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

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Message-ID: <984e6c0f-ec87-a2e0-8463-28fb9130b4b6@kernel.org>
Date:   Thu, 8 Sep 2022 18:54:44 +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 2022/8/31 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
> 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.

Nice catch!

Could you please check:

f2fs: fix to detect obsolete inner inode during fill_super()

Thanks,

> 
>>
>>>
>>> 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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