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

Jaegeuk Kim
2024-06-24T17:53:27Z

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
>