[f2fs-dev] [PATCH v2] f2fs: fix to update user block counts in block_operations()

[f2fs-dev] [PATCH v2] f2fs: fix to update user block counts in block_operations()

[Chao Yu]

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>
---
v2:
- update user_block_counts in __prepare_cp_block() suggested by Jaegeuk.
 fs/f2fs/checkpoint.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 7cfe4e01dd7e..bdd96329dddd 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1186,6 +1186,11 @@ static void __prepare_cp_block(struct f2fs_sb_info *sbi)
 	ckpt->valid_node_count = cpu_to_le32(valid_node_count(sbi));
 	ckpt->valid_inode_count = cpu_to_le32(valid_inode_count(sbi));
 	ckpt->next_free_nid = cpu_to_le32(last_nid);
+
+	/* 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);
 }
 
 static bool __need_flush_quota(struct f2fs_sb_info *sbi)
@@ -1575,11 +1580,6 @@ 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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Re: [f2fs-dev] [PATCH v2] f2fs: fix to update user block counts in block_operations()

[patchwork-bot+f2fs]

Hello:

This patch was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:

On Tue, 25 Jun 2024 10:32:39 +0800 you 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
> 
> [...]

Here is the summary with links:
  - [f2fs-dev,v2] f2fs: fix to update user block counts in block_operations()
    https://git.kernel.org/jaegeuk/f2fs/c/f06c0f82e38b

You are awesome, thank you!
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