linux-kernel - Re: [PATCH v3] bitfield.h: add FIELD_MAX() and field

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Date:   Wed, 1 Apr 2020 12:54:43 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Alex Elder <elder@...aro.org>
Cc:     Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Johannes Berg <johannes@...solutions.net>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v3] bitfield.h: add FIELD_MAX() and field_max()

On Wed, Apr 1, 2020 at 12:44 PM Alex Elder <elder@...aro.org> wrote:
>
> On 4/1/20 2:13 PM, Nick Desaulniers wrote:
> > On Wed, Apr 1, 2020 at 11:24 AM Alex Elder <elder@...aro.org> wrote:
> >>
> >> On 4/1/20 12:35 PM, Nick Desaulniers wrote:
> >>>> Define FIELD_MAX(), which supplies the maximum value that can be
> >>>> represented by a field value.  Define field_max() as well, to go
> >>>> along with the lower-case forms of the field mask functions.
> >>>>
> >>>> Signed-off-by: Alex Elder <elder@...aro.org>
> >>>> Acked-by: Jakub Kicinski <kuba@...nel.org>
> >>>> ---
> >>>> v3: Rebased on latest netdev-next/master.
> >>>>
> >>>> David, please take this into net-next as soon as possible.  When the
> >>>> IPA code was merged the other day this prerequisite patch was not
> >>>> included, and as a result the IPA driver fails to build.  Thank you.
> >>>>
> >>>>   See: https://lkml.org/lkml/2020/3/10/1839
> >>>>
> >>>>                                      -Alex
> >>>
> >>> In particular, this seems to now have regressed into mainline for the 5.7
> >>> merge window as reported by Linaro's ToolChain Working Group's CI.
> >>> Link: https://github.com/ClangBuiltLinux/linux/issues/963
> >>
> >> Is the problem you're referring to the result of a build done
> >> in the midst of a bisect?
> >>
> >> The fix for this build error is currently present in the
> >> torvalds/linux.git master branch:
> >>     6fcd42242ebc soc: qcom: ipa: kill IPA_RX_BUFFER_ORDER
> >
> > Is that right? That patch is in mainline, but looks unrelated to what
> > I'm referring to.
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6fcd42242ebcc98ebf1a9a03f5e8cb646277fd78
> > From my github link above, the issue I'm referring to is a
> > -Wimplicit-function-declaration warning related to field_max.
> > 6fcd42242ebc doesn't look related.
>
> I'm very sorry, I pointed you at the wrong commit.  This one is
> also present in torvalds/linux.git master:
>
>   e31a50162feb bitfield.h: add FIELD_MAX() and field_max()
>
> It defines field_max() as a macro in <linux/bitfield.h>, and
> "gsi.c" includes that header file.
>
> This was another commit that got added late, after the initial
> IPA code was accepted.

Yep, that looks better.

>
> >> I may be mistaken, but I believe this is the same problem I discussed
> >> with Maxim Kuvyrkov this morning.  A different build problem led to
> >> an automated bisect, which conluded this was the cause because it
> >> landed somewhere between the initial pull of the IPA code and the fix
> >> I reference above.
> >
> > Yes, Maxim runs Linaro's ToolChain Working Group (IIUC, but you work
> > there, so you probably know better than I do), that's the CI I was
> > referring to.
> >
> > I'm more concerned when I see reports of regressions *in mainline*.
> > The whole point of -next is that warnings reported there get fixed
> > BEFORE the merge window opens, so that we don't regress mainline.  Or
> > we drop the patches in -next.
>
> Can you tell me where I can find the commit id of the kernel
> that is being built when this error is reported?  I would
> like to examine things and build it myself so I can fix it.
> But so far haven't found what I need to check out.

>From the report: https://groups.google.com/g/clang-built-linux/c/pX-kr_t5l_A
Configuration details:
rr[llvm_url]="https://github.com/llvm/llvm-project.git"
rr[linux_url]="https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git"
rr[linux_branch]="7111951b8d4973bda27ff663f2cf18b663d15b48"

the linux_branch looks like a SHA of what the latest ToT of mainline
was when the CI ran.

I was suspecting that maybe there was a small window between the
regression, and the fix, and when the bot happened to sync.  But it
seems that: e31a50162feb352147d3fc87b9e036703c8f2636 landed before
7111951b8d4973bda27ff663f2cf18b663d15b48 IIUC.

So I think the bot had your change when it ran, so still seeing a
failure is curious.  Unless I've misunderstood something.
-- 
Thanks,
~Nick Desaulniers