btrfs: fix crash when tracepoint arguments are freed by wq callbacks

Enabling btrfs tracepoints leads to instant crash, as reported. The wq
callbacks could free the memory and the tracepoints started to
dereference the members to get to fs_info.

The proposed fix https://marc.info/?l=linux-btrfs&m=148172436722606&w=2
removed the tracepoints but we could preserve them by passing only the
required data in a safe way.

Fixes: bc074524e123 ("btrfs: prefix fsid to all trace events")
CC: stable@vger.kernel.org # 4.8+
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 13 insertions, 9 deletions

diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
index c14bed4ab097..b09225c77676 100644
--- a/include/trace/events/btrfs.h
+++ b/include/trace/events/btrfs.h
@@ -1157,22 +1157,26 @@ 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,
@@ -1191,9 +1195,9 @@ DEFINE_EVENT(btrfs__work, btrfs_work_sched,
 
 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,