cpu hot-remove fails with nvme device

[AceLan Kao]

Using cpu hotplug to disable (offline) a cpu:
echo 0 > /sys/devices/system/cpu/cpu10/online
does not return.

Machine is usable, and cpu10 is marked as offline, but any test
scripts hangs because the "echo 0" never returned.

Doing bisect pointed to this commit id: a4aea5623d "NVMe: Convert to blk-mq"
Indeed, the test machine in question has an NVMe card.
Doing "rmmod nvme" and then disabling cpus works.

[Luis Henriques (henrix)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-vivid' to 'verification-done-vivid'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[AceLan Kao (acelankao)]

This issue has been fix by kernel 3.19.0-31.36

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 3.19.0-31.36

---------------
linux (3.19.0-31.36) vivid; urgency=low

  [ Luis Henriques ]

  * Release Tracking Bug
    - LP: #1503703

  [ Andy Whitcroft ]

  * Revert "SAUCE: aufs3: mmap: Fix races in madvise_remove() and
    sys_msync()"
    - LP: #1503655

  [ Ben Hutchings ]

  * SAUCE: aufs3: mmap: Fix races in madvise_remove() and sys_msync()
    - LP: #1503655
    - CVE-2015-7312

linux (3.19.0-31.35) vivid; urgency=low

  [ Brad Figg ]

  * Release Tracking Bug
    - LP: #1503005

  [ Ben Hutchings ]

  * SAUCE: aufs3: mmap: Fix races in madvise_remove() and sys_msync()
    - CVE-2015-7312

  [ Craig Magina ]

  * [Config] Add XGENE_EDAC, EDAC_SUPPORT and EDAC_ATOMIC_SCRUB
    - LP: #1494357

  [ John Johansen ]

  * SAUCE: (no-up) apparmor: fix mount not handling disconnected paths
    - LP: #1496430

  [ Laurent Dufour ]

  * SAUCE: powerpc/hvsi: Fix endianness issues in the HVSI driver
    - LP: #1499357

  [ Tim Gardner ]

  * [Config] CONFIG_RTC_DRV_XGENE=y for only arm64
    - LP: #1499869

  [ Upstream Kernel Changes ]

  * Revert "sit: Add gro callbacks to sit_offload"
    - LP: #1500493
  * ipmi/powernv: Fix minor locking bug
    - LP: #1493017
  * mmc: sdhci-pci: set the clear transfer mode register quirk for O2Micro
    - LP: #1472843
  * perf probe ppc: Fix symbol fixup issues due to ELF type
    - LP: #1485528
  * perf probe ppc: Use the right prefix when ignoring SyS symbols on ppc
    - LP: #1485528
  * perf probe ppc: Enable matching against dot symbols automatically
    - LP: #1485528
  * perf probe ppc64le: Fix ppc64 ABIv2 symbol decoding
    - LP: #1485528
  * perf probe ppc64le: Prefer symbol table lookup over DWARF
    - LP: #1485528
  * perf probe ppc64le: Fixup function entry if using kallsyms lookup
    - LP: #1485528
  * perf probe: Improve detection of file/function name in the probe
    pattern
    - LP: #1485528
  * perf probe: Ignore tail calls to probed functions
    - LP: #1485528
  * seccomp: cap SECCOMP_RET_ERRNO data to MAX_ERRNO
    - LP: #1496073
  * EDAC: Cleanup atomic_scrub mess
    - LP: #1494357
  * arm64: Enable EDAC on ARM64
    - LP: #1494357
  * MAINTAINERS: Add entry for APM X-Gene SoC EDAC driver
    - LP: #1494357
  * Documentation: Add documentation for the APM X-Gene SoC EDAC DTS
    binding
    - LP: #1494357
  * EDAC: Add APM X-Gene SoC EDAC driver
    - LP: #1494357
  * arm64: Add APM X-Gene SoC EDAC DTS entries
    - LP: #1494357
  * EDAC, edac_stub: Drop arch-specific include
    - LP: #1494357
  * NVMe: Fix blk-mq hot cpu notification
    - LP: #1498778
  * blk-mq: Shared tag enhancements
    - LP: #1498778
  * blk-mq: avoid access hctx->tags->cpumask before allocation
    - LP: #1498778
  * x86/ldt: Make modify_ldt synchronous
    - LP: #1500493
  * x86/ldt: Correct LDT access in single stepping logic
    - LP: #1500493
  * x86/ldt: Correct FPU emulation access to LDT
    - LP: #1500493
  * md: flush ->event_work before stopping array.
    - LP: #1500493
  * ipv6: addrconf: validate new MTU before applying it
    - LP: #1500493
  * virtio-net: drop NETIF_F_FRAGLIST
    - LP: #1500493
  * RDS: verify the underlying transport exists bef...