writeback: Protect inode->i_io_list with inode->i_lock

Currently, operations on inode->i_io_list are protected by
wb->list_lock. In the following patches we'll need to maintain
consistency between inode->i_state and inode->i_io_list so change the
code so that inode->i_lock protects also all inode's i_io_list handling.

Reviewed-by: Martijn Coenen <maco@android.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
CC: stable@vger.kernel.org # Prerequisite for "writeback: Avoid skipping inode writeback"
Signed-off-by: Jan Kara <jack@suse.cz>

fs/fs-writeback.c

@@ -144,6 +144,7 @@ static void inode_io_list_del_locked(struct inode *inode,
 				     struct bdi_writeback *wb)
 {
 	assert_spin_locked(&wb->list_lock);
+	assert_spin_locked(&inode->i_lock);
 
 	list_del_init(&inode->i_io_list);
 	wb_io_lists_depopulated(wb);
@@ -1122,7 +1123,9 @@ void inode_io_list_del(struct inode *inode)
 	struct bdi_writeback *wb;
 
 	wb = inode_to_wb_and_lock_list(inode);
+	spin_lock(&inode->i_lock);
 	inode_io_list_del_locked(inode, wb);
+	spin_unlock(&inode->i_lock);
 	spin_unlock(&wb->list_lock);
 }
 EXPORT_SYMBOL(inode_io_list_del);
@@ -1172,8 +1175,10 @@ void sb_clear_inode_writeback(struct inode *inode)
  * the case then the inode must have been redirtied while it was being written
  * out and we don't reset its dirtied_when.
  */
-static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
+static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
 {
+	assert_spin_locked(&inode->i_lock);
+
 	if (!list_empty(&wb->b_dirty)) {
 		struct inode *tail;
 
@@ -1184,6 +1189,13 @@ static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
 	inode_io_list_move_locked(inode, wb, &wb->b_dirty);
 }
 
+static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
+{
+	spin_lock(&inode->i_lock);
+	redirty_tail_locked(inode, wb);
+	spin_unlock(&inode->i_lock);
+}
+
 /*
  * requeue inode for re-scanning after bdi->b_io list is exhausted.
  */
@@ -1394,7 +1406,7 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
 		 * writeback is not making progress due to locked
 		 * buffers. Skip this inode for now.
 		 */
-		redirty_tail(inode, wb);
+		redirty_tail_locked(inode, wb);
 		return;
 	}
 
@@ -1414,15 +1426,15 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
 			 * retrying writeback of the dirty page/inode
 			 * that cannot be performed immediately.
 			 */
-			redirty_tail(inode, wb);
+			redirty_tail_locked(inode, wb);
 		}
 	} else if (inode->i_state & I_DIRTY) {
 		/*
 		 * Filesystems can dirty the inode during writeback operations,
 		 * such as delayed allocation during submission or metadata
 		 * updates after data IO completion.
 		 */
-		redirty_tail(inode, wb);
+		redirty_tail_locked(inode, wb);
 	} else if (inode->i_state & I_DIRTY_TIME) {
 		inode->dirtied_when = jiffies;
 		inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
@@ -1669,8 +1681,8 @@ static long writeback_sb_inodes(struct super_block *sb,
 		 */
 		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
+			redirty_tail_locked(inode, wb);
 			spin_unlock(&inode->i_lock);
-			redirty_tail(inode, wb);
 			continue;
 		}
 		if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {