linux-kernel - Re: [PATCH] f2fs: fix to update user block counts in block

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Message-ID: <f0adf39a-5c07-49bd-910d-eebbc5f41dc1@kernel.org>
Date: Tue, 25 Jun 2024 09:14:33 +0800
From: Chao Yu <chao@...nel.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
 Yunlei He <heyunlei@...o.com>
Subject: Re: [PATCH] f2fs: fix to update user block counts in
 block_operations()

On 2024/6/25 1:53, Jaegeuk Kim wrote:
> On 06/06, Chao Yu wrote:
>> Commit 59c9081bc86e ("f2fs: allow write page cache when writting cp")
>> allows write() to write data to page cache during checkpoint, so block
>> count fields like .total_valid_block_count, .alloc_valid_block_count
>> and .rf_node_block_count may encounter race condition as below:
>>
>> CP				Thread A
>> - write_checkpoint
>>   - block_operations
>>    - f2fs_down_write(&sbi->node_change)
>>    - __prepare_cp_block
>>    : ckpt->valid_block_count = .total_valid_block_count
>>    - f2fs_up_write(&sbi->node_change)
>> 				- write
>> 				 - f2fs_preallocate_blocks
>> 				  - f2fs_map_blocks(,F2FS_GET_BLOCK_PRE_AIO)
>> 				   - f2fs_map_lock
>> 				    - f2fs_down_read(&sbi->node_change)
>> 				   - f2fs_reserve_new_blocks
>> 				    - inc_valid_block_count
>> 				    : percpu_counter_add(&sbi->alloc_valid_block_count, count)
>> 				    : sbi->total_valid_block_count += count
>> 				    - f2fs_up_read(&sbi->node_change)
>>   - do_checkpoint
>>   : sbi->last_valid_block_count = sbi->total_valid_block_count
>>   : percpu_counter_set(&sbi->alloc_valid_block_count, 0)
>>   : percpu_counter_set(&sbi->rf_node_block_count, 0)
>> 				- fsync
>> 				 - need_do_checkpoint
>> 				  - f2fs_space_for_roll_forward
>> 				  : alloc_valid_block_count was reset to zero,
>> 				    so, it may missed last data during checkpoint
>>
>> Let's change to update .total_valid_block_count, .alloc_valid_block_count
>> and .rf_node_block_count in block_operations(), then their access can be
>> protected by .node_change and .cp_rwsem lock, so that it can avoid above
>> race condition.
>>
>> Fixes: 59c9081bc86e ("f2fs: allow write page cache when writting cp")
>> Cc: Yunlei He <heyunlei@...o.com>
>> Signed-off-by: Chao Yu <chao@...nel.org>
>> ---
>>   fs/f2fs/checkpoint.c | 11 ++++++-----
>>   1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>> index 66eaad591b60..010bbd5af211 100644
>> --- a/fs/f2fs/checkpoint.c
>> +++ b/fs/f2fs/checkpoint.c
>> @@ -1298,6 +1298,12 @@ static int block_operations(struct f2fs_sb_info *sbi)
>>   	 * dirty node blocks and some checkpoint values by block allocation.
>>   	 */
>>   	__prepare_cp_block(sbi);
>> +
>> +	/* update user_block_counts */
>> +	sbi->last_valid_block_count = sbi->total_valid_block_count;
>> +	percpu_counter_set(&sbi->alloc_valid_block_count, 0);
>> +	percpu_counter_set(&sbi->rf_node_block_count, 0);
> 
> Need to add this in __prepare_cp_block()?

Fine to me, will update in v2.

Thanks,

> 
>> +
>>   	f2fs_up_write(&sbi->node_change);
>>   	return err;
>>   }
>> @@ -1575,11 +1581,6 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>   		start_blk += NR_CURSEG_NODE_TYPE;
>>   	}
>>   
>> -	/* update user_block_counts */
>> -	sbi->last_valid_block_count = sbi->total_valid_block_count;
>> -	percpu_counter_set(&sbi->alloc_valid_block_count, 0);
>> -	percpu_counter_set(&sbi->rf_node_block_count, 0);
>> -
>>   	/* Here, we have one bio having CP pack except cp pack 2 page */
>>   	f2fs_sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO);
>>   	/* Wait for all dirty meta pages to be submitted for IO */
>> -- 
>> 2.40.1
>>