On Sun, 1 Aug 2021, Stan Johnson wrote:

quoted

quoted

Could you try without CONFIG_VMAP_STACK

Stan, would you please test the following build:

$ git checkout v5.13
$ cp ../dot-config-powermac-5.13 .config
$ scripts/config -d CONFIG_VMAP_STACK
$ make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- -j4 clean olddefconfig vmlinux

Please see the attached serial console log (four boots):
1) v5.13-mac, CONFIG_VMAP_STACK=y, mem=512M (fails)
2) v5.13-mac, CONFIG_VMAP_STACK=y, mem=384M (works)
3) v5.13-mac, CONFIG_VMAP_STACK=n, mem=512M (works)
4) v5.13-mac, CONFIG_VMAP_STACK=n, mem=384M (works)

My apologies if the extra boots were not needed (due to the time
difference, I'm trying to anticipate future requests).

Cutting and pasting Finn's commands above builds a new kernel
(5.13.0-pmac) with the following in .config:

$ fgrep VMAP .config
CONFIG_HAVE_ARCH_VMAP_STACK=y
CONFIG_VMAP_STACK=y

That's odd. It works correctly here:

$ cp ../dot-config-powermac-5.13 .config
$ grep CONFIG_VMAP_STACK .config
CONFIG_VMAP_STACK=y
$ scripts/config -d CONFIG_VMAP_STACK
$ grep CONFIG_VMAP_STACK .config
# CONFIG_VMAP_STACK is not set

Anyway, I see that you resolved the problem:

...

$ fgrep VMAP .config
CONFIG_HAVE_ARCH_VMAP_STACK=y
# CONFIG_VMAP_STACK is not set

3) Same as 1 (512M) but with CONFIG_VMAP_STACK not set in v5.13.
Everything works (no problems with X, no errors logged).

4) Same as 2 (384M) but with CONFIG_VMAP_STACK not set in v5.13.
Everything works (no problems with X, no errors logged).

Thanks for collecting those results.

It appears that Christophe was right. Disabling CONFIG_VMAP_STACK avoids 
the crashes in v5.13. (Enabling CONFIG_VMAP_STACK worked fine in v5.12.)