ext4: test if inode's all dirty pages are submitted to disk

The commit aa373cf550 ("writeback: stop background/kupdate works from
livelocking other works") introduced an issue where unmounting a filesystem
in a multi-logical-partition scenario could lead to batch file data loss.
This problem was not fixed until the commit d92109891f ("fs/writeback:
bail out if there is no more inodes for IO and queued once"). It took
considerable time to identify the root cause. Additionally, in actual
production environments, we frequently encountered file data loss after
normal system reboots. Therefore, we are adding a check in the inode
release flow to verify whether all dirty pages have been flushed to disk,
in order to determine whether the data loss is caused by a logic issue in
the filesystem code.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260303012242.3206465-1-yebin@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/inode.c

@@ -186,6 +186,14 @@ void ext4_evict_inode(struct inode *inode)
 	if (EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL)
 		ext4_evict_ea_inode(inode);
 	if (inode->i_nlink) {
+		/*
+		 * If there's dirty page will lead to data loss, user
+		 * could see stale data.
+		 */
+		if (unlikely(!ext4_emergency_state(inode->i_sb) &&
+		    mapping_tagged(&inode->i_data, PAGECACHE_TAG_DIRTY)))
+			ext4_warning_inode(inode, "data will be lost");
+
 		truncate_inode_pages_final(&inode->i_data);
 
 		goto no_delete;