linux-ext4 - Re: [GIT PULL] ext2, quota, and udf fixes for 6.6-rc1

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Message-ID: <ZTFh0NeYtvgcjSv8@smile.fi.intel.com>
Date:   Thu, 19 Oct 2023 20:05:20 +0300
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Ferry Toth <ftoth@...londelft.nl>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [GIT PULL] ext2, quota, and udf fixes for 6.6-rc1

On Thu, Oct 19, 2023 at 09:42:40AM -0700, Josh Poimboeuf wrote:
> On Thu, Oct 19, 2023 at 05:44:30PM +0300, Andy Shevchenko wrote:
> > So, what I have done so far.
> > 1) I have cleaned ccaches and stuff as I used it to avoid collisions;
> > 2) I have confirmed that CONFIG_DEBUG_LIST affects boot, the repo
> >    I'm using is published here [0][1];
> >    3) reverted quota patches until before this merge ([2] - last patch),
> >       still boots;
> > 4) reverted disabling of CONFIG_DEBUG_LIST [2], doesn't boot;
> > 5) okay, rebased on top of merge, i.e. 1500e7e0726e,  with DEBUG_LIST [3],
> > 	   doesn't boot;
> > 6) rebased [3] on one merge before, i.e. 63580f669d7f [4], voilà -- it boots!;
> > 
> > And (tadaam!) I have had an idea for a while to replace GCC with LLVM
> > (at least for this test), so [0] boots as well!
> > 
> > So, this merge triggered a bug in GCC, seems like... And it's _the_ merge
> > commit, which is so-o weird!
> 
> I'm not really a compiler person, but IMO it's highly unlikely to be a
> GCC bug unless you can point to the bad code generation.

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.

> If CONFIG_DEBUG_LIST is triggering it, it's most likely some kind of
> memory corruption, in which case seemingly random events can trigger the
> detection of it (or lack thereof).

Note disabling QUOTA has the same effect, so if it's a corruption it happens
somewhere there.

> Any chance it boots with the following?

Nope, no luck.

-- 
With Best Regards,
Andy Shevchenko