This bug was fixed in the package linux - 4.4.0-6.21

---------------
linux (4.4.0-6.21) xenial; urgency=low

  [ Tim Gardner ]

  * Release Tracking Bug
    - LP: #1546283

  *  Naples/Zen, NTB Driver  (LP: #1542071)
    - [Config] CONFIG_NTB_AMD=m
    - NTB: Add support for AMD PCI-Express Non-Transparent Bridge

  * [Hyper-V] kernel panic occurs when installing Ubuntu Server x32 (LP: #1495983)
    - SAUCE: storvsc: use small sg_tablesize on x86

  * Enable arm64 emulation of removed ARMv7 instructions (LP: #1545542)
    - [Config] CONFIG_ARMV8_DEPRECATED=y

  * Surelock-GA2:kernel panic/ exception @ pcibios_set_pcie_reset_state+0x118/0x280 + cxl_reset+0x5c/0xc0 (LP: #1545037)
    - powerpc/eeh: Fix stale cached primary bus

  * Miscellaneous Ubuntu changes
    - SAUCE: fs: Add user namesapace member to struct super_block
    - SAUCE: fs: Limit file caps to the user namespace of the super block
    - SAUCE: Smack: Add support for unprivileged mounts from user namespaces
    - SAUCE: block_dev: Support checking inode permissions in lookup_bdev()
    - SAUCE: block_dev: Check permissions towards block device inode when mounting
    - SAUCE: fs: Treat foreign mounts as nosuid
    - SAUCE: selinux: Add support for unprivileged mounts from user namespaces
    - SAUCE: userns: Replace in_userns with current_in_userns
    - SAUCE: Smack: Handle labels consistently in untrusted mounts
    - SAUCE: fs: Check for invalid i_uid in may_follow_link()
    - SAUCE: cred: Reject inodes with invalid ids in set_create_file_as()
    - SAUCE: fs: Refuse uid/gid changes which don't map into s_user_ns
    - SAUCE: fs: Update posix_acl support to handle user namespace mounts
    - SAUCE: fs: Ensure the mounter of a filesystem is privileged towards its inodes
    - SAUCE: fs: Don't remove suid for CAP_FSETID in s_user_ns
    - SAUCE: fs: Allow superblock owner to access do_remount_sb()
    - SAUCE: capabilities: Allow privileged user in s_user_ns to set security.* xattrs
    - SAUCE: fuse: Add support for pid namespaces
    - SAUCE: fuse: Support fuse filesystems outside of init_user_ns
    - SAUCE: fuse: Restrict allow_other to the superblock's namespace or a descendant
    - SAUCE: fuse: Allow user namespace mounts
    - SAUCE: mtd: Check permissions towards mtd block device inode when mounting
    - SAUCE: fs: Update i_[ug]id_(read|write) to translate relative to s_user_ns
    - SAUCE: quota: Convert ids relative to s_user_ns
    - SAUCE: evm: Translate user/group ids relative to s_user_ns when computing HMAC
    - SAUCE: fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems
    - SAUCE: quota: Treat superblock owner as privilged
    - SAUCE: ima/evm: Allow root in s_user_ns to set xattrs
    - SAUCE: block_dev: Forbid unprivileged mounting when device is opened for writing
    - SAUCE: ext4: Add support for unprivileged mounts from user namespaces
    - SAUCE: ext4: Add module parameter to enable user namespace mounts
    - SAUCE: fuse: Add module parameter to enable user namespace mounts

  * Miscellaneous upstream changes
    - megaraid: Fix possible NULL pointer deference in mraid_mm_ioctl
    - libahci: Implement the capability to override the generic ahci interrupt handler.
    - ata: Remove the AHCI_HFLAG_EDGE_IRQ support from libahci.
    - ahci_xgene: Implement the workaround to fix the missing of the edge interrupt for the HOST_IRQ_STAT.

 -- Tim Gardner <email address hidden>  Fri, 12 Feb 2016 09:49:05 -0700