Re: [PATCH v2] Fix regression due to "fs: move binfmt_misc sysctl to its own file"

[Tong Zhang <ztong0001@xxxxxxxxx>]

On Feb 13, 2022, at 7:34 AM, Ido Schimmel <idosch@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxx/

Thanks,

- Tong