** Changed in: gcc-11 (Ubuntu Jammy)
Status: New => Confirmed
** Changed in: ubuntu-z-systems
Status: New => Confirmed
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https://bugs.launchpad.net/bugs/1954676
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:
Confirmed
Status in gcc-11 package in Ubuntu:
Confirmed
Status in zfs-linux package in Ubuntu:
New
Status in gcc-11 source package in Jammy:
Confirmed
Status in zfs-linux source package in Jammy:
New
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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