CONFIG_LATENCYTOP should be disabled

[Tim Gardner]

SRU Justification

[Impact]

There were some recent changes on the main kernels to fix some syntax issues with the annotations files (Propagate "Update annotations and fix errors" to all derivatives), after I replicated the changes from bionic/linux to bionic/linux-raspi2 I started getting this enforcement error:

check-config: FAIL (y != n): CONFIG_LATENCYTOP policy<{'amd64-generic': 'n', 'amd64-lowlatency': 'y', 'arm64': 'n', 'armhf': 'n', 'i386': 'n', 'ppc64el': 'n', 's390x': 'n'}> mark<ENFORCED> note<https://lists.ubuntu.com/archives/kernel-team/2014-July/045006.html, LP#1655986>
It seems we were supposed to have the same enforcement as the main kernel (= n) but the raspi2 config has it actually enabled.

Looking at the url and the bug reference on the enforcement notes, it seems it doesn't make much sense to keep it enabled for non-lowlatency kernels.

@juerghaefliger confirmed we should disable this option:

Yes, it should be disabled. I did the same for hirsute earlier this year after Seth fixed the master config annotations:
~ubuntu-kernel/ubuntu/+source/linux-raspi/+git/hirsute - [no description]

If I remember correctly I made some other config changes due to Seth's
changes.

[Test Plan]

Install latencytop, try to run the tool.

[Where problems could occur]

Disabling this config removes information that userspace might depend on.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1928394

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-raspi2 - 4.15.0-1086.91

---------------
linux-raspi2 (4.15.0-1086.91) bionic; urgency=medium

  * bionic/linux-raspi2: 4.15.0-1086.91 -proposed tracker (LP: #1927644)

  * CONFIG_LATENCYTOP should be disabled (LP: #1928394)
    - [Config] raspi2: CONFIG_LATENCYTOP=n

  [ Ubuntu: 4.15.0-144.148 ]

  * bionic/linux: 4.15.0-144.148 -proposed tracker (LP: #1927648)
  * Introduce the 465 driver series, fabric-manager, and libnvidia-nscq
    (LP: #1925522)
    - debian/dkms-versions -- add NVIDIA 465 and migrate 450 to 460
  * xfrm_policy.sh / pmtu.sh / udpgso_bench.sh from net in
    ubuntu_kernel_selftests will fail if running the whole suite (LP: #1856010)
    - selftests/net: bump timeout to 5 minutes
  * locking/qrwlock: Fix ordering in queued_write_lock_slowpath() (LP: #1926184)
    - locking/barriers: Introduce smp_cond_load_relaxed() and
      atomic_cond_read_relaxed()
    - locking/qrwlock: Fix ordering in queued_write_lock_slowpath()
  * Bionic update: upstream stable patchset 2021-04-30 (LP: #1926808)
    - net: fec: ptp: avoid register access when ipg clock is disabled
    - powerpc/4xx: Fix build errors from mfdcr()
    - atm: eni: dont release is never initialized
    - atm: lanai: dont run lanai_dev_close if not open
    - Revert "r8152: adjust the settings about MAC clock speed down for RTL8153"
    - ixgbe: Fix memleak in ixgbe_configure_clsu32
    - net: tehuti: fix error return code in bdx_probe()
    - sun/niu: fix wrong RXMAC_BC_FRM_CNT_COUNT count
    - gpiolib: acpi: Add missing IRQF_ONESHOT
    - nfs: fix PNFS_FLEXFILE_LAYOUT Kconfig default
    - NFS: Correct size calculation for create reply length
    - net: hisilicon: hns: fix error return code of hns_nic_clear_all_rx_fetch()
    - net: wan: fix error return code of uhdlc_init()
    - atm: uPD98402: fix incorrect allocation
    - atm: idt77252: fix null-ptr-dereference
    - sparc64: Fix opcode filtering in handling of no fault loads
    - u64_stats,lockdep: Fix u64_stats_init() vs lockdep
    - drm/radeon: fix AGP dependency
    - nfs: we don't support removing system.nfs4_acl
    - ia64: fix ia64_syscall_get_set_arguments() for break-based syscalls
    - ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign
    - squashfs: fix inode lookup sanity checks
    - squashfs: fix xattr id and id lookup sanity checks
    - arm64: dts: ls1046a: mark crypto engine dma coherent
    - arm64: dts: ls1012a: mark crypto engine dma coherent
    - arm64: dts: ls1043a: mark crypto engine dma coherent
    - ARM: dts: at91-sama5d27_som1: fix phy address to 7
    - dm ioctl: fix out of bounds array access when no devices
    - bus: omap_l3_noc: mark l3 irqs as IRQF_NO_THREAD
    - libbpf: Fix INSTALL flag order
    - macvlan: macvlan_count_rx() needs to be aware of preemption
    - net: dsa: bcm_sf2: Qualify phydev->dev_flags based on port
    - e1000e: add rtnl_lock() to e1000_reset_task
    - e1000e: Fix error handling in e1000_set_d0_lplu_state_82571
    - net/qlcnic: Fix a use after free in qlcnic_83xx_get_minidump_template
    - ftgmac100: Restart MAC HW once
    - can: peak_usb: add forgotten supported devices
    - can: c_can_pci: c_can_pci_remove...