Re: [f2fs-dev] [PATCH 2/2] f2fs: fix data loss caused by incorrect use of nat_entry flag

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 3/10/26 17:36, Yongpeng Yang wrote:
> From: Yongpeng Yang <yangyongpeng@xiaomi.com>
> 
> Data loss can occur when fsync is performed on a newly created file
> (before any checkpoint has been written) concurrently with a checkpoint
> operation. The scenario is as follows:
> 
> create & write & fsync 'file A'                 write checkpoint
> - f2fs_do_sync_file // inline inode
>  - f2fs_write_inode // inode folio is dirty
>                                                 - f2fs_write_checkpoint
>                                                  - f2fs_flush_merged_writes
>                                                  - f2fs_sync_node_pages
>                                                  - f2fs_flush_nat_entries
>  - f2fs_fsync_node_pages // no dirty node
>  - f2fs_need_inode_block_update // return false
>  SPO and lost 'file A'
> 
> f2fs_flush_nat_entries() sets the IS_CHECKPOINTED and HAS_LAST_FSYNC
> flags for the nat_entry, but this does not mean that the checkpoint has
> actually completed successfully. However, f2fs_need_inode_block_update()
> checks these flags and incorrectly assumes that the checkpoint has
> finished.
> 
> The root cause is that the semantics of IS_CHECKPOINTED and
> HAS_LAST_FSYNC are only guaranteed after the checkpoint write fully
> completes.
> 
> This patch modifies f2fs_need_inode_block_update() to acquire the
> sbi->node_write lock before reading the nat_entry flags, ensuring that
> once IS_CHECKPOINTED and HAS_LAST_FSYNC are observed to be set, the
> checkpoint operation has already completed.
> 
> Fixes: e05df3b115e7 ("f2fs: add node operations")
> Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,


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