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From:   Tong Zhang <ztong0001@gmail.com>
Date:   Sun, 13 Feb 2022 13:10:42 -0800
Message-ID: <CAA5qM4AP=pOi1dFFgELJ97nSwTBqrruseGmTF-qab=xj2==_Xg@mail.gmail.com>
Subject: Re: [PATCH v2] Fix regression due to "fs: move binfmt_misc sysctl to
 its own file"
To:     Ido Schimmel <idosch@idosch.org>
Cc:     Domenico Andreoli <domenico.andreoli@linux.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        David Airlie <airlied@linux.ie>,
        Andrew Morton <akpm@linux-foundation.org>, amir73il@gmail.com,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>, bcrl@kvack.org,
        benh@kernel.crashing.org, clemens@ladisch.de, crope@iki.fi,
        dgilbert@interlog.com, Greg KH <gregkh@linuxfoundation.org>,
        jack@suse.cz, jani.nikula@intel.com,
        Jani Nikula <jani.nikula@linux.intel.com>,
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        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Joseph Qi <joseph.qi@linux.alibaba.com>, julia.lawall@inria.fr,
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On Sun, Feb 13, 2022 at 7:34 AM Ido Schimmel <idosch@idosch.org> wrote:
>
> On Wed, Feb 09, 2022 at 08:49:20AM +0100, Domenico Andreoli wrote:
> >  fs/binfmt_misc.c |    6 +-----
> >  fs/file_table.c  |    2 ++
> >  2 files changed, 3 insertions(+), 5 deletions(-)
> >
> > Index: b/fs/binfmt_misc.c
> > ===================================================================
> > --- a/fs/binfmt_misc.c
> > +++ b/fs/binfmt_misc.c
> > @@ -817,20 +817,16 @@ static struct file_system_type bm_fs_typ
> >  };
> >  MODULE_ALIAS_FS("binfmt_misc");
> >
> > -static struct ctl_table_header *binfmt_misc_header;
> > -
> >  static int __init init_misc_binfmt(void)
> >  {
> >       int err = register_filesystem(&bm_fs_type);
> >       if (!err)
> >               insert_binfmt(&misc_format);
> > -     binfmt_misc_header = register_sysctl_mount_point("fs/binfmt_misc");
> > -     return 0;
> > +     return err;
> >  }
> >
> >  static void __exit exit_misc_binfmt(void)
> >  {
> > -     unregister_sysctl_table(binfmt_misc_header);
> >       unregister_binfmt(&misc_format);
> >       unregister_filesystem(&bm_fs_type);
> >  }
> > Index: b/fs/file_table.c
> > ===================================================================
> > --- a/fs/file_table.c
> > +++ b/fs/file_table.c
> > @@ -119,6 +119,8 @@ static struct ctl_table fs_stat_sysctls[
> >  static int __init init_fs_stat_sysctls(void)
> >  {
> >       register_sysctl_init("fs", fs_stat_sysctls);
> > +     if (IS_ENABLED(CONFIG_BINFMT_MISC))
> > +             register_sysctl_mount_point("fs/binfmt_misc");
>
> Hi,
>
> kmemleak complains about this:
>
> # cat /sys/kernel/debug/kmemleak
> unreferenced object 0xffff8881045fea88 (size 96):
>   comm "swapper/0", pid 1, jiffies 4294669355 (age 167.804s)
>   hex dump (first 32 bytes):
>     e0 c8 07 88 ff ff ff ff 00 00 00 00 01 00 00 00  ................
>     01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<ffffffff81d11637>] __register_sysctl_table+0x117/0x1150
>     [<ffffffff86c3600f>] init_fs_stat_sysctls+0x30/0x33
>     [<ffffffff81002558>] do_one_initcall+0x108/0x690
>     [<ffffffff86bca8bd>] kernel_init_freeable+0x45a/0x4de
>     [<ffffffff83e0757f>] kernel_init+0x1f/0x220
>     [<ffffffff810048cf>] ret_from_fork+0x1f/0x30
>
> >       return 0;
> >  }
> >  fs_initcall(init_fs_stat_sysctls);
> >

Hi Ido,
Thanks for the report. This is a known issue. The fix is proposed here.
https://lore.kernel.org/all/YgRbEG21AUrLSFKX@bombadil.infradead.org/

Thanks,
- Tong