[Bug 1954676] Re: jammy 5.15 kernel soft lockup when zfs.ko is loaded on s390x w/ gcc >= 11.2.0-10ubuntu1 / gcc-11 PLT regression on s390x

[Dimitri John Ledkov]

** Changed in: gcc-11 (Ubuntu Impish)
       Status: New => Invalid

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Title:
  jammy 5.15 kernel soft lockup when zfs.ko is loaded on s390x w/ gcc >=
  11.2.0-10ubuntu1 / gcc-11 PLT regression on s390x

Status in Ubuntu on IBM z Systems:
  Fix Released
Status in gcc-11 package in Ubuntu:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in gcc-11 source package in Impish:
  Invalid
Status in linux source package in Impish:
  Fix Released
Status in gcc-11 source package in Jammy:
  Fix Released
Status in linux source package in Jammy:
  Fix Released

Bug description:
  [Impact]

  Installing zfs-dkms seems to trigger a soft lockup issue as soon as
  zfs.ko is loaded. When the soft lockup happens the system isn't
  reachable anymore via ssh and on the console we can see some exlicit
  rcu stall warnings.

  This seems to happen only when zfs is compile with gcc >=
  11.2.0-10ubuntu1. Downgrading gcc to previous versions doesn't show
  the problem and zfs is working just fine.

  [Test case]

  On s390x install the latest 5.15 Jammy kernel and run:
  apt install zfs-dkms

  [Fix]

  Temporary workaround is to build zfs with gcc-10 on s390x.

  [Regression potential]

  Building a kernel module with a different compiler is never 100% safe,
  we may experience potential crashes / panics if the ABI is not
  compatible. Moreover, if we build zfs with gcc-10 we are going to lose
  some of the performance benefits provided by gcc-11.

  However these regressions are limited to zfs on s390x and without this
  change zfs is broken anyway on this architecture.

  [Further analysis]

  @IBM

  Issue report to zfs upstream at
  https://github.com/openzfs/zfs/issues/12942

  Reverting
  https://gcc.gnu.org/git/?p=gcc.git;a=patch;h=2335aa8771acd06b082d3e15d9f21ae0a802afd7
  appears to make everything work, the compiled kernel and zfs.ko are
  loadable/unloadable once again.

  Please bring this issue to the attention of  Ilya Leoshkevich

  Potentially this means we may have missbuilt userspace binaries in the
  archive for s390x.

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