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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 19 Oct 2023 10:26:28 -0700
Message-ID: <CAHk-=wjXG52UNKCwwEU1A+QWHYfvKOieV0uFOpPkLR0NSvOjtg@mail.gmail.com>
Subject: Re: [GIT PULL] ext2, quota, and udf fixes for 6.6-rc1
To:     Andy Shevchenko <andriy.shevchenko@intel.com>
Cc:     Josh Poimboeuf <jpoimboe@kernel.org>, Jan Kara <jack@suse.cz>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Kees Cook <keescook@chromium.org>,
        Ferry Toth <ftoth@exalondelft.nl>,
        linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org
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On Thu, 19 Oct 2023 at 10:05, Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> Hmm... Then what's the difference between clang and GCC on the very same source
> code? One of them has a bug in my opinion.

Compiler bugs do happen, but they are quite rare (happily).

It's almost certainly just ambiguous code that happens to work with
one code generation, and not another.

It might be as simple as just hitting a timing bug, but considering
how consistent it is for you (with a particular config), it's more
likely to be something like an optimization that just happens to
trigger some subtle ordering requirement or other.

So then the "different compiler" is really just largely equivalent to
"different optimization options", and sometimes that causes problems.

That said, the quota dependency is quite odd, since normally I
wouldn't expect the quota code to really even trigger much during
boot. When it triggers that consistently, and that early during boot,
I would expect others to have reported more of this.

Strange.

                Linus