f2fs: fix data loss caused by incorrect use of nat_entry flag

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>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index a9cd2803e681b5ae34ab80349baa929eab6073eb..662a61306ec67b5f2079607f03be310211f7129b 100644 (file)
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -427,7 +427,9 @@ bool f2fs_need_inode_block_update(struct f2fs_sb_info *sbi, nid_t ino)
        struct f2fs_nm_info *nm_i = NM_I(sbi);
        struct nat_entry *e;
        bool need_update = true;
+       struct f2fs_lock_context lc;
 
+       f2fs_down_read_trace(&sbi->node_write, &lc);
        f2fs_down_read(&nm_i->nat_tree_lock);
        e = __lookup_nat_cache(nm_i, ino, false);
        if (e && get_nat_flag(e, HAS_LAST_FSYNC) &&
@@ -435,6 +437,7 @@ bool f2fs_need_inode_block_update(struct f2fs_sb_info *sbi, nid_t ino)
                         get_nat_flag(e, HAS_FSYNCED_INODE)))
                need_update = false;
        f2fs_up_read(&nm_i->nat_tree_lock);
+       f2fs_up_read_trace(&sbi->node_write, &lc);
        return need_update;
 }