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

Chao Yu
2024-06-25T01:14:36Z

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@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()?

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
>>