linux-kernel - Re: [PATCH v2] srcu: avoid escaped section names

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Date:   Wed, 7 Oct 2020 14:05:03 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Sedat Dilek <sedat.dilek@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, rcu@...r.kernel.org,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2] srcu: avoid escaped section names

On Mon, Oct 05, 2020 at 11:56:23PM -0700, Nathan Chancellor wrote:
> On Mon, Oct 05, 2020 at 11:49:10AM -0700, Paul E. McKenney wrote:
> > On Mon, Oct 05, 2020 at 08:38:42PM +0200, Sedat Dilek wrote:
> > > On Mon, Oct 5, 2020 at 8:29 PM 'Nick Desaulniers' via Clang Built
> > > Linux <clang-built-linux@...glegroups.com> wrote:
> > > >
> > > > On Fri, Oct 2, 2020 at 1:51 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> > > > >
> > > > > On Wed, Sep 30, 2020 at 01:55:48PM -0700, Nick Desaulniers wrote:
> > > > > > On Wed, Sep 30, 2020 at 1:40 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> > > > > > >
> > > > > > > On Tue, Sep 29, 2020 at 12:25:49PM -0700, Nick Desaulniers wrote:
> > > > > > > > The stringification operator, `#`, in the preprocessor escapes strings.
> > > > > > > > For example, `# "foo"` becomes `"\"foo\""`.  GCC and Clang differ in how
> > > > > > > > they treat section names that contain \".
> > > > > > > >
> > > > > > > > The portable solution is to not use a string literal with the
> > > > > > > > preprocessor stringification operator.
> > > > > > > >
> > > > > > > > Link: https://bugs.llvm.org/show_bug.cgi?id=42950
> > > > > > > > Fixes: commit fe15b50cdeee ("srcu: Allocate per-CPU data for DEFINE_SRCU() in modules")
> > > > > > > > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > > > > > >
> > > > > > > I am guessing that this needs to go up with other patches.  If so:
> > > > > > >
> > > > > > > Acked-by: Paul E. McKenney <paulmck@...nel.org>
> > > > > > >
> > > > > > > If not, let me know and I will queue it.
> > > > > >
> > > > > > I could have bundled them up as a series.  I think you can pick it up,
> > > > > > and I'll owe you a beer?
> > > > >
> > > > > It is queued, thank you!
> > > > >
> > > > > When does it need to hit mainline?  (Your default is the v5.11 merge
> > > > > window, that is, the one following the upcoming merge window.)
> > > >
> > > > No rush, this patch wasn't blocking any known issue, just a cleanup
> > > > while I was in the neighborhood.  100 years ago, I was an Eagle scout.
> > > > Pretty sure there was a motto about "leaving things better than you
> > > > found them."  Thanks for help resolving the merge conflict reported in
> > > > -next related to it.
> > > 
> > > Wasn't there a problem with your "Fixes:" tag (Fixes: *drop word
> > > "commit"* commit_hashid ("...")?
> > 
> > Indeed there was, and I have it noted to be fixed on my next rebase.
> > 
> > Perhaps another reason not to rush to mainline though.  ;-)
> > 
> > 							Thanx, Paul
> 
> I am replying here as well so that the relevant parties are in the know
> but I believe this patch should be fast tracked with a cc stable tag as
> this appears to be the root cause of the issue that Nick reported a few
> weeks ago:
> 
> https://lore.kernel.org/rcu/CAKwvOdm4AQhobdkKT08bjPGb15N58QN79XWxEaQt-P5Dk4+avQ@mail.gmail.com/
> https://github.com/ClangBuiltLinux/linux/issues/1081
> 
> I can reproduce the issue on next-20201002 on my Raspberry Pi 4 just by
> booting it up. As soon as I apply this patch, all warnings disappear. I
> asked the original reporters to test if the patch resolves the issue for
> them but I figured more visibility on this, the sooner. The commit
> message might need to be revised if this turns out to be the case to
> make it more apparent that it has a user visible issue, rather than just
> a QoL fix.
> 
> Additionally, it seems like the patch is missing some reviewed by tags
> from Kees, Sedat, and myself. Feel free to add a
> 
> Tested-by: Nathan Chancellor <natechancellor@...il.com>
> 
> as well.

Good catch, and apologies to all concerned!  I have removed the stray
"commit" and, based posts earlier in this thread, I have also added:

Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>
Reviewed-by: Sedat Dilek <sedat.dilek@...il.com>

Thank you all!

							Thanx, Paul