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Subject: Re: [PATCH] Revert "f2fs: fix quota_sync failure due to f2fs_lock_op"
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
References: <20200529092947.7890-1-yuchao0@huawei.com>
 <20200529223426.GA249109@google.com>
 <96ba756e-a354-1ee8-689e-211f63c294e6@huawei.com>
 <20200530014926.GA39950@google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <dcd3564c-16c3-4e4c-a21f-7fec46cec181@huawei.com>
Date:   Sat, 30 May 2020 10:02:57 +0800
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On 2020/5/30 9:49, Jaegeuk Kim wrote:
> On 05/30, Chao Yu wrote:
>> On 2020/5/30 6:34, Jaegeuk Kim wrote:
>>> On 05/29, Chao Yu wrote:
>>>> Under heavy fsstress, we may triggle panic while issuing discard,
>>>> because __check_sit_bitmap() detects that discard command may earse
>>>> valid data blocks, the root cause is as below race stack described,
>>>> since we removed lock when flushing quota data, quota data writeback
>>>> may race with write_checkpoint(), so that it causes inconsistency in
>>>> between cached discard entry and segment bitmap.
>>>>
>>>> - f2fs_write_checkpoint
>>>>  - block_operations
>>>>   - set_sbi_flag(sbi, SBI_QUOTA_SKIP_FLUSH)
>>>>  - f2fs_flush_sit_entries
>>>>   - add_discard_addrs
>>>>    - __set_bit_le(i, (void *)de->discard_map);
>>>> 						- f2fs_write_data_pages
>>>> 						 - f2fs_write_single_data_page
>>>> 						   : inode is quota one, cp_rwsem won't be locked
>>>> 						  - f2fs_do_write_data_page
>>>> 						   - f2fs_allocate_data_block
>>>> 						    - f2fs_wait_discard_bio
>>>> 						      : discard entry has not been added yet.
>>>> 						    - update_sit_entry
>>>>  - f2fs_clear_prefree_segments
>>>>   - f2fs_issue_discard
>>>>   : add discard entry
>>>>
>>>> This patch fixes this issue by reverting 435cbab95e39 ("f2fs: fix quota_sync
>>>> failure due to f2fs_lock_op").
>>>>
>>>> Fixes: 435cbab95e39 ("f2fs: fix quota_sync failure due to f2fs_lock_op")
>>>
>>> The previous patch fixes quota_sync gets EAGAIN all the time.
>>> How about this? It seems this works for fsstress test.
>>>
> 
> Then this?
> 
> ---
>  fs/f2fs/segment.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index ebbadde6cbced..ed11dcf2d69ed 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -3107,6 +3107,14 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
>  		type = CURSEG_COLD_DATA;
>  	}
>  
> +	/*
> +	 * We need to wait for node_write to avoid block allocation during
> +	 * checkpoint. This can only happen to quota writes which can cause
> +	 * the below discard race condition.
> +	 */
> +	if (IS_DATASEG(type))
> +		down_write(&sbi->node_write);
> +
>  	down_read(&SM_I(sbi)->curseg_lock);
>  
>  	mutex_lock(&curseg->curseg_mutex);
> @@ -3174,6 +3182,9 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,

Minor thing: unlock order.

if (IS_DATASEG(type))
	up_write(&sbi->node_write);

Could you merge the diff into this patch?

>  
>  	if (put_pin_sem)
>  		up_read(&sbi->pin_sem);
> +
> +	if (IS_DATASEG(type))
> +		up_write(&sbi->node_write);
>  }
>  
>  static void update_device_state(struct f2fs_io_info *fio)
>