linux-kernel - Re: [PATCH] Fix regression due to "fs: move binfmt

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Message-ID: <YgKmaggsipzzCGCg@bombadil.infradead.org>
Date:   Tue, 8 Feb 2022 09:20:42 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Tong Zhang <ztong0001@...il.com>
Cc:     Domenico Andreoli <domenico.andreoli@...ux.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Airlie <airlied@...ux.ie>,
        Andrew Morton <akpm@...ux-foundation.org>, amir73il@...il.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, bcrl@...ck.org,
        benh@...nel.crashing.org, clemens@...isch.de, crope@....fi,
        dgilbert@...erlog.com, Greg KH <gregkh@...uxfoundation.org>,
        jack@...e.cz, jani.nikula@...el.com, jani.nikula@...ux.intel.com,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>, jlbec@...lplan.org,
        john.ogness@...utronix.de, joonas.lahtinen@...ux.intel.com,
        Joseph Qi <joseph.qi@...ux.alibaba.com>, julia.lawall@...ia.fr,
        Kees Cook <keescook@...omium.org>, kernel@...force.de,
        Linux Memory Management List <linux-mm@...ck.org>,
        mark@...heh.com, "Martin K. Petersen" <martin.petersen@...cle.com>,
        mm-commits@...r.kernel.org, nixiaoming@...wei.com,
        penguin-kernel@...ove.sakura.ne.jp, peterz@...radead.org,
        phil@...lpotter.co.uk, pjt@...gle.com, pmladek@...e.com,
        rafael@...nel.org, rodrigo.vivi@...el.com, rostedt@...dmis.org,
        senozhatsky@...omium.org, sre@...nel.org, steve@....org,
        surenb@...gle.com, torvalds@...ux-foundation.org, tytso@....edu,
        Al Viro <viro@...iv.linux.org.uk>, wangqing@...o.com,
        Iurii Zaikin <yzaikin@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix regression due to "fs: move binfmt_misc sysctl to
 its own file"

On Mon, Feb 07, 2022 at 02:53:21PM -0800, Tong Zhang wrote:
> On Mon, Feb 7, 2022 at 1:46 PM Luis Chamberlain <mcgrof@...nel.org> wrote:
> >
> > OK I think the issue here should have been that declaring this on
> > fs/binfmt_misc.c creates the chicken and the egg issue, and so we
> > need to do this on built-in code. Instead of your patch can you try
> > this instead, it just always creates the sysctl mount always now
> > so long as proc sysctl is enabled. It does not do the unregistration
> > as we always want the path present as it used to be before as well.
> >
> > diff --git a/fs/file_table.c b/fs/file_table.c
> > index 57edef16dce4..4f4739c9405c 100644
> > --- a/fs/file_table.c
> > +++ b/fs/file_table.c
> > @@ -119,6 +119,7 @@ static struct ctl_table fs_stat_sysctls[] = {
> >  static int __init init_fs_stat_sysctls(void)
> >  {
> >         register_sysctl_init("fs", fs_stat_sysctls);
> > +       register_sysctl_mount_point("fs/binfmt_misc");
> >         return 0;
> >  }
> >  fs_initcall(init_fs_stat_sysctls);
> 
> I'm looking at the original code, and it seems that if we don't select
> CONFIG_BINFMT_MISC at all,
> this file won't be created. This would suggest an IF MACRO around
> > +       register_sysctl_mount_point("fs/binfmt_misc");
> and it should looks like
> +#if IS_ENABLED(CONFIG_BINFMT_MISC)
> +       register_sysctl_mount_point("fs/binfmt_misc");
> +#endif
> or if you prefer original style:
> #if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)

Or better yet using IS_ENABLED() to avoid the ifdef cruft:

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index c07f35719ee3..4b8f1b11a7c8 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -817,20 +817,16 @@ static struct file_system_type bm_fs_type = {
 };
 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;
 }
 
 static void __exit exit_misc_binfmt(void)
 {
-	unregister_sysctl_table(binfmt_misc_header);
 	unregister_binfmt(&misc_format);
 	unregister_filesystem(&bm_fs_type);
 }
diff --git a/fs/file_table.c b/fs/file_table.c
index 57edef16dce4..4969021fa676 100644
--- 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");
 	return 0;
 }
 fs_initcall(init_fs_stat_sysctls);