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[Bug 1589910] Re: [regression trusty] oops/sig 4: power7_enter_nap_mode+0x0/0x18


** Patch added: "0001-powerpc-powernv-Fix-incomplete-backport-of-8117ac6.patch"

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  [regression trusty] oops/sig 4: power7_enter_nap_mode+0x0/0x18

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Trusty:
  In Progress

Bug description:
  Arch: ppc64el
  Release: Trusty/14.04

  [ 0.194023] Oops: Exception in kernel mode, sig: 4 [#3]
  [ 0.194128] SMP NR_CPUS=2048 NUMA PowerNV
  [ 0.194225] Modules linked in:
  [ 0.194316] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G D 3.13.0-48-generic #80-Ubuntu
  [ 0.194403] task: c0000007f26957c0 ti: c0000007f2728000 task.ti: c0000007f2728000
  [ 0.194477] NIP: c000000001598930 LR: c00000000001897c CTR: c00000000002abfc
  [ 0.194551] REGS: c0000007f272b800 TRAP: 0e40 Tainted: G D (3.13.0-48-generic)
  [ 0.194651] MSR: 9000000000081001 <SF,HV,ME,LE> CR: 22004088 XER: 00000000
  [ 0.194788] CFAR: c00000000002ace4 SOFTE: 0
  [ 0.195869] NIP [c000000001598930] power7_enter_nap_mode+0x0/0x18

  SRU Justification:

  = Impact =
  Since kernel 3.13.0-46 there was a incorrect backport of a stable patch which causes several oops messages and ends with an automatic reboot. Which renders all kernels since then to be unbootable on ppc64el. This happens because instead of the function address to power7_enter_nap_mode, the change accidentally loads the address of a related symbol table.

  = Fix =
  Pick up the alternate declaration of the function label as it is in the original upstream change (commmit 8117ac6 powerpc/powernv: Switch off MMU before entering nap/sleep/rvwinkle mode). In 3.13 this requires one more change because there is one call site that refers to a label name which would be implicitly generated by the macro that gets replaced. This was done upstream, too, in (b1576fe powerpc: No need to use dot symbols when branching to a function).

  = Testcase =
  Trying to boot current Trusty kernels on a Power8 host fails all the time. With the change applied the host comes up without errors.

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