Got soft lockup CPU if dell_uart_backlight is probed

[AceLan Kao]

[Impact]
After v6.5, calls tty->driver->ops->chars_in_buffer() may lead to a deadlock and got soft lockup error.

[Fix]
Do not use this function in dell-uart-backlight driver.
Try using tty->driver->ops->flush_chars() to send out the commands.

[Test Case]
1. Boot up Dell AIO system with v6.5 kernel.
2. Check dmesg and make sure there is no soft lockup error message in it.

[Where problems could occur]
There is no functional change, even if uart_flush_chars() doesn't do what we expected, the driver should be able to keep workings, as the backlight commands is only 3 or 4 bytes short and has little chance to stay in the queue partially.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-oem-6.5 - 6.5.0-1003.3

---------------
linux-oem-6.5 (6.5.0-1003.3) jammy; urgency=medium

  * jammy/linux-oem-6.5: 6.5.0-1003.3 -proposed tracker (LP: #2033279)

  * Packaging resync (LP: #1786013)
    - [Packaging] update Ubuntu.md
    - [Packaging] update update.conf

  * Resync CI Runner Configuration (LP: #2024199)
    - [CI] resync ci configuration
    - [CI] resync ci configuration

  * i915: Backport some fixes for Meteor Lake, vol2 (LP: #2032781)
    - drm/i915/gsc: fixes and updates for GSC memory allocation
    - drm/i915/mtl/gsc: extract release and security versions from the gsc binary
    - drm/i915/mtl/gsc: query the GSC FW for its compatibility version
    - drm/i915/mtl/gsc: Add a gsc_info debugfs
    - drm/i915/gsc: Fix intel_gsc_uc_fw_proxy_init_done with directed wakerefs
    - drm/i915/display: Do not use stolen on MTL
    - drm/i915/huc: check HuC and GuC version compatibility on MTL
    - drm/i915/selftest/gsc: Ensure GSC Proxy init completes before selftests
    - drm/i915/color: Upscale degamma values for MTL
    - drm/i915/color: Downscale degamma lut values read from hardware
    - drm/i915/gt: Simplify shmem_create_from_object map_type selection
    - SAUCE: drm/i915: Make i915_coherent_map_type GT-centric
    - drm/i915/gt: Apply workaround 22016122933 correctly

  * ubuntu_bpf failed to build with j-oem-6.1.0-1018.18 (LP: #2028932)
    - SAUCE: Revert "libbpf: fix offsetof() and container_of() to work with CO-RE"

  [ Ubuntu: 6.5.0-2.2 ]

  * mantic/linux: 6.5.0-2.2 -proposed tracker (LP: #2033240)
  * Soundwire support for Dell SKU0C87 devices (LP: #2029281)
    - SAUCE: ASoC: Intel: soc-acpi: add support for Dell SKU0C87 devices
  * Fix numerous AER related issues (LP: #2033025)
    - SAUCE: PCI/AER: Disable AER service during suspend, again
    - SAUCE: PCI/DPC: Disable DPC service during suspend, again
  * Support Realtek RTL8852CE WiFi 6E/BT Combo (LP: #2025672)
    - wifi: rtw89: debug: Fix error handling in rtw89_debug_priv_btc_manual_set()
    - Bluetooth: btrtl: Load FW v2 otherwise FW v1 for RTL8852C
  * Rebase to v6.5

  [ Ubuntu: 6.5.0-1.1 ]

  * mantic/linux: 6.5.0-1.1 -proposed tracker (LP: #2032750)
  * Packaging resync (LP: #1786013)
    - [Packaging] resync update-dkms-versions helper
    - [Packaging] update variants
    - debian/dkms-versions -- update from kernel-versions (main/d2023.07.26)
  * ceph: support idmapped mounts (LP: #2032959)
    - SAUCE: libceph: add spinlock around osd->o_requests
    - SAUCE: libceph: define struct ceph_sparse_extent and add some helpers
    - SAUCE: libceph: new sparse_read op, support sparse reads on msgr2 crc
      codepath
    - SAUCE: libceph: support sparse reads on msgr2 secure codepath
    - SAUCE: libceph: add sparse read support to msgr1
    - SAUCE: libceph: add sparse read support to OSD client
    - SAUCE: ceph: add new mount option to enable sparse reads
    - SAUCE: ceph: preallocate inode for ops that may create one
    - SAUCE: ceph: make ceph_msdc_build_path use ref-walk
    - SAUCE: libceph: add new iov_iter-based ceph_msg_data_type and
      ceph_osd_data_type
    - SAUCE: ceph: use osd_req_op_extent_...

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 6.5.0-5.5

---------------
linux (6.5.0-5.5) mantic; urgency=medium

  * mantic/linux: 6.5.0-5.5 -proposed tracker (LP: #2034546)

  * Packaging resync (LP: #1786013)
    - [Packaging] update helper scripts
    - debian/dkms-versions -- update from kernel-versions (main/d2023.08.23)

 -- Andrea Righi <email address hidden> Wed, 06 Sep 2023 15:51:04 +0200