cachefiles: Trace active-mark failure

Add a tracepoint to log failure to apply an active mark to a file in
addition to tracing successfully setting and unsetting the mark.

Also include the backing file inode number in the message logged to dmesg.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/164251404666.3435901.17331742792401482190.stgit@warthog.procyon.org.uk/ # v1

fs/cachefiles/namei.c

@@ -25,7 +25,9 @@ static bool __cachefiles_mark_inode_in_use(struct cachefiles_object *object,
 		trace_cachefiles_mark_active(object, inode);
 		can_use = true;
 	} else {
-		pr_notice("cachefiles: Inode already in use: %pd\n", dentry);
+		trace_cachefiles_mark_failed(object, inode);
+		pr_notice("cachefiles: Inode already in use: %pd (B=%lx)\n",
+			  dentry, inode->i_ino);
 	}
 
 	return can_use;

include/trace/events/cachefiles.h

@@ -573,6 +573,27 @@ TRACE_EVENT(cachefiles_mark_active,
 		      __entry->obj, __entry->inode)
 	    );
 
+TRACE_EVENT(cachefiles_mark_failed,
+	    TP_PROTO(struct cachefiles_object *obj,
+		     struct inode *inode),
+
+	    TP_ARGS(obj, inode),
+
+	    /* Note that obj may be NULL */
+	    TP_STRUCT__entry(
+		    __field(unsigned int,		obj		)
+		    __field(ino_t,			inode		)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->obj	= obj ? obj->debug_id : 0;
+		    __entry->inode	= inode->i_ino;
+			   ),
+
+	    TP_printk("o=%08x B=%lx",
+		      __entry->obj, __entry->inode)
+	    );
+
 TRACE_EVENT(cachefiles_mark_inactive,
 	    TP_PROTO(struct cachefiles_object *obj,
 		     struct inode *inode),