f2fs: introduce help macro on_build_free_nids()

Introduce help macro on_build_free_nids() which just uses build_lock
to judge whether the building free nid is going, so that we can remove
the on_build_free_nids field from f2fs_sb_info.
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
[Jaegeuk Kim: remove an unnecessary white line removal]
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/f2fs.h

@@ -417,7 +417,6 @@ struct f2fs_sb_info {
 	struct mutex node_write;		/* locking node writes */
 	struct mutex writepages;		/* mutex for writepages() */
 	bool por_doing;				/* recovery is doing or not */
-	bool on_build_free_nids;		/* build_free_nids is doing */
 	wait_queue_head_t cp_wait;
 
 	/* for orphan inode management */

fs/f2fs/node.c

@@ -21,6 +21,8 @@
 #include "segment.h"
 #include <trace/events/f2fs.h>
 
+#define on_build_free_nids(nmi) mutex_is_locked(&nm_i->build_lock)
+
 static struct kmem_cache *nat_entry_slab;
 static struct kmem_cache *free_nid_slab;
 
@@ -1422,7 +1424,7 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
 	spin_lock(&nm_i->free_nid_list_lock);
 
 	/* We should not use stale free nids created by build_free_nids */
-	if (nm_i->fcnt && !sbi->on_build_free_nids) {
+	if (nm_i->fcnt && !on_build_free_nids(nm_i)) {
 		f2fs_bug_on(list_empty(&nm_i->free_nid_list));
 		list_for_each(this, &nm_i->free_nid_list) {
 			i = list_entry(this, struct free_nid, list);
@@ -1441,9 +1443,7 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
 
 	/* Let's scan nat pages and its caches to get free nids */
 	mutex_lock(&nm_i->build_lock);
-	sbi->on_build_free_nids = true;
 	build_free_nids(sbi);
-	sbi->on_build_free_nids = false;
 	mutex_unlock(&nm_i->build_lock);
 	goto retry;
 }