[PATCH] netfs: Fix the netfs_folio tracepoint to handle NULL mapping

[David Howells]

Fix the netfs_folio tracepoint to handle folios that have a NULL mapping
pointer.  In such a case, just substitute a zero inode number.

Fixes: c38f4e96e605 ("netfs: Provide func to copy data to pagecache for buffered write")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: netfs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
 include/trace/events/netfs.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 76bd42a96815..1d7c52821e55 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -448,7 +448,8 @@ TRACE_EVENT(netfs_folio,
 			     ),
 
 	    TP_fast_assign(
-		    __entry->ino = folio->mapping->host->i_ino;
+		    struct address_space *__m = READ_ONCE(folio->mapping);
+		    __entry->ino = __m ? __m->host->i_ino : 0;
 		    __entry->why = why;
 		    __entry->index = folio_index(folio);
 		    __entry->nr = folio_nr_pages(folio);