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

[Kemeng Shi]

on 3/1/2024 4:25 PM, Christian Brauner wrote:
> 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).
> 
Thanks a lot for review. I will fix it in next version.