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

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Message-ID: <1d601b7c-1e39-e372-39a5-e1e98e56e2a5@linux-m68k.org>
Date:   Sun, 1 Aug 2021 11:21:23 +1000 (AEST)
From:   Finn Thain <fthain@...ux-m68k.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
cc:     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>,
        Stan Johnson <userm57@...oo.com>
Subject: Re: [PATCH v3 31/41] powerpc/32: Dismantle
 EXC_XFER_STD/LITE/TEMPLATE

On Sat, 31 Jul 2021, Christophe Leroy wrote:

> > 
> > 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
View attachment "dot-config-powermac-5.13" of type "text/plain" (90679 bytes)