Re: [PATCH 1/2] ext4: alloc test super block from sget

[Christian Brauner]

On Fri, Mar 01, 2024 at 08:08:15PM +0800, Kemeng Shi wrote:
> This fix the oops in ext4 unit test which is cuased by NULL sb.s_user_ns
> as following:
> <4>[ 14.344565] map_id_range_down (kernel/user_namespace.c:318)
> <4>[ 14.345378] make_kuid (kernel/user_namespace.c:415)
> <4>[ 14.345998] inode_init_always (include/linux/fs.h:1375 fs/inode.c:174)
> <4>[ 14.346696] alloc_inode (fs/inode.c:268)
> <4>[ 14.347353] new_inode_pseudo (fs/inode.c:1007)
> <4>[ 14.348016] new_inode (fs/inode.c:1033)
> <4>[ 14.348644] ext4_mb_init (fs/ext4/mballoc.c:3404 fs/ext4/mballoc.c:3719)
> <4>[ 14.349312] mbt_kunit_init (fs/ext4/mballoc-test.c:57
> fs/ext4/mballoc-test.c:314)
> <4>[ 14.349983] kunit_try_run_case (lib/kunit/test.c:388 lib/kunit/test.c:443)
> <4>[ 14.350696] kunit_generic_run_threadfn_adapter (lib/kunit/try-catch.c:30)
> <4>[ 14.351530] kthread (kernel/kthread.c:388)
> <4>[ 14.352168] ret_from_fork (arch/arm64/kernel/entry.S:861)
> <0>[ 14.353385] Code: 52808004 b8236ae7 72be5e44 b90004c4 (38e368a1)
> 
> Alloc test super block from sget to properly initialize test super block
> to fix the issue.
> 
> Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
> Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
>  fs/ext4/mballoc-test.c | 46 ++++++++++++++++++++++++++++--------------
>  1 file changed, 31 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/ext4/mballoc-test.c b/fs/ext4/mballoc-test.c
> index 12d0b22cabe1..1da52bbf4599 100644
> --- a/fs/ext4/mballoc-test.c
> +++ b/fs/ext4/mballoc-test.c
> @@ -21,16 +21,27 @@ struct mbt_ctx {
>  };
>  
>  struct mbt_ext4_super_block {
> -	struct super_block sb;
> +	struct ext4_super_block es;
> +	struct ext4_sb_info sbi;
>  	struct mbt_ctx mbt_ctx;
>  };
>  
> -#define MBT_CTX(_sb) (&(container_of((_sb), struct mbt_ext4_super_block, sb)->mbt_ctx))
> +#define MBT_SB(_sb) (container_of((_sb)->s_fs_info, struct mbt_ext4_super_block, sbi))
> +#define MBT_CTX(_sb) (&MBT_SB(_sb)->mbt_ctx)
>  #define MBT_GRP_CTX(_sb, _group) (&MBT_CTX(_sb)->grp_ctx[_group])
>  
>  static const struct super_operations mbt_sops = {
>  };
>  
> +static void mbt_kill_sb(struct super_block *sb)
> +{
> +}
> +
> +static struct file_system_type mbt_fs_type = {
> +	.name			= "mballoc test",
> +	.kill_sb		= mbt_kill_sb,
> +};
> +
>  static int mbt_mb_init(struct super_block *sb)
>  {
>  	int ret;
> @@ -72,43 +83,48 @@ static void mbt_mb_release(struct super_block *sb)
>  	kfree(sb->s_bdev);
>  }
>  
> +static int mbt_set(struct super_block *sb, void *data)
> +{
> +	return 0;
> +}
> +
>  static struct super_block *mbt_ext4_alloc_super_block(void)
>  {
> -	struct ext4_super_block *es = kzalloc(sizeof(*es), GFP_KERNEL);
> -	struct ext4_sb_info *sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>  	struct mbt_ext4_super_block *fsb = kzalloc(sizeof(*fsb), GFP_KERNEL);
> +	struct super_block *sb = sget(&mbt_fs_type, NULL, mbt_set, 0, NULL);
> +	struct ext4_sb_info *sbi;
>  
> -	if (fsb == NULL || sbi == NULL || es == NULL)
> +	if (fsb == NULL || sb == NULL)

sget() returns error pointer on failure. So you should check for IS_ERR(sb).