linux-kernel - Re: [PATCH v3 31/41] powerpc/32: Dismantle EXC_XFER

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Date:   Mon, 2 Aug 2021 09:48:36 +1000 (AEST)
From:   Finn Thain <fthain@...ux-m68k.org>
To:     Stan Johnson <userm57@...oo.com>
cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Nick Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v3 31/41] powerpc/32: Dismantle
 EXC_XFER_STD/LITE/TEMPLATE

On Sun, 1 Aug 2021, Stan Johnson wrote:

> > 
> >> 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.)