Lock-annotate some kernel functions as an example of how it works.

In particular, a function that is called with a lock held, and
releases it only to re-acquire it needs to be annotated as such,
since otherwise sparse will complain about an unexpected unlock,
even though "globally" the lock is constant over the call.

fs/file.c

@@ -54,6 +54,8 @@ void free_fd_array(struct file **array, int num)
  */
 
 int expand_fd_array(struct files_struct *files, int nr)
+	__releases(files->file_lock)
+	__acquires(files->file_lock)
 {
 	struct file **new_fds;
 	int error, nfds;
@@ -157,6 +159,8 @@ void free_fdset(fd_set *array, int num)
  * held for write.
  */
 int expand_fdset(struct files_struct *files, int nr)
+	__releases(file->file_lock)
+	__acquires(file->file_lock)
 {
 	fd_set *new_openset = NULL, *new_execset = NULL;
 	int error, nfds = 0;

init/main.c

@@ -441,6 +441,7 @@ static void __init smp_init(void)
  */
 
 static void noinline rest_init(void)
+	__releases(kernel_lock)
 {
 	kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);
 	numa_default_policy();

kernel/resource.c

@@ -57,6 +57,7 @@ static void *r_next(struct seq_file *m, void *v, loff_t *pos)
 }
 
 static void *r_start(struct seq_file *m, loff_t *pos)
+	__acquires(resource_lock)
 {
 	struct resource *p = m->private;
 	loff_t l = 0;
@@ -67,6 +68,7 @@ static void *r_start(struct seq_file *m, loff_t *pos)
 }
 
 static void r_stop(struct seq_file *m, void *v)
+	__releases(resource_lock)
 {
 	read_unlock(&resource_lock);
 }