netfs: Fix the netfs_folio tracepoint to handle NULL mapping

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: c38f4e9 ("netfs: Provide func to copy data to pagecache for buffered write")
Signed-off-by: David Howells <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
cc: Jeff Layton <[email protected]>
cc: [email protected]
cc: [email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: dhowells

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);