Linus Torvalds has announced the fourth release candidate (RC4) for the Linux Kernel 6.16. Despite a fairly large merge window earlier in the cycle, this week's update looks stable and focused.
If you're testing the Kernel 6.16 series or just keeping an eye on development, RC4 brings useful updates across filesystems, drivers, and core kernel subsystems.
What's New in Linux Kernel 6.16 RC4?
As Linus noted in the Kernel 6.16-rc4 announcement mail, RC4 is roughly divided into three parts:
- Filesystem updates
- Driver changes
- Miscellaneous fixes
Let's look at each in more detail.
1. Filesystem Updates: Bcachefs Leads the Way
About one-third of the RC4 changes touch the filesystem stack. Most of these are focused on bcachefs, the new copy-on-write filesystem aiming to compete with Btrfs and ZFS.
Key bcachefs updates include:
- Better journaling and recovery handling.
- Fixes for race conditions, NULL dereferences, and snapshot edge cases.
- Enhanced error messages and diagnostics in
fsck.
Other notable filesystem changes:
- Btrfs: Multiple fixes for error reporting, memory handling, and delayed references.
- SMB and CIFS: Fixes related to memory safety and iterator logic.
- F2FS: Minor fixes, including zeroing pages beyond EOF.
2. Driver Updates: Device Mapper and AMD GPU Stand Out
The driver side also accounts for about a third of the patchset. These updates touch a wide range of subsystems:
- Device Mapper: A few patches were reverted due to performance regressions.
- Graphics: AMDGPU and Intel display drivers got several fixes, especially around firmware compatibility and DisplayPort handling.
- Sound: Fixes for mic mute LEDs and audio offload on Qualcomm platforms.
- Bluetooth and Wi-Fi: Improvements to suspend/resume stability and interrupt handling.
- NVMe: Refactored atomic write unit detection and fixed size validation for atomic operations.
- Networking: Stack usage reductions in TLV processing and fixes for TCP checksum calculations in selftests.
- SCSI: Several patches to improve stability in error-prone scenarios.
3. Miscellaneous Changes: Architecture Fixes, Docs, and Testing
The final third of RC4 includes a variety of changes, fixes and improvements:
- Memory Management: Resolved a softlockup during THP (Transparent Huge Pages) swap-in and fixed userfaultfd race conditions with swap caches.
- RISC-V: Corrected inline assembly constraints in the vDSO getrandom wrapper and fixed runtime constant support for NOMMU kernels.
- io_uring: Fixed resource leaks, folio unpinning errors, and improved buffer handling.
- HID: Added quirks for HP, Lenovo, and Wacom devices, along with fixes for mute LED controls.
- Architecture fixes: LoongArch, x86, and UM saw cleanup and patching, mostly around warnings, memory alignment, and pointer safety.
- Selftests: Memory management and BPF selftests received more coverage and timeouts were adjusted.
- Documentation: Several typos and formatting issues in the docs were corrected.
The Kernel 6.16 Looks Stable So Far
Despite the wide scope of changes in RC4, Torvalds described the release as "calm". This suggests that the changes are mostly routine, with no major regressions or urgent breakage reported so far.
He also reminds testers to keep running RC builds to spot any issues early.
Try Linux Kernel 6.16 RC4
Linux 6.16-rc4 is shaping up well. The filesystem fixes, driver improvements, and overall stability suggest that 6.16 may be a solid, balanced release once it reaches final form.
If you're running tests on -rc kernels, now is a good time to try RC4 and report bugs. You can download Linux Kernel 6.16 RC4 from the Kernel.org website or the Linus Torvalds's git tree.
For the rest of us, it’s an early glimpse at what's coming to mainline in the weeks ahead.
