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Message-ID: <27143c70-906e-a575-ef58-ac9f3c5ab080@bytedance.com>
Date:   Tue, 13 Sep 2022 12:52:41 +0800
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Subject: Re: [External] Re: [PATCH V2 4/5] erofs: remove duplicated
 unregister_cookie
To:     JeffleXu <jefflexu@linux.alibaba.com>,
        linux-erofs@lists.ozlabs.org, xiang@kernel.org, chao@kernel.org
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        yinxin.x@bytedance.com, huyue2@coolpad.com
References: <20220902105305.79687-1-zhujia.zj@bytedance.com>
 <20220902105305.79687-5-zhujia.zj@bytedance.com>
 <3f75d266-7ccd-be6d-657c-fe0633b25687@linux.alibaba.com>
 <8a239157-de28-44ae-edef-336092c34a15@linux.alibaba.com>
From:   Jia Zhu <zhujia.zj@bytedance.com>
In-Reply-To: <8a239157-de28-44ae-edef-336092c34a15@linux.alibaba.com>
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在 2022/9/9 18:28, JeffleXu 写道:
> 
> 
> On 9/9/22 5:55 PM, JeffleXu wrote:
>>
>>
>> On 9/2/22 6:53 PM, Jia Zhu wrote:
>>> In erofs umount scenario, erofs_fscache_unregister_cookie() is called
>>> twice in kill_sb() and put_super().
>>>
>>> It works for original semantics, cause 'ctx' will be set to NULL in
>>> put_super() and will not be unregister again in kill_sb().
>>> However, in shared domain scenario, we use refcount to maintain the
>>> lifecycle of cookie. Unregister the cookie twice will cause it to be
>>> released early.
> 
> Sorry, why can't we also set sbi->s_fscache to NULL after decrementing
> the refcount in shared domain mode, to avoid the refcount being
> decremented twice?
> 
In below case:
1. mount -t erofs none -o fsid=bootstrap.img -o device=blob.img -o 
domain_id=1 mnt
2. mount -t erofs none -o fsid=bootstrap.img -o device=blob.img -o 
domain_id=1 mnt2
3. Procedure 2 will fail since we can't mount erofs with the same sysfs
entry.
4. Mount()'s error handling path will step into put_super().
5. Domain's refcnt will be decremented even if it has not yet
been incremented.
>>>
>>> For the above reasons, this patch removes duplicate unregister_cookie
>>> and move fscache_unregister_* before shotdown_super() to prevent busy
>>> inode(ctx->inode) when umount.
>>>
>>> Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
>>> ---
>>>   fs/erofs/super.c | 16 ++++++++--------
>>>   1 file changed, 8 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>>> index 69de1731f454..667a78f0ee70 100644
>>> --- a/fs/erofs/super.c
>>> +++ b/fs/erofs/super.c
>>> @@ -919,19 +919,20 @@ static void erofs_kill_sb(struct super_block *sb)
>>>   		kill_litter_super(sb);
>>>   		return;
>>>   	}
>>> -	if (erofs_is_fscache_mode(sb))
>>> -		generic_shutdown_super(sb);
>>> -	else
>>> -		kill_block_super(sb);
>>> -
>>>   	sbi = EROFS_SB(sb);
>>>   	if (!sbi)
>>>   		return;
>>>   
>>> +	if (erofs_is_fscache_mode(sb)) {
>>> +		erofs_fscache_unregister_cookie(&sbi->s_fscache);
>>> +		erofs_fscache_unregister_fs(sb);
>>> +		generic_shutdown_super(sb);
>>
>> Generally we can't do clean ups before generic_shutdown_super(), since
>> generic_shutdown_super() may trigger IO, e.g. in sync_filesystem(),
>> though it's not the case for erofs (read-only).
>>
>> How about embedding erofs_fscache_unregister_cookie() into
>> erofs_fscache_unregister_fs(), and thus we can check domain_id in
>> erofs_fscache_unregister_fs()?
>>
>>> +	} else {
>>> +		kill_block_super(sb);
>>> +	}
>>> +
>>>   	erofs_free_dev_context(sbi->devs);
>>>   	fs_put_dax(sbi->dax_dev, NULL);
>>> -	erofs_fscache_unregister_cookie(&sbi->s_fscache);
>>> -	erofs_fscache_unregister_fs(sb);
>>>   	kfree(sbi->opt.fsid);
>>>   	kfree(sbi->opt.domain_id);
>>>   	kfree(sbi);
>>> @@ -951,7 +952,6 @@ static void erofs_put_super(struct super_block *sb)
>>>   	iput(sbi->managed_cache);
>>>   	sbi->managed_cache = NULL;
>>>   #endif
>>> -	erofs_fscache_unregister_cookie(&sbi->s_fscache);
>>>   }
>>>   
>>>   struct file_system_type erofs_fs_type = {
>>
>