linux-kernel - Re: [PATCH 5.16 00/28] 5.16.2-rc1 review

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Date:   Wed, 19 Jan 2022 07:55:55 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        NeilBrown <neilb@...e.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, patches@...nelci.org,
        lkft-triage@...ts.linaro.org, Pavel Machek <pavel@...x.de>,
        Jon Hunter <jonathanh@...dia.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        stable <stable@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 5.16 00/28] 5.16.2-rc1 review

On 1/18/22 11:53 PM, Linus Torvalds wrote:
> On Wed, Jan 19, 2022 at 9:30 AM Naresh Kamboju
> <naresh.kamboju@...aro.org> wrote:
>>
>> Inconsistent kallsyms data
> 
> This tends to be a "odd build environment" problem, and very very
> random. Triggered by very particular compiler versions and just some
> odd code modement details.
> 

It happens once in a while depending on the compiler version and
on how symbols are arranged, and new compiler specific symbols showing up.
I had submitted a patch a while ago that kept retrying a few more times
before giving up (that was rejected). We carry a patch in ChromeOS kernels
which tells us what the offending symbols are in case we see the problem
in our builds.

> I'd suggest doing a completely clean build and disabling ccache, and
> seeing if that makes it go away.
> 

My experience is that once it starts, it will show up randomly and become
more and more prevalent over time until almost all builds fail. powerpc
seems to be affected a lot by this problem, but we have also seen it
on x86. When that happens, someone has to go in and figure out the
offending symbol(s) and add it or them to some exception list.

Guenter