tracing/fprobe: Unregister fprobe even if memory allocation fails

unregister_fprobe() can fail under memory pressure because of memory
allocation failure, but this maybe called from module unloading, and
usually there is no way to retry it. Moreover. trace_fprobe does not
check the return value.

To fix this problem, unregister fprobe and fprobe_hash_node even if
working memory allocation fails.
Anyway, if the last fprobe is removed, the filter will be freed.

Link: https://lore.kernel.org/all/177669365629.132053.8433032896213721288.stgit@mhiramat.tok.corp.google.com/

Fixes: 4346ba1 ("fprobe: Rewrite fprobe on function-graph tracer")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Author: mhiramat

kernel/trace/fprobe.c

@@ -324,9 +324,10 @@ static void fprobe_ftrace_remove_ips(unsigned long *addrs, int num)
 	lockdep_assert_held(&fprobe_mutex);
 
 	fprobe_ftrace_active--;
-	if (!fprobe_ftrace_active)
+	if (!fprobe_ftrace_active) {
 		unregister_ftrace_function(&fprobe_ftrace_ops);
-	if (num)
+		ftrace_free_filter(&fprobe_ftrace_ops);
+	} else if (num)
 		ftrace_set_filter_ips(&fprobe_ftrace_ops, addrs, num, 1, 0);
 }
 
@@ -525,10 +526,10 @@ static void fprobe_graph_remove_ips(unsigned long *addrs, int num)
 
 	fprobe_graph_active--;
 	/* Q: should we unregister it ? */
-	if (!fprobe_graph_active)
+	if (!fprobe_graph_active) {
 		unregister_ftrace_graph(&fprobe_graph_ops);
-
-	if (num)
+		ftrace_free_filter(&fprobe_graph_ops.ops);
+	} else if (num)
 		ftrace_set_filter_ips(&fprobe_graph_ops.ops, addrs, num, 1, 0);
 }
 
@@ -932,15 +933,19 @@ int unregister_fprobe(struct fprobe *fp)
 
 	hlist_array = fp->hlist_array;
 	addrs = kcalloc(hlist_array->size, sizeof(unsigned long), GFP_KERNEL);
-	if (!addrs) {
-		ret = -ENOMEM;	/* TODO: Fallback to one-by-one loop */
-		goto out;
-	}
+	/*
+	 * This will remove fprobe_hash_node from the hash table even if
+	 * memory allocation fails. However, ftrace_ops will not be updated.
+	 * Anyway, when the last fprobe is unregistered, ftrace_ops is also
+	 * unregistered.
+	 */
+	if (!addrs)
+		pr_warn("Failed to allocate working array. ftrace_ops may not sync.\n");
 
 	/* Remove non-synonim ips from table and hash */
 	count = 0;
 	for (i = 0; i < hlist_array->size; i++) {
-		if (!delete_fprobe_node(&hlist_array->array[i]))
+		if (!delete_fprobe_node(&hlist_array->array[i]) && addrs)
 			addrs[count++] = hlist_array->array[i].addr;
 	}
 	del_fprobe_hash(fp);