Fix regression due to "fs: move binfmt_misc sysctl to its own file"

Commit 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file") did
not go unnoticed, binfmt-support stopped to work on my Debian system
since v5.17-rc2 (did not check with -rc1).

The existance of the /proc/sys/fs/binfmt_misc is a precondition for
attempting to mount the binfmt_misc fs, which in turn triggers the
autoload of the binfmt_misc module.  Without it, no module is loaded and
no binfmt is available at boot.

Building as built-in or manually loading the module and mounting the fs
works fine, it's therefore only a matter of interaction with user-space.
I could try to improve the Debian systemd configuration but I can't say
anything about the other distributions.

This patch restores a working system right after boot.

Fixes: 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file")
Signed-off-by: Domenico Andreoli <domenico.andreoli@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Tong Zhang <ztong0001@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

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);