linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix deadlock between quota writes and checkpoint

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Message-ID: <9a35fddd-2b67-c91e-2b1a-c63a285cd4ab@huawei.com>
Date:   Tue, 4 Aug 2020 15:57:13 +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>, Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix deadlock between quota writes and
 checkpoint

On 2020/8/4 11:54, Jaegeuk Kim wrote:
> On 08/04, Chao Yu wrote:
>> On 2020/7/29 15:02, Jaegeuk Kim wrote:
>>> f2fs_write_data_pages(quota_mapping)
>>>    __f2fs_write_data_pages             f2fs_write_checkpoint
>>>     * blk_start_plug(&plug);
>>>     * add bio in write_io[DATA]
>>>                                         - block_operations
>>>                                         - skip syncing quota by
>>>                                                   >DEFAULT_RETRY_QUOTA_FLUSH_COUNT
>>>                                         - down_write(&sbi->node_write);
>>
>> f2fs_flush_merged_writes() will be called after block_operations(), why this doesn't
>> help?
> 
> Well, I think bio can be added after f2fs_flush_merged_writes() as well.

- down_read(node_write)
- f2fs_do_write_data_page
  - f2fs_trylock_op
   - f2fs_outplace_write_data
      - f2fs_submit_page_write

bio only be added under node_write lock? during f2fs_flush_merged_writes(), node_write
should have been held by checkpoint() avoiding quota data writeback & bio submission.

> 
>>
>>>     - f2fs_write_single_data_page
>>>       - f2fs_do_write_data_page
>>>         - f2fs_outplace_write_data
>>>           - do_write_page
>>>              - f2fs_allocate_data_block
>>>               - down_write(node_write)
>>>                                         - f2fs_wait_on_all_pages(F2FS_WB_CP_DATA);
>>>
>>> Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>>    fs/f2fs/checkpoint.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>> index 8c782d3f324f0..99c8061da55b9 100644
>>> --- a/fs/f2fs/checkpoint.c
>>> +++ b/fs/f2fs/checkpoint.c
>>> @@ -1269,6 +1269,8 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>>>    		if (type == F2FS_DIRTY_META)
>>>    			f2fs_sync_meta_pages(sbi, META, LONG_MAX,
>>>    							FS_CP_META_IO);
>>> +		else if (type == F2FS_WB_CP_DATA)
>>> +			f2fs_submit_merged_write(sbi, DATA);
>>>    		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
>>>    	}
>>>    	finish_wait(&sbi->cp_wait, &wait);
>>>
> .
>