[PATCH 0/1] Fix ftrace oops/hang on RISC-V and ARM64

Colin King colin.king at canonical.com
Wed Oct 28 10:48:24 UTC 2020

From: Colin Ian King <colin.king at canonical.com>

== SRU Groovy ==

Running the ftrace self tests results in null pointer dereference oops
on RISC-V and also on ARM64.

== Fix ==

Upstream commit https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=4230e2deaa484b385aa01d598b2aea8e7f2660a6

== Testcase ==

Run the kernel ftrace selftest. Without the fix ftrace oopses on RISC-V
and ARM64 and can also hang on ARM64 too. With the fix, tests run
without oopsing or hanging.

== Regression Potential ==

This fix marks two functions as notrace, so the functionality of the
functions is not actually altered so the risk is negligible. If there
was a change in behaviour then RCU and stop machine operations will
break causing machine hangs. We don't observe this and RCU is used
heavily in the kernel so the code appears to not change the RCU
behaviour as expected.

The only change is the the functions are no longer traceable via
ftrace, which is the desired operation.

Zong Li (1):
  stop_machine, rcu: Mark functions as notrace

 kernel/rcu/tree.c     | 2 +-
 kernel/stop_machine.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)


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