Rahul Rameshbabu [off-list ref] writes:

On Fri, 15 Dec, 2023 23:44:49 +1100 Michael Ellerman [off-list ref] wrote:

quoted

There are reports of kernels crashing due to stack overflow while
running OpenShift (Kubernetes). The primary contributor to the stack
usage seems to be openvswitch, which is used by OVN-Kubernetes (based on
OVN (Open Virtual Network)), but NFS also contributes in some stack
traces.

There may be some opportunities to reduce stack usage in the openvswitch
code, but doing so potentially require tradeoffs vs performance, and
also requires testing across architectures.

Looking at stack usage across the kernel (using -fstack-usage), shows
that ppc64le stack frames are on average 50-100% larger than the
equivalent function built for x86-64. Which is not surprising given the
minimum stack frame size is 32 bytes on ppc64le vs 16 bytes on x86-64.

So increase the default stack size to 32KB for the modern 64-bit Book3S
platforms, ie. pseries (virtualised) and powernv (bare metal). That
leaves the older systems like G5s, and the AmigaOne (pasemi) with a 16KB
stack which should be sufficient on those machines.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---

We noticed this change is causing assembler issues for us when building
the kernel.

  make ARCH=powerpc KERNELRELEASE=6.8.0-rc2_for_upstream_debug_2024_02_06_20_01 KBUILD_BUILD_VERSION=1
  arch/powerpc/kernel/switch.S: Assembler messages:
  arch/powerpc/kernel/switch.S:249: Error: operand out of range (0x000000000000fe50 is not between 0xffffffffffff8000 and 0x0000000000007fff)
  make[6]: *** [scripts/Makefile.build:361: arch/powerpc/kernel/switch.o] Error 1
  make[5]: *** [scripts/Makefile.build:481: arch/powerpc/kernel] Error 2
  make[5]: *** Waiting for unfinished jobs....
  make[4]: *** [scripts/Makefile.build:481: arch/powerpc] Error 2
  make[4]: *** Waiting for unfinished jobs....
  make[3]: *** [Makefile:1921: .] Error 2

There's a fix in my fixes branch:
  https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?h=fixes&id=f1acb109505d983779bbb7e20a1ee6244d2b5736

I'll send it to Linus this week.

cheers