linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: don't skip writeback of quota data

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Message-ID: <d8645371-f1d6-f5a2-01a9-19708fe3861b@huawei.com>
Date:   Tue, 14 Jul 2020 20:14:46 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>, <kernel-team@...roid.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: don't skip writeback of quota data

On 2020/7/14 1:59, Jaegeuk Kim wrote:
> On 07/10, Chao Yu wrote:
>> On 2020/7/10 11:50, Jaegeuk Kim wrote:
>>> On 07/10, Chao Yu wrote:
>>>> On 2020/7/10 11:26, Jaegeuk Kim wrote:
>>>>> On 07/10, Chao Yu wrote:
>>>>>> On 2020/7/10 3:05, Jaegeuk Kim wrote:
>>>>>>> On 07/09, Chao Yu wrote:
>>>>>>>> On 2020/7/9 13:30, Jaegeuk Kim wrote:
>>>>>>>>> It doesn't need to bypass flushing quota data in background.
>>>>>>>>
>>>>>>>> The condition is used to flush quota data in batch to avoid random
>>>>>>>> small-sized udpate, did you hit any problem here?
>>>>>>>
>>>>>>> I suspect this causes fault injection test being stuck by waiting for inode
>>>>>>> writeback completion. With this patch, it has been running w/o any issue so far.
>>>>>>> I keep an eye on this.
>>>>>>
>>>>>> Hmmm.. so that this patch may not fix the root cause, and it may hiding the
>>>>>> issue deeper.
>>>>>>
>>>>>> How about just keeping this patch in our private branch to let fault injection
>>>>>> test not be stuck? until we find the root cause in upstream codes.
>>>>>
>>>>> Well, I don't think this hides something. When the issue happens, I saw inodes
>>>>> being stuck due to writeback while only quota has some dirty data. At that time,
>>>>> there was no dirty data page from other inodes.
>>>>
>>>> Okay,
>>>>
>>>>>
>>>>> More specifically, I suspect __writeback_inodes_sb_nr() gives WB_SYNC_NONE and
>>>>> waits for wb_wait_for_completion().
>>>>
>>>> Did you record any callstack after the issue happened?
>>>
>>> I found this.
>>>
>>> [213389.297642]  __schedule+0x2dd/0x780^M
>>> [213389.299224]  schedule+0x55/0xc0^M
>>> [213389.300745]  wb_wait_for_completion+0x56/0x90^M
>>> [213389.302469]  ? wait_woken+0x80/0x80^M
>>> [213389.303997]  __writeback_inodes_sb_nr+0xa8/0xd0^M
>>> [213389.305760]  writeback_inodes_sb+0x4b/0x60^M
>>> [213389.307439]  sync_filesystem+0x2e/0xa0^M
>>> [213389.308999]  generic_shutdown_super+0x27/0x110^M
>>> [213389.310738]  kill_block_super+0x27/0x50^M
>>> [213389.312327]  kill_f2fs_super+0x76/0xe0 [f2fs]^M
>>> [213389.314014]  deactivate_locked_super+0x3b/0x80^M
>>> [213389.315692]  deactivate_super+0x3e/0x50^M
>>> [213389.317226]  cleanup_mnt+0x109/0x160^M
>>> [213389.318718]  __cleanup_mnt+0x12/0x20^M
>>> [213389.320177]  task_work_run+0x70/0xb0^M
>>> [213389.321609]  exit_to_usermode_loop+0x131/0x160^M
>>> [213389.323306]  do_syscall_64+0x170/0x1b0^M
>>> [213389.324762]  entry_SYSCALL_64_after_hwframe+0x44/0xa9^M
>>> [213389.326477] RIP: 0033:0x7fc4b5e6a35b^M
>>
>> Does this only happen during umount? If so, will below change help?
>>
>> 	if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
>> +			!is_sbi_flag_set(sbi, SBI_IS_CLOSE) &&
>> 			wbc->sync_mode == WB_SYNC_NONE &&
>> 			get_dirty_pages(inode) < nr_pages_to_skip(sbi, DATA) &&
>> 			f2fs_available_free_memory(sbi, DIRTY_DENTS))
>> 		goto skip_write;
> 
> Hmm, this doesn't work. The writeback was called before put_super?

Oops, still be confused about this issue. :(

Thanks,

> I'll try the original patch one more time.
> 
>>
>>>
>>>>
>>>> Still I'm confused that why directory's data written could be skipped, but
>>>> quota's data couldn't, what's the difference?
>>>
>>> I suspect different blocking timing from cp_error between quota and dentry.
>>> e.g., we block dir operations right after cp_error, while quota can make
>>
>> No guarantee that there is no dirty dentry being created after
>> cp_error, right?
>>
>> e.g.
>>
>> Thread A				Thread B
>> - f2fs_create
>> - bypass f2fs_cp_error
>> 					- set cp_error
>> - create dirty dentry
>>
>> BTW, do you know what __writeback_inodes_sb_nr is waiting for?
>>
>>> dirty pages in more fine granularity.
>>>
>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>>>>>>>> ---
>>>>>>>>>  fs/f2fs/data.c | 2 +-
>>>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>>>>>> index 44645f4f914b6..72e8b50e588c1 100644
>>>>>>>>> --- a/fs/f2fs/data.c
>>>>>>>>> +++ b/fs/f2fs/data.c
>>>>>>>>> @@ -3148,7 +3148,7 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
>>>>>>>>>  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
>>>>>>>>>  		goto skip_write;
>>>>>>>>>  
>>>>>>>>> -	if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
>>>>>>>>> +	if (S_ISDIR(inode->i_mode) &&
>>>>>>>>>  			wbc->sync_mode == WB_SYNC_NONE &&
>>>>>>>>>  			get_dirty_pages(inode) < nr_pages_to_skip(sbi, DATA) &&
>>>>>>>>>  			f2fs_available_free_memory(sbi, DIRTY_DENTS))
>>>>>>>>>
>>>>>>> .
>>>>>>>
>>>>> .
>>>>>
>>> .
>>>
> .
>