[PATCH] f2fs: fix livelock in f2fs_sync_inode_meta()

[Daeho Jeong]

From: Daeho Jeong <daehojeong@xxxxxxxxxx>

During checkpoint, f2fs_sync_inode_meta() iterates over dirty inodes in
the DIRTY_META list. If igrab() fails on an inode (e.g. because it is in
the freeing state), the loop continues without moving the current inode to
the tail of the list. As a result, subsequent iterations pick the same
inode repeatedly, preventing other ready dirty inodes in the list from
making forward progress and leading to a livelock.

Fix this by moving the current inode to the tail of the list
(list_move_tail(&fi->gdirty_list, head)) before attempting igrab().

Additionally, if igrab() fails, the freeing inode may be waiting for its
pending writeback data pages to complete during eviction.
Submit any pending merged data writes and yield the
CPU with cond_resched() to allow the eviction to make progress.

Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
---
 fs/f2fs/checkpoint.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index ef22692cef0a..5597033533b0 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1460,6 +1460,7 @@ static int f2fs_sync_inode_meta(struct f2fs_sb_info *sbi)
 		}
 		fi = list_first_entry(head, struct f2fs_inode_info,
 							gdirty_list);
+		list_move_tail(&fi->gdirty_list, head);
 		inode = igrab(&fi->vfs_inode);
 		spin_unlock(&sbi->inode_lock[DIRTY_META]);
 		if (inode) {
@@ -1469,6 +1470,13 @@ static int f2fs_sync_inode_meta(struct f2fs_sb_info *sbi)
 			if (is_inode_flag_set(inode, FI_DIRTY_INODE))
 				f2fs_update_inode_page(inode);
 			iput(inode);
+		} else {
+			/*
+			 * We should submit bio, since it exists several
+			 * writebacking pages in the freeing inode.
+			 */
+			f2fs_submit_merged_write(sbi, DATA);
+			cond_resched();
 		}
 	}
 	return 0;
-- 
2.55.0.979.g7e5102b832-goog