Re: [f2fs-dev] [PATCH] f2fs: fix to update user block counts in block_operations()

[Jaegeuk Kim <jaegeuk@kernel.org>]

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@oppo.com>
> Signed-off-by: Chao Yu <chao@kernel.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()?

> +
>  	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
> 


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