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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Thu, 31 Jan 2019 11:06:15 +0100
Message-ID: <CACT4Y+Y5Y54iWn3w2jifjecDb+dZa_B=qZBsKTH8immHktij2Q@mail.gmail.com>
Subject: Re: [PATCH] kcov: convert kcov.refcount to refcount_t
To:     "Reshetova, Elena" <elena.reshetova@intel.com>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Anders Roxell <anders.roxell@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>
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On Thu, Jan 31, 2019 at 11:04 AM Reshetova, Elena
<elena.reshetova@intel.com> wrote:
>
>  > Just to check, has this been tested with CONFIG_REFCOUNT_FULL and
> > > something poking kcov?
> > >
> > > Given lib/refcount.c is instrumented, the refcount_*() calls will
> > > recurse back into the kcov code. It looks like that's fine, given these
> > > are only manipulated in setup/teardown paths, but it would be nice to be
> > > sure.
> >
> > A simple program using KCOV is available here:
> > https://elixir.bootlin.com/linux/v5.0-rc3/source/Documentation/dev-
> > tools/kcov.rst#L42
> > or here (it's like strace but collects and prints KCOV coverage):
> > https://github.com/google/syzkaller/blob/master/tools/kcovtrace/kcovtrace.c
> >
>
> Ok, so I finally got to compile kcov in and try the first test program
> and it works fine as far as I can see: runs, prints results, and no WARNs anywhere
> visible with regards to refcount_t.
>
> I did my test on 4.20 with CONFIG_REFCOUNT_FULL=y
> since I have serious issues getting 5.0 running as it is even from
> the stable branch, but unless kcov underwent some serious changes since December,
> it should not affect.

There were no changes that should affect this part.

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>


> Is it ok now for merging this change? The stricter mem ordering on dec_and_test
> hopefully will also lands soon.
>
> Best Regards,
> Elena.
>