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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 29 May 2023 07:00:05 -0400
Message-ID: <CAHk-=wh6sXSO63kka+EWEqq0tGwtOnXYFWMXPQ6T_wZa+Np3MQ@mail.gmail.com>
Subject: Re: [PATCH 2/2] module: add support to avoid duplicates early on load
To:     Johan Hovold <johan@kernel.org>
Cc:     Luis Chamberlain <mcgrof@kernel.org>,
        Lucas De Marchi <lucas.demarchi@intel.com>,
        Petr Pavlu <petr.pavlu@suse.com>, gregkh@linuxfoundation.org,
        rafael@kernel.org, song@kernel.org, lucas.de.marchi@gmail.com,
        christophe.leroy@csgroup.eu, peterz@infradead.org, rppt@kernel.org,
        dave@stgolabs.net, willy@infradead.org, vbabka@suse.cz,
        mhocko@suse.com, dave.hansen@linux.intel.com,
        colin.i.king@gmail.com, jim.cromie@gmail.com,
        catalin.marinas@arm.com, jbaron@akamai.com,
        rick.p.edgecombe@intel.com, yujie.liu@intel.com, david@redhat.com,
        tglx@linutronix.de, hch@lst.de, patches@lists.linux.dev,
        linux-modules@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, pmladek@suse.com, prarit@redhat.com,
        lennart@poettering.net
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On Mon, May 29, 2023 at 4:58=E2=80=AFAM Johan Hovold <johan@kernel.org> wro=
te:
>
> I have not tried to figure out exactly why things break, but it does
> seem like this one should be reverted.

Yes, I have done so.

However, can I ask you to just verify that it was purely the exclusive
open part, and it wasn't that I messed up something else. IOW, can you
replace the

        return exclusive_deny_write_access(file);

in prepare_file_for_module_load() with just a "return 0", and remove the

                allow_write_access(f.file);

line in finit_module()?

That's obviously _instead_ of the revert that I already pushed out,
just to verify that "yup, it's that part, not something silly
elsewhere"

I do wonder what it is that is different in your setup, and maybe you
could also enable the

        pr_debug("finit_module: fd=3D%d, uargs=3D%p, flags=3D%i\n", fd, uar=
gs, flags);

in finit_module() while you are at it? Since you'd be editing that
file anyway for the test, just change the pr_debug() to a printk() and
then do

    dmesg | grep finit_module

to see what it all results in (on a working kernel, of course).

                    Linus