_noio() and falling back to full commit if the inode table block is not present or not uptodate. Log writing then only serializes the snapshot, so it no longer needs to call ext4_map_blocks() and take i_data_sem under s_fc_lock. The snapshot is installed and freed under s_fc_lock and is released from fast commit cleanup and inode eviction. Signed-off-by: Li Chen Link: https://patch.msgid.link/20260515091829.194810-2-me@linux.beauty Signed-off-by: Theodore Ts'o

ext4: fix fast commit wait/wake bit mapping on 64-bit

2026-06-03T14:21:49+00:00

On 64-bit, ext4 dynamic inode states live in the upper half of i_flags, and ext4_test_inode_state() applies the corresponding +32 offset. The fast-commit wait and wake paths open-coded the wait key with the raw EXT4_STATE_* value. Add small helpers for the state wait word and bit, and use them for the FC_COMMITTING and FC_FLUSHING_DATA waits so the wait key follows the same mapping as the state helpers. Fixes: 857d32f26181 ("ext4: rework fast commit commit path") Reported-by: Sashiko AI review Signed-off-by: Li Chen Reviewed-by: Baokun Li Reviewed-by: Zhang Yi Reviewed-by: Jan Kara Link: https://patch.msgid.link/20260513085818.552432-1-me@linux.beauty Signed-off-by: Theodore Ts'o

Merge tag 'ext4_for_linux-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4

2026-04-18T00:08:31+00:00

Pull ext4 updates from Ted Ts'o: - Refactor code paths involved with partial block zero-out in prearation for converting ext4 to use iomap for buffered writes - Remove use of d_alloc() from ext4 in preparation for the deprecation of this interface - Replace some J_ASSERTS with a journal abort so we can avoid a kernel panic for a localized file system error - Simplify various code paths in mballoc, move_extent, and fast commit - Fix rare deadlock in jbd2_journal_cancel_revoke() that can be triggered by generic/013 when blocksize < pagesize - Fix memory leak when releasing an extended attribute when its value is stored in an ea_inode - Fix various potential kunit test bugs in fs/ext4/extents.c - Fix potential out-of-bounds access in check_xattr() with a corrupted file system - Make the jbd2_inode dirty range tracking safe for lockless reads - Avoid a WARN_ON when writeback files due to a corrupted file system; we already print an ext4 warning indicatign that data will be lost, so the WARN_ON is not necessary and doesn't add any new information * tag 'ext4_for_linux-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: (37 commits) jbd2: fix deadlock in jbd2_journal_cancel_revoke() ext4: fix missing brelse() in ext4_xattr_inode_dec_ref_all() ext4: fix possible null-ptr-deref in mbt_kunit_exit() ext4: fix possible null-ptr-deref in extents_kunit_exit() ext4: fix the error handling process in extents_kunit_init). ext4: call deactivate_super() in extents_kunit_exit() ext4: fix miss unlock 'sb->s_umount' in extents_kunit_init() ext4: fix bounds check in check_xattrs() to prevent out-of-bounds access ext4: zero post-EOF partial block before appending write ext4: move pagecache_isize_extended() out of active handle ext4: remove ctime/mtime update from ext4_alloc_file_blocks() ext4: unify SYNC mode checks in fallocate paths ext4: ensure zeroed partial blocks are persisted in SYNC mode ext4: move zero partial block range functions out of active handle ext4: pass allocate range as loff_t to ext4_alloc_file_blocks() ext4: remove handle parameters from zero partial block functions ext4: move ordered data handling out of ext4_block_do_zero_range() ext4: rename ext4_block_zero_page_range() to ext4_block_zero_range() ext4: factor out journalled block zeroing range ext4: rename and extend ext4_block_truncate_page() ...