[PATCH v2] writeback: Add asserts for adding freed inode to lists

[Jan Kara <jack@suse.cz>]

In the past we had several use-after-free issues with inodes getting
added to writeback lists after evict() removed them. These are painful
to debug so add some asserts to catch the problem earlier. The only
non-obvious change in the commit is that we need to tweak
redirty_tail_locked() to avoid triggering assertion in
inode_io_list_move_locked().

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/fs-writeback.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

New version of the patch with improved changelog and added comment to
redirty_tail_locked().

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 443f83382b9b..6cd172c4cb3e 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -121,6 +121,7 @@ static bool inode_io_list_move_locked(struct inode *inode,
 {
 	assert_spin_locked(&wb->list_lock);
 	assert_spin_locked(&inode->i_lock);
+	WARN_ON_ONCE(inode->i_state & I_FREEING);
 
 	list_move(&inode->i_io_list, head);
 
@@ -280,6 +281,7 @@ static void inode_cgwb_move_to_attached(struct inode *inode,
 {
 	assert_spin_locked(&wb->list_lock);
 	assert_spin_locked(&inode->i_lock);
+	WARN_ON_ONCE(inode->i_state & I_FREEING);
 
 	inode->i_state &= ~I_SYNC_QUEUED;
 	if (wb != &wb->bdi->wb)
@@ -1129,6 +1131,7 @@ static void inode_cgwb_move_to_attached(struct inode *inode,
 {
 	assert_spin_locked(&wb->list_lock);
 	assert_spin_locked(&inode->i_lock);
+	WARN_ON_ONCE(inode->i_state & I_FREEING);
 
 	inode->i_state &= ~I_SYNC_QUEUED;
 	list_del_init(&inode->i_io_list);
@@ -1294,6 +1297,17 @@ static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
 {
 	assert_spin_locked(&inode->i_lock);
 
+	inode->i_state &= ~I_SYNC_QUEUED;
+	/*
+	 * When the inode is being freed just don't bother with dirty list
+	 * tracking. Flush worker will ignore this inode anyway and it will
+	 * trigger assertions in inode_io_list_move_locked().
+	 */
+	if (inode->i_state & I_FREEING) {
+		list_del_init(&inode->i_io_list);
+		wb_io_lists_depopulated(wb);
+		return;
+	}
 	if (!list_empty(&wb->b_dirty)) {
 		struct inode *tail;
 
@@ -1302,7 +1316,6 @@ static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
 			inode->dirtied_when = jiffies;
 	}
 	inode_io_list_move_locked(inode, wb, &wb->b_dirty);
-	inode->i_state &= ~I_SYNC_QUEUED;
 }
 
 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
-- 
2.35.3