On Sat, 31 Jul 2021, Christophe Leroy wrote:

quoted

Stan Johnson contacted me about a regression in mainline that he 
observed on his G3 Powerbooks. Using 'git bisect' we determined that 
this patch was the cause of the regression, i.e. commit 4c0104a83fc3 
("powerpc/32: Dismantle EXC_XFER_STD/LITE/TEMPLATE").

When testing 4c0104a83fc and all subsequent builds, various user 
processes were liable to segfault. Here is the console log that Stan 
provided:

Hi, i will be able to look at that more in details next week, however I 
have a few preliminary qurstions.

Can you reliabily reproduce the problem with the said commit, and can 
you reliabily run without problem with the parent commit ? 

Yes and yes. (I already asked Stan to establish those things before I 
contacted the list.)

I'm asking because at first look that commit doesn't bring any 
functionnal change.

Coukd you provide your .config ?

Please see attached. My understanding is that all of Stan's builds were 
performed like this:

$ cp ../dot-config-powermac-5.13 .config
$ make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- -j4 clean olddefconfig vmlinux

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