linux-kernel - Re: [PATCH v2 2/2] kbuild: trace functions in subdirectories of lib/

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Date:   Wed, 22 Jul 2020 11:08:51 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Haren Myneni <haren@...ibm.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Tal Gilboa <talgi@...lanox.com>, kunit-dev@...glegroups.com,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, live-patching@...r.kernel.org
Subject: Re: [PATCH v2 2/2] kbuild: trace functions in subdirectories of lib/

On Wed, Jul 8, 2020 at 1:02 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue,  7 Jul 2020 18:21:17 +0900
> Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> >   ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
> >
> > exists here in sub-directories of lib/ to keep the behavior of
> > commit 2464a609ded0 ("ftrace: do not trace library functions").
> >
> > Since that commit, not only the objects in lib/ but also the ones in
> > the sub-directories are excluded from ftrace (although the commit
> > description did not explicitly mention this).
> >
> > However, most of library functions in sub-directories are not so hot.
> > Re-add them to ftrace.
>
> I'm OK with this change, but note, it wasn't just the hot path that I
> disabled ftrace on lib for, but some of these calls are done very early
> at boot up. It may have been PowerPC that I was stumbling over. The
> issue is that they would call mcount before the kernel was mapped
> properly, and the system would crash.
>
> My PowerPC box no longer boots so I can't test this anymore. But a lot
> has changed since 2008, and all this may very well be OK.
>
> -- Steve


That's why I split this into two commits
so that we can do git-bisect and
revert the second one in case of a regression.

Anyway, we have some more time to test this in linux-next
(and somebody reports an issue, if any).


-- 
Best Regards
Masahiro Yamada