Patch "btrfs: fix crash when tracepoint arguments are freed by wq callbacks" has been added to the 4.9-stable tree

@@ -273,6 +273,8 @@ static void run_ordered_work(struct __bt
 	unsigned long flags;
 
 	while (1) {
+		void *wtag;
+
 		spin_lock_irqsave(lock, flags);
 		if (list_empty(list))
 			break;

@@ -299,11 +301,13 @@ static void run_ordered_work(struct __bt
 		spin_unlock_irqrestore(lock, flags);
 
 		/*
-		 * we don't want to call the ordered free functions
-		 * with the lock held though
+		 * We don't want to call the ordered free functions with the
+		 * lock held though. Save the work as tag for the trace event,
+		 * because the callback could free the structure.
 		 */
+		wtag = work;
 		work->ordered_free(work);
-		trace_btrfs_all_work_done(work);
+		trace_btrfs_all_work_done(wq->fs_info, wtag);
 	}
 	spin_unlock_irqrestore(lock, flags);
 }

@@ -311,6 +315,7 @@ static void run_ordered_work(struct __bt
 static void normal_work_helper(struct btrfs_work *work)
 {
 	struct __btrfs_workqueue *wq;
+	void *wtag;
 	int need_order = 0;
 
 	/*

@@ -324,6 +329,8 @@ static void normal_work_helper(struct bt
 	if (work->ordered_func)
 		need_order = 1;
 	wq = work->wq;
+	/* Safe for tracepoints in case work gets freed by the callback */
+	wtag = work;
 
 	trace_btrfs_work_sched(work);
 	thresh_exec_hook(wq);

@@ -333,7 +340,7 @@ static void normal_work_helper(struct bt
 		run_ordered_work(wq);
 	}
 	if (!need_order)
-		trace_btrfs_all_work_done(work);
+		trace_btrfs_all_work_done(wq->fs_info, wtag);
 }
 
 void btrfs_init_work(struct btrfs_work *work, btrfs_work_func_t uniq_func,

@@ -1162,22 +1162,26 @@ DECLARE_EVENT_CLASS(btrfs__work,
 		   __entry->func, __entry->ordered_func, __entry->ordered_free)
 );
 
-/* For situiations that the work is freed */
+/*
+ * For situiations when the work is freed, we pass fs_info and a tag that that
+ * matches address of the work structure so it can be paired with the
+ * scheduling event.
+ */
 DECLARE_EVENT_CLASS(btrfs__work__done,
 
-	TP_PROTO(struct btrfs_work *work),
+	TP_PROTO(struct btrfs_fs_info *fs_info, void *wtag),
 
-	TP_ARGS(work),
+	TP_ARGS(fs_info, wtag),
 
 	TP_STRUCT__entry_btrfs(
-		__field(	void *,	work			)
+		__field(	void *,	wtag			)
 	),
 
-	TP_fast_assign_btrfs(btrfs_work_owner(work),
-		__entry->work		= work;
+	TP_fast_assign_btrfs(fs_info,
+		__entry->wtag		= wtag;
 	),
 
-	TP_printk_btrfs("work->%p", __entry->work)
+	TP_printk_btrfs("work->%p", __entry->wtag)
 );
 
 DEFINE_EVENT(btrfs__work, btrfs_work_queued,

@@ -1196,9 +1200,9 @@ DEFINE_EVENT(btrfs__work, btrfs_work_sch
 
 DEFINE_EVENT(btrfs__work__done, btrfs_all_work_done,
 
-	TP_PROTO(struct btrfs_work *work),
+	TP_PROTO(struct btrfs_fs_info *fs_info, void *wtag),
 
-	TP_ARGS(work)
+	TP_ARGS(fs_info, wtag)
 );
 
 DEFINE_EVENT(btrfs__work, btrfs_ordered_sched,