linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix missing mapping caused by the mount/umount race

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Date:   Wed, 14 Sep 2022 23:28:31 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     syzbot+775a3440817f74fddb8c@...kaller.appspotmail.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix missing mapping caused by the
 mount/umount race

On 2022/9/14 23:15, Jaegeuk Kim wrote:
> On 09/14, Chao Yu wrote:
>> On 2022/8/31 11:05, Jaegeuk Kim wrote:
>>> On 08/30, Jaegeuk Kim wrote:
>>>> On 08/30, Chao Yu wrote:
>>>>> On 2022/8/30 5:52, Jaegeuk Kim wrote:
>>>>>> Sometimes we can get a cached meta_inode which has no aops yet. Let's set it
>>>>>> all the time to fix the below panic.
>>>>>>
>>>>>> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
>>>>>> Mem abort info:
>>>>>>      ESR = 0x0000000086000004
>>>>>>      EC = 0x21: IABT (current EL), IL = 32 bits
>>>>>>      SET = 0, FnV = 0
>>>>>>      EA = 0, S1PTW = 0
>>>>>>      FSC = 0x04: level 0 translation fault
>>>>>> user pgtable: 4k pages, 48-bit VAs, pgdp=0000000109ee4000
>>>>>> [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
>>>>>> Internal error: Oops: 86000004 [#1] PREEMPT SMP
>>>>>> Modules linked in:
>>>>>> CPU: 1 PID: 3045 Comm: syz-executor330 Not tainted 6.0.0-rc2-syzkaller-16455-ga41a877bc12d #0
>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
>>>>>> pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>>>>>> pc : 0x0
>>>>>> lr : folio_mark_dirty+0xbc/0x208 mm/page-writeback.c:2748
>>>>>> sp : ffff800012783970
>>>>>> x29: ffff800012783970 x28: 0000000000000000 x27: ffff800012783b08
>>>>>> x26: 0000000000000001 x25: 0000000000000400 x24: 0000000000000001
>>>>>> x23: ffff0000c736e000 x22: 0000000000000045 x21: 05ffc00000000015
>>>>>> x20: ffff0000ca7403b8 x19: fffffc00032ec600 x18: 0000000000000181
>>>>>> x17: ffff80000c04d6bc x16: ffff80000dbb8658 x15: 0000000000000000
>>>>>> x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
>>>>>> x11: ff808000083e9814 x10: 0000000000000000 x9 : ffff8000083e9814
>>>>>> x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
>>>>>> x5 : ffff0000cbb19000 x4 : ffff0000cb3d2000 x3 : ffff0000cbb18f80
>>>>>> x2 : fffffffffffffff0 x1 : fffffc00032ec600 x0 : ffff0000ca7403b8
>>>>>> Call trace:
>>>>>>     0x0
>>>>>>     set_page_dirty+0x38/0xbc mm/folio-compat.c:62
>>>>>>     f2fs_update_meta_page+0x80/0xa8 fs/f2fs/segment.c:2369
>>>>>>     do_checkpoint+0x794/0xea8 fs/f2fs/checkpoint.c:1522
>>>>>>     f2fs_write_checkpoint+0x3b8/0x568 fs/f2fs/checkpoint.c:1679
>>>>>>
>>>>>> Cc: stable@...r.kernel.org
>>>>>> Reported-by: syzbot+775a3440817f74fddb8c@...kaller.appspotmail.com
>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>>>>> ---
>>>>>>     fs/f2fs/inode.c | 13 ++++++++-----
>>>>>>     1 file changed, 8 insertions(+), 5 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>>>>> index 6d11c365d7b4..1feb0a8a699e 100644
>>>>>> --- a/fs/f2fs/inode.c
>>>>>> +++ b/fs/f2fs/inode.c
>>>>>> @@ -490,10 +490,7 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
>>>>>>     	if (!inode)
>>>>>>     		return ERR_PTR(-ENOMEM);
>>>>>> -	if (!(inode->i_state & I_NEW)) {
>>>>>> -		trace_f2fs_iget(inode);
>>>>>> -		return inode;
>>>>>> -	}
>>>>>> +	/* We can see an old cached inode. Let's set the aops all the time. */
>>>>>
>>>>> Why an old cached inode (has no I_NEW flag) has NULL a_ops pointer? If it is a bad
>>>>> inode, it should be unhashed before unlock_new_inode().
>>>>
>>>> I'm trying to dig further tho, it's not a bad inode, nor I_FREEING | I_CLEAR.
>>>> It's very werid that thie meta inode is found in newly created superblock by
>>>> the global hash table. I've checked that the same superblock pointer was used
>>>> in the previous tests, but inode was evictied all the time.
>>>
>>> I'll drop this patch, since it turned out there is a bug in reiserfs which
>>> doesn't free the root inode (ino=2). That leads f2fs to find an ino=2 with
>>> the previous superblock point used by reiserfs. That stale inode has no valid
>>
>> One more question, why stale inode could be remained in inode hash table,
>> shouldn't the stale inode be evicted/unhashed in below path during reiserfs
>> umount:
>>
>> - reiserfs_kill_sb
>>   - kill_block_super
>>    - generic_shutdown_super
>>     - evict_inodes
>>      - dispose_list
>>       - evict
>>        - remove_inode_hash
> 
> Yes, that's why I didn't dive into further, as it's odd.

Alright, this bug was reproducable w/ below testcase, right? :)

C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=167b5e33080000

Thanks,

> 
>>
>> Thanks,
>>
>>> inode that f2fs can use. I tried to find where the root cause is in reiserfs,
>>> but it seems quite hard to catch one.
>>>
>>> - reiserfs_fill_super
>>>    - reiserfs_xattr_init
>>>     - create_privroot
>>>      - xattr_mkdir
>>>       - reiserfs_new_inode
>>>        - reiserfs_get_unused_objectid returned 0 due to map crash
>>>
>>> It seems the error path doesn't handle the root inode properly.
>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>>>     	if (ino == F2FS_NODE_INO(sbi) || ino == F2FS_META_INO(sbi))
>>>>>>     		goto make_now;
>>>>>> @@ -502,6 +499,11 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
>>>>>>     		goto make_now;
>>>>>>     #endif
>>>>>> +	if (!(inode->i_state & I_NEW)) {
>>>>>> +		trace_f2fs_iget(inode);
>>>>>> +		return inode;
>>>>>> +	}
>>>>>> +
>>>>>>     	ret = do_read_inode(inode);
>>>>>>     	if (ret)
>>>>>>     		goto bad_inode;
>>>>>> @@ -557,7 +559,8 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
>>>>>>     		file_dont_truncate(inode);
>>>>>>     	}
>>>>>> -	unlock_new_inode(inode);
>>>>>> +	if (inode->i_state & I_NEW)
>>>>>> +		unlock_new_inode(inode);
>>>>>>     	trace_f2fs_iget(inode);
>>>>>>     	return inode;
>>>>
>>>>
>>>> _______________________________________________
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>>>> Linux-f2fs-devel@...ts.sourceforge.net
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