linux-kernel - Re: [PATCH 2/2] module: add support to avoid duplicates early on load

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Message-ID: <CAHk-=wh6sXSO63kka+EWEqq0tGwtOnXYFWMXPQ6T_wZa+Np3MQ@mail.gmail.com>
Date:   Mon, 29 May 2023 07:00:05 -0400
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Petr Pavlu <petr.pavlu@...e.com>, gregkh@...uxfoundation.org,
        rafael@...nel.org, song@...nel.org, lucas.de.marchi@...il.com,
        christophe.leroy@...roup.eu, peterz@...radead.org, rppt@...nel.org,
        dave@...olabs.net, willy@...radead.org, vbabka@...e.cz,
        mhocko@...e.com, dave.hansen@...ux.intel.com,
        colin.i.king@...il.com, jim.cromie@...il.com,
        catalin.marinas@....com, jbaron@...mai.com,
        rick.p.edgecombe@...el.com, yujie.liu@...el.com, david@...hat.com,
        tglx@...utronix.de, hch@....de, patches@...ts.linux.dev,
        linux-modules@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, pmladek@...e.com, prarit@...hat.com,
        lennart@...ttering.net
Subject: Re: [PATCH 2/2] module: add support to avoid duplicates early on load

On Mon, May 29, 2023 at 4:58 AM Johan Hovold <johan@...nel.org> wrote:
>
> 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=%d, uargs=%p, flags=%i\n", fd, uargs, 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